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Unable to bind viewmodel property - my own user control (WPF) [duplicate]

This question already has answers here:
Issue with DependencyProperty binding
(3 answers)
Closed 2 years ago.
The problem is quite known and popular ...
I went through many threads today, but none of them allowed me to solve my problem, so I decided to ask you for help. I think I follow all the tips of other users...
CustomControl.xaml:
<UserControl x:Class="X.UserControls.CustomUserControl"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
mc:Ignorable="d"
x:Name="eqAction"
DataContext="{Binding RelativeSource={RelativeSource Self}}">
<StackPanel Orientation="Horizontal" VerticalAlignment="Center">
<TextBlock Text="{Binding Path=FirstName, RelativeSource={RelativeSource Mode=FindAncestor, AncestorType={x:Type UserControl}}, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" />
</StackPanel>
</UserControl>
CustomControl.xaml.cs:
public partial class CustomControl : UserControl
{
public static readonly DependencyProperty FirstNameProperty = DependencyProperty.Register(
"FirstName",
typeof(string),
typeof(CustomControl),
new FrameworkPropertyMetadata(default(string),
FrameworkPropertyMetadataOptions.BindsTwoWayByDefault));
public string FirstName
{
get
{
return (string)GetValue(FirstNameProperty);
}
set
{
SetValue(FirstNameProperty, value);
}
}
public CustomControl()
{
InitializeComponent();
}
}
MainViewModel.cs:
private string _test;
public string Test
{
get { return _test; }
set
{
_test = value;
OnPropertyChanged(string.Empty);
}
}
public MainViewModel()
{
Test = "abc";
}
public new event PropertyChangedEventHandler PropertyChanged;
protected void OnPropertyChanged(string propertyName)
{
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
}
MainUserControl.xaml
<StackPanel x:Name="NotWorking">
<userControls:CustomControl FirstName="{Binding Path=Test, Mode=TwoWay}" />
</StackPanel>
<StackPanel x:Name="Working">
<userControls:CustomControl FirstName="My string value that works" />
</StackPanel>
<StackPanel x:Name="WorkingToo">
<TextBlock Text="{Binding Path=Test, Mode=TwoWay}" />
</StackPanel>
In my MainUserControl.xaml file I have three stackpanels. The first is what I want to achieve. Unfortunately, no data is currently binded (nothing displayed).
However, when instead of binding I assign a string value to the property, the text will be displayed correctly (example 2).
Example 3: when I create a binding to e.g. a textblock component, the text will also be displayed ... Only one control that appears in the first stackpanel (name NotWorking) works differently ...
Do you see the mistake?

the problem is the line where you set the datacontext in the MainUserControl:
DataContext="{Binding RelativeSource={RelativeSource Self}}"
When you set the DataContext as in your code, the binding in the MainUserControl will look for a property named Test in the CustomControl and not in the MainViewModel.

How do I Access Buttons inside a UserControl from xaml?

At work I have several pages, each with buttons in the same places, and with the same properties. Each page also has minor differences. To that end, we created a userControl Template and put all the buttons in it, then applied that user control to all the pages. However, now it's rather hard to access the buttons and modify them from each page's xaml, because they are inside a UserControl on the page..... How do I elegantly access the buttons from each page?
What I've tried:
Currently, we bind to a bunch of dependency properties. I don't like this option because I have a lot of buttons, and need to control a lot of properties on those buttons. The result is hundreds of dependency properties, and a real mess to wade through when we need to change something.
Another method is to use styles. I like this method generally, but because these buttons are inside another control it becomes difficult to modify them, and the template would only be exactly right for one button, at one time.
Adam Kemp posted about letting the user just insert their own button here, and this is the method I'm currently trying to impliment / modify. Unfortunately, I don't have access to Xamarin.
Although the template is inserted when the code runs, the template is not updating the button correctly. If I put a breakpoint in the MyButton Setter, I can see that value is actually an empty button, rather than the one I assigned in my main window. How do I fix this?
Here's some simplified Code:
My Template UserControl's xaml:
<UserControl x:Class="TemplateCode.Template"
x:Name="TemplatePage"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
mc:Ignorable="d"
d:DesignHeight="350"
d:DesignWidth="525"
DataContext="{Binding RelativeSource={RelativeSource Self}}"
Background="DarkGray">
<Grid>
<Button x:Name="_button" Width="200" Height="100" Content="Template Button"/>
</Grid>
</UserControl>
My Template UserControl's Code Behind:
using System.Windows.Controls;
namespace TemplateCode
{
public partial class Template : UserControl
{
public static Button DefaultButton;
public Template()
{
InitializeComponent();
}
public Button MyButton
{
get
{
return _button;
}
set
{
_button = value; //I get here, but value is a blank button?!
// Eventually, I'd like to do something like:
// Foreach (property in value)
// {
// If( value.property != DefaultButton.property) )
// {
// _button.property = value.property;
// }
// }
// This way users only have to update some of the properties
}
}
}
}
And now the application where I want to use it:
<Window x:Class="TemplateCode.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
mc:Ignorable="d"
xmlns:templateCode="clr-namespace:TemplateCode"
Title="MainWindow"
Height="350"
Width="525"
Background="LimeGreen"
DataContext="{Binding RelativeSource={RelativeSource Self}}" >
<Grid>
<templateCode:Template>
<templateCode:Template.MyButton>
<Button Background="Yellow"
Content="Actual Button"
Width="200"
Height="100"/>
</templateCode:Template.MyButton>
</templateCode:Template>
</Grid>
</Window>
And Now the Code Behind:
Using System.Windows;
Namespace TemplateCode
{
Public partial class MainWindow : Window
{
Public MainWindow()
{
InitializeComponent();
}
}
}
Edit: While I want to remove unnecessary dependency properties in the template userControl, I'd still like to set bindings on the button's properties from the XAML.

rather than use many dependency properties, prefer style approach. Style contains every property available for a Button control.
I would create a DependencyProperty for each button style in UserControl.
public partial class TemplateUserControl : UserControl
{
public TemplateUserControl()
{
InitializeComponent();
}
public static readonly DependencyProperty FirstButtonStyleProperty =
DependencyProperty.Register("FirstButtonStyle", typeof (Style), typeof (TemplateUserControl));
public Style FirstButtonStyle
{
get { return (Style)GetValue(FirstButtonStyleProperty); }
set { SetValue(FirstButtonStyleProperty, value); }
}
public static readonly DependencyProperty SecondButtonStyleProperty =
DependencyProperty.Register("SecondButtonStyle", typeof (Style), typeof (TemplateUserControl));
public Style SecondButtonStyle
{
get { return (Style)GetValue(SecondButtonStyleProperty); }
set { SetValue(SecondButtonStyleProperty, value); }
}
}
and then modify xaml for buttons to pick these styles:
<UserControl x:Class="MyApp.TemplateUserControl"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
mc:Ignorable="d"
d:DesignHeight="200" d:DesignWidth="300"
Background="DarkGray">
<StackPanel>
<Button x:Name="_button" Width="200" Height="100"
Style="{Binding Path=FirstButtonStyle, RelativeSource={RelativeSource AncestorType=UserControl}}"/>
<Button x:Name="_button2" Width="200" Height="100"
Style="{Binding Path=SecondButtonStyle, RelativeSource={RelativeSource AncestorType=UserControl}}"/>
</StackPanel>
</UserControl>
now when buttons have to be customized, that can achieved by custom styles:
<StackPanel>
<StackPanel.Resources>
<!--common theme properties-->
<Style TargetType="Button" x:Key="TemplateButtonBase">
<Setter Property="FontSize" Value="18"/>
<Setter Property="Foreground" Value="Blue"/>
</Style>
<!--unique settings of the 1st button-->
<!--uses common base style-->
<Style TargetType="Button" x:Key="BFirst" BasedOn="{StaticResource TemplateButtonBase}">
<Setter Property="Content" Value="1st"/>
</Style>
<Style TargetType="Button" x:Key="BSecond" BasedOn="{StaticResource TemplateButtonBase}">
<Setter Property="Content" Value="2nd"/>
</Style>
</StackPanel.Resources>
<myApp:TemplateUserControl FirstButtonStyle="{StaticResource BFirst}"
SecondButtonStyle="{StaticResource BSecond}"/>
</StackPanel>

You could register a Dependency Property Button on your UserControland handle the initialization in its PropertyChangedCallback.
Template.xaml.cs
using System;
using System.Windows;
using System.Windows.Controls;
using System.Collections.Generic;
using System.Windows.Markup.Primitives;
namespace TemplateCode
{
public partial class Template : UserControl
{
public Template()
{
InitializeComponent();
}
public static readonly DependencyProperty ButtonProperty =
DependencyProperty.Register("Button", typeof(Button), typeof(Template),
new UIPropertyMetadata(new PropertyChangedCallback(ButtonChangedCallback)));
public Button Button
{
get { return (Button)GetValue(ButtonProperty); }
set { SetValue(ButtonProperty, value); }
}
public static List<DependencyProperty> GetDependencyProperties(Object element)
{
List<DependencyProperty> properties = new List<DependencyProperty>();
MarkupObject markupObject = MarkupWriter.GetMarkupObjectFor(element);
if (markupObject != null)
{
foreach (MarkupProperty mp in markupObject.Properties)
{
if (mp.DependencyProperty != null)
{
properties.Add(mp.DependencyProperty);
}
}
}
return properties;
}
private static void ButtonChangedCallback(object sender, DependencyPropertyChangedEventArgs args)
{
// Get button defined by user in MainWindow
Button userButton = (Button)args.NewValue;
// Get template button in UserControl
UserControl template = (UserControl)sender;
Button templateButton = (Button)template.FindName("button");
// Get userButton props and change templateButton accordingly
List<DependencyProperty> properties = GetDependencyProperties(userButton);
foreach(DependencyProperty property in properties)
{
if (templateButton.GetValue(property) != userButton.GetValue(property))
{
templateButton.SetValue(property, userButton.GetValue(property));
}
}
}
}
}
Template.xaml
UserControl DataContext is inherited from parent, no need not to set it explicitly
<UserControl x:Class="TemplateCode.Template"
x:Name="TemplatePage"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
mc:Ignorable="d"
d:DesignHeight="350"
d:DesignWidth="525"
Background="DarkGray">
<Grid>
<Button x:Name="button" Width="200" Height="100" Content="Template Button"/>
</Grid>
</UserControl>
MainWindow.xaml
You were setting Button.Content instead of Button
<Window x:Class="TemplateCode.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
mc:Ignorable="d"
xmlns:templateCode="clr-namespace:TemplateCode"
Title="MainWindow"
Height="350"
Width="525">
<Window.Resources>
<Button x:Key="UserButton"
Background="Yellow"
Content="Actual Button"
Width="200"
Height="100"
/>
</Window.Resources>
<Grid>
<templateCode:Template Button="{StaticResource UserButton}"/>
</Grid>
</Window>
EDIT - Binding Button.Content
3 ways to do this:
1. Dependency Properties
By far the best method. Creating UserControl DP's for every property on the Button is certainly overkill, but for those you want bound to the ViewModel / MainWindow DataContext it makes sense.
Adding in Template.xaml.cs
public static readonly DependencyProperty TextProperty =
DependencyProperty.Register("Text", typeof(string), typeof(Template));
public string Text
{
get { return (string)GetValue(TextProperty); }
set { SetValue(TextProperty, value); }
}
Template.xaml
<UserControl x:Class="TemplateCode.Template"
...
DataContext="{Binding RelativeSource={RelativeSource Self}}">
<Grid>
<Button x:Name="button" Width="200" Height="100" Content="{Binding Text}"/>
</Grid>
</UserControl>
MainWindow.xaml
<Window.Resources>
<Button x:Key="UserButton"
Background="Yellow"
Width="200"
Height="100"
/>
</Window.Resources>
<Grid>
<templateCode:Template
Button="{StaticResource UserButton}"
Text="{Binding DataContext.Txt,
RelativeSource={RelativeSource AncestorType={x:Type Window}}}"/>
</Grid>
Or
<Window.Resources>
<Button x:Key="UserButton"
Background="Yellow"
Content="Actual Button"
Width="200"
Height="100"
/>
</Window.Resources>
<Grid>
<templateCode:Template
Button="{StaticResource UserButton}"/>
</Grid>
Value precedence: UserButton Content > DP Text, so setting the Content in Resources wins.
2. Creating the Button in your ViewModel
MVVM purists won't like this, but you could use the Binding mark up instead of StaticResource.
MainWindow.xaml
<Grid>
<templateCode:Template
Button="{Binding DataContext.UserButton,
RelativeSource={RelativeSource AncestorType={x:Type Window}}}"/>
</Grid>
3. Setting the binding in code
As you already noticed, a ViewModel prop (e.g. Txt) can't be referenced in Resources because of the order everything is initialized. You can still do it in code later, but it gets a bit messy with the error to prove.
System.Windows.Data Error: 4 : Cannot find source for binding with
reference 'RelativeSource FindAncestor,
AncestorType='System.Windows.Window', AncestorLevel='1''.
BindingExpression:Path=DataContext.Txt; DataItem=null; target element
is 'Button' (Name=''); target property is 'Content' (type 'Object')
Note you need to define the full path on the Content property (setting DataContext on parent won't do).
MainWindow.xaml
<Window.Resources>
<Button x:Key="UserButton"
Background="Yellow"
Width="200"
Height="100"
Content="{Binding DataContext.Txt,
RelativeSource={RelativeSource AncestorType={x:Type Window}}}"
/>
</Window.Resources>
<Grid>
<templateCode:Template Button="{StaticResource UserButton}"/>
</Grid>
Template.xaml.cs
private static void ButtonChangedCallback(object sender, DependencyPropertyChangedEventArgs args)
{
// Get button defined by user in MainWindow
Button userButton = (Button)args.NewValue;
// Get template button in UserControl
UserControl template = (UserControl)sender;
Button templateButton = (Button)template.FindName("button");
// Get userButton props and change templateButton accordingly
List<DependencyProperty> properties = GetDependencyProperties(userButton);
foreach (DependencyProperty property in properties)
{
if (templateButton.GetValue(property) != userButton.GetValue(property))
templateButton.SetValue(property, userButton.GetValue(property));
}
// Set Content binding
BindingExpression bindingExpression = userButton.GetBindingExpression(Button.ContentProperty);
if (bindingExpression != null)
templateButton.SetBinding(Button.ContentProperty, bindingExpression.ParentBinding);
}

If you can group your changes to your buttons to one or multiple properties on your datacontext, you could work with DataTriggers:
<Button x:Name="TestButton">
<Button.Style>
<Style>
<Style.Triggers>
<DataTrigger Binding="{Binding IsButtonEnabled}" Value="True">
<Setter TargetName="TestButton" Property="Background" Value="Red" />
</DataTrigger>
</Style.Triggers>
</Style>
</Button.Style>
</Button>
You can even use multiple conditions with MultiDataTriggers.

The main problem is that Template components are initialized before mainwindow components.I mean all properties of the button in mainwindow are set after the button in template class is initialized. Therefore, as you said value sets to null. All I want to say is about sequence of initializing objects.If you make a trick such a way as follows ;
public partial class Template : UserControl
{
private Button _btn ;
public Template()
{
}
public Button MyButton
{
get
{
return _button;
}
set
{
_btn = value;
_button = value;
}
}
protected override void OnInitialized(EventArgs e)
{
InitializeComponent();
base.OnInitialized(e);
this._button.Content = _btn.Content;
this._button.Background = _btn.Background;
this.Width = _btn.Width;
this.Height = _btn.Height;
}
}
It is going to work undoubtly.

Another Option based on #Funk's answer is to make a content control instead of a button on the template, then bind the content control's content to your ButtonProperty in the code behind:
on the template:
<ContentControl Content={Binding myButton} Width="200" Height="100"/>
in the template code behind:
public static readonly DependencyProperty myButtonProperty =
DependencyProperty.Register("Button", typeof(Button), typeof(Template),
new UIPropertyMetadata(new PropertyChangedCallback(ButtonChangedCallback)));
and then on the Main Window:
<Window.Resources>
<Button x:Key="UserButton"
Background="Yellow"
Content="Actual Button"
/>
</Window.Resources>
<Grid>
<templateCode:Template myButton="{StaticResource UserButton}"/>
</Grid>
The nice thing about this is that Visual Studio is smart enough to show this code at design time, as well as having less code overall.
You can set things constant things (like location, font, and coloring) for your button either on the content control or in a default style, and then modify just the parts you need for you button.

One option is to simply start writing C# on the xaml page using < ![CDATA[ *** ]]>
In the Main Window.xaml you change to:
<templateCode:Template x:Name="test">
<x:Code><![CDATA[
Void OnStartup()
{
test.MyButton.Content="Actual Button";
test.MyButton.Background = new SolidColorBrush(Color.FromArgb(255,255,255,0));
}
]]>
</x:Code>
Then right after Initialize Object() you call OnStartup().
Although this does let you edit specific properties in the xaml, this is about the same as just writing the code in the code behind, where others expect it to be.

defining bindings for elements in a collection in xaml wont work

i have a simple Control with a collection of elements. I want to add elements in xaml and bind to the element.
However when i bind to Bar.Value in xaml it never works. Minimal example:
[ContentProperty("Bars")]
public class FooControl : Control
{
private ObservableCollection<IBar> _bars = new ObservableCollection<IBar>();
public ObservableCollection<IBar> Bars { get { return _bars; } }
}
public interface IBar
{
string Value { get; }
}
public class Bar : DependencyObject, IBar
{
public static readonly DependencyProperty ValueProperty = DependencyProperty.Register("Value", typeof(string), typeof(Bar), new PropertyMetadata("<not set>"));
public string Value
{
get { return (string)GetValue(ValueProperty); }
set { SetValue(ValueProperty, value); }
}
}
<Window x:Class="WpfTestApplication.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:this="clr-namespace:WpfTestApplication"
xmlns:sys="clr-namespace:System;assembly=mscorlib"
Title="MainWindow" Height="200" Width="1000">
<Window.Resources>
<Style TargetType="this:FooControl">
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="this:FooControl">
<ItemsControl ItemsSource="{Binding Bars, RelativeSource={RelativeSource TemplatedParent}}">
<ItemsControl.ItemTemplate>
<DataTemplate>
<TextBlock Text="{Binding Value}"/>
</DataTemplate>
</ItemsControl.ItemTemplate>
</ItemsControl>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
</Window.Resources>
<Window.DataContext>
<sys:String>from DataContext</sys:String>
</Window.DataContext>
<Grid>
<this:FooControl>
<this:Bar Value="directly set"/>
<this:Bar Value="{Binding Source=from_binding_source}"/>
<this:Bar Value="{Binding}"/>
<this:Bar Value="{Binding Text, ElementName=SomeTextBlock}"/>
</this:FooControl>
<TextBlock Text="from TextBox" Name="SomeTextBlock" Visibility="Collapsed"/>
</Grid>
</Window>
output
directly set
from_binding_source
"<not set>"
"<not set>"
debug output
System.Windows.Data Error: 2 : Cannot find governing FrameworkElement or FrameworkContentElement for target element. BindingExpression:Path=Text; DataItem=null; target element is 'Bar' (HashCode=26568931); target property is 'Value' (type 'String')
Any suggestion how to get it to work?
My current workaround is to define the bindings in code but this is a lot more code and looking at the xaml its not obvious which bindings do exists. (see my answer for workaround code)

dont know if this helps but
[ContentProperty("Bars")]
public class FooControl : Control
{
private ObservableCollection<object> _bars = new ObservableCollection<object>();
public ObservableCollection<object> Bars { get { return _bars; } }
}
xaml
<this:FooControl>
<this:Bar Value="directly set"/>
<this:Bar Value="{Binding Source=from_binding_source}"/>
<TextBlock Text="{Binding}"/>
<TextBlock Text="{Binding Text, ElementName=SomeTextBlock}"/>
</this:FooControl>
you get your desired result

my workaround so far
<this:Bar x:Name="bar3" />
<this:Bar x:Name="bar4" />
void MainWindow_Loaded(object sender, RoutedEventArgs e)
{
var bar3 = (DependencyObject)FindName("bar3");
BindingOperations.SetBinding(bar3, Bar.ValueProperty, new Binding("DataContext") { Source = this });
var bar4 = (DependencyObject)FindName("bar4");
BindingOperations.SetBinding(bar4, Bar.ValueProperty, new Binding("Text") { Source = FindName("SomeTextBlock") });
}

My WPF custom control's Data Context is superseding parent's

In my main window, I try to bind to a bool, but it's looking in my custom control's DataContext instead. If I don't assign DataContext in the user control, then the main window's bindings works, but (obviously) this brakes the bindings in the user control.
Here's the error:
System.Windows.Data Error: 40 : BindingExpression path error: 'MyControlVisible' property not found on 'object' ''MyUserControlModel' (HashCode=1453241)'. BindingExpression:Path=MyControlVisible; DataItem='MyUserControlModel' (HashCode=1453241); target element is 'MyUserControl' (Name='_myUserControl'); target property is 'Visibility' (type 'Visibility')
I need binding to work on both controls, but I don't want the user control's DataContext to supersede the window's.
Here's the code:
<Window x:Class="Sandbox.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:Controls="clr-namespace:Sandbox.Controls" Title="Sandbox">
<DockPanel LastChildFill="True">
<DockPanel.Resources>
<BooleanToVisibilityConverter x:Key="boolToVis" />
</DockPanel.Resources>
<Grid>
<Controls:MyUserControl x:Name="_myUserControl" Visibility="{Binding MyControlVisible, Converter={StaticResource boolToVis}}"/>
</Grid>
</DockPanel>
</Window>
namespace Sandbox
{
public partial class MainWindow
{
private MainWindowModel model;
public MainWindow()
{
InitializeComponent();
DataContext = model = new MainWindowModel();
_myUserControl.Initialize(model.MyUControlModel);
}
}
}
using System.ComponentModel;
using Sandbox.Controls;
namespace Sandbox
{
public class MainWindowModel : BaseModel
{
public MyUserControlModel MyUControlModel { get; set; }
public bool MyControlVisible { get; set; }
public MainWindowModel()
{
MyUControlModel = new MyUserControlModel();
MyControlVisible = false;
OnChange("");
}
}
public class BaseModel : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
protected void OnChange(string s)
{
var handler = PropertyChanged;
if (handler != null)
{
handler(this, new PropertyChangedEventArgs(s));
}
}
}
}
<UserControl x:Class="Sandbox.Controls.MyUserControl"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
mc:Ignorable="d">
<Grid>
<TextBlock Text="{Binding MyBoundText}"/>
</Grid>
</UserControl>
namespace Sandbox.Controls
{
public partial class MyUserControl
{
public MyUserControl()
{
InitializeComponent();
}
public void Initialize(MyUserControlModel context)
{
DataContext = context;
}
}
}
namespace Sandbox.Controls
{
public class MyUserControlModel : BaseModel
{
public string MyBoundText { get; set; }
public MyUserControlModel()
{
MyBoundText = "Hello World!";
OnChange("");
}
}
}

That is one of the many reasons you should never set the DataContext directly from the UserControl itself.
When you do so, you can no longer use any other DataContext with it because the UserControl's DataContext is hardcoded in.
In the case of your binding, normally the DataContext would be inherited so the Visibility binding could find the property MyControlVisible on the current DataContext, however because you hardcoded the DataContext in your UserControl's constructor, that property is not found.
You could specify a different binding source in your binding, such as
<Controls:MyUserControl Visibility="{Binding
RelativeSource={RelativeSource AncestorType={x:Type Window}},
Path=DataContext.MyControlVisible,
Converter={StaticResource boolToVis}}" ... />
However that's just a workaround for the problem for this specific case, and in my view is not a permanent solution. A better solution is to simply not hardcode the DataContext in your UserControl
There are a few different ways you can do depending on your UserControl's purpose and how your application is designed.
You could create a DependencyProperty on your UserControl to pass in the value, and bind to that.
<Controls:MyUserControl UcModel="{Binding MyUControlModelProperty}" ... />
and
<UserControl x:Class="Sandbox.Controls.MyUserControl"
ElementName=MyUserControl...>
<Grid DataContext="{Binding UCModel, ElementName=MyUserControl}">
<TextBlock Text="{Binding MyBoundText}"/>
</Grid>
</UserControl>
Or you could build your UserControl with the expectation that a specific property will get passed to it in the DataContext. This is normally what I do, in combination with DataTemplates.
<Controls:MyUserControl DataContext="{Binding MyUControlModelProperty}" ... />
and
<UserControl x:Class="Sandbox.Controls.MyUserControl"...>
<Grid>
<TextBlock Text="{Binding MyBoundText}"/>
</Grid>
</UserControl>
As I said above, I like to use DataTemplates to display my UserControls that expect a specific type of Model for their DataContext, so typically my XAML for the main window would look something like this:
<DataTemplate DataType="{x:Type local:MyUControlModel}">
<Controls:MyUserControl />
</DataTemplate>
<ContentPresenter Content="{Binding MyUControlModelProperty}" ... />

Changing View on Buttonclick

I am learning WPF and MVVM at the moment (or at least I am trying to...).
I created a little sample-app, that shows a Window with 2 buttons, each of it should show a new View on Click. So I created 3 UserControls (DecisonMaker with the 2 Buttons, and one Usercontrol for each "clicktarget").
So I bound the CotentControl of the MainWindow to a property called "CurrentView" in my MainWindowViewModel
Code of MainWindow.xaml:
<Window x:Class="WpfTestApplication.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="clr-namespace:WpfTestApplication"
Title="MainWindow" Height="350" Width="525">
<Window.DataContext>
<local:MainWindowViewModel />
</Window.DataContext>
<Grid>
<ContentControl Content="{Binding CurrentView, Mode=OneWay}" />
</Grid>
</Window>
Code of MainWindowViewModel:
class MainWindowViewModel
{
private UserControl _currentView = new DecisionMaker();
public UserControl CurrentView
{
get { return _currentView; }
set { _currentView = value; }
}
public ICommand MausCommand
{
get { return new RelayCommand(LoadMouseView); }
}
public ICommand TouchCommand
{
get { return new RelayCommand(LoadTouchView); }
}
private void LoadMouseView()
{
CurrentView = new UserControlMouse();
}
private void LoadTouchView()
{
CurrentView = new UserControlTouch();
}
}
The initial UserControl (DecisionMaker) shows up as supposed. Also the method LoadMouseView is called. But the View doesn't change. What am I missing?
UPDATE: Thanks so much! I missed the INotifyPropertyChanged-interface. All of your answers were just great and very accurate and helpful! I don't know which one to accept - I think it's the most fair way to accept the "first" answer?
I accepted blindmeis answer, as it solved the problem and helped me understand MVVM better. But every answer was really great thanks to all of you!

if you wanna do mvvm - then you should have no references to your view/usercontrols in your viewmodel. you have to implement INotifyPropertyChanged! ps: if you need System.Windows namespace in your Viewmodel - then something is wrong.
in your case what you need:
1 mainviewmodel
1 viewmodel for UserControlMouse
1 viewmodel for UserControlTouch
1 view/usercontrol for UserControlMouse
1 view/usercontrol for UserControlTouch
your mainviewmodel should have at least 2commands to switch your view and 1 property for CurrentView. in your command you simply set your CurrentView to the right viewmodel instance. at least you need two datatemplates for each viewmodel which define the right view.
public object CurrentView
{
get { return _currentView; }
set {
_currentView = value; this.RaiseNotifyPropertyChanged("CurrentView");}
}
xaml
<Window x:Class="WpfTestApplication.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="clr-namespace:WpfTestApplication"
Title="MainWindow" Height="350" Width="525">
<Window.Resources>
<DataTemplate DataType="{x:Type local:MyMouseViewModel}">
<local:MyMouseUserControlView/>
</DataTemplate>
<DataTemplate DataType="{x:Type local:MyTouchViewModel}">
<local:MyTouchUserControlView/>
</DataTemplate>
</Window.Resources>
<Window.DataContext>
<local:MainWindowViewModel />
</Window.DataContext>
<Grid>
<!-- here your buttons with command binding, i'm too lazy to write this. -->
<!-- you content control -->
<ContentControl Content="{Binding CurrentView, Mode=OneWay}" />
</Grid>
</Window>

I would do something like this to select the input style that you want, to MainWindow I've added a property that lets me select the mode of input.
public enum UserInterfaceModes
{
Mouse,
Touch,
}
public UserInterfaceModes UserInterfaceMode
{
get { return (UserInterfaceModes)GetValue(UserInterfaceModeProperty); }
set { SetValue(UserInterfaceModeProperty, value); }
}
public static readonly DependencyProperty UserInterfaceModeProperty = DependencyProperty.Register("UserInterfaceMode", typeof(UserInterfaceModes), typeof(MainWindow), new UIPropertyMetadata(UserInterfaceModes.Mouse));
then for the xaml view part you can select the correct template with a trigger.
<Style TargetType="{x:Type local:MainWindow}">
<Style.Triggers>
<DataTrigger Binding="{Binding UserInterfaceMode}" Value="Mouse">
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type local:MainWindow}">
<Grid Background="Red"/>
</ControlTemplate>
</Setter.Value>
</Setter>
</DataTrigger>
<DataTrigger Binding="{Binding UserInterfaceMode}" Value="Touch">
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type local:MainWindow}">
<Grid Background="Blue"/>
</ControlTemplate>
</Setter.Value>
</Setter>
</DataTrigger>
</Style.Triggers>
</Style>

The viewmodel need to implement INotifyPropertyChanged. Otherwise the view won't be notified when a property changes in the viewmodel.
class MainWindowViewModel : INotifyPropertyChanged
{
private UserControl _currentView = new DecisionMaker();
public UserControl CurrentView
{
get { return _currentView; }
set
{
_currentView = value;
OnPropertyChanged("CurrentView");
}
}
public event PropertyChangedEventHandler PropertyChanged;
private void OnPropertyChanged(string propertyName)
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
}
}

You need to implement INotifyPropertyChanged on MainWindowViewModel, such that the view is informed when the CurrentView property is changed.

It sounds like the behaviour you want is pretty much what you get with a [TabControl][1] - why not use this built in control and just bind the DataContext of both tabs to the same view model.
This also has the advantage that your view model wouldn't know about the view classes (I am assuming that UserControlMouse etc are user controls).
Note: this will not be applicable if you need the view model to be aware of whether it is in touch or mouse mode.