Im trying to make a WPF based program that will read the textbox input (user input) from a usercontrol and save it as a object proprety. The usercontrol is added to MainWindow. From MainWindow, you have a button which displays a message box with the textbox value. I'm not sure how to connect it all.
Error = CS0103 The name 'minJpValue' does not exist in the current
context WpfApp1
Please help
(Usercontrol .xaml code)
<TextBox x:Name="minJpValue"/>
(Custom class)
public class jpData
{
public double minJpValue
{
get { return minJpValue; }
set { minJpValue = value; }
}
}
(MainWindow .cs code)
private void clickclick(object sender, RoutedEventArgs e)
{
MessageBox.Show(minJpValue);
}
The issue can be easily fixed using the MVVM Patterns,
The code for the usercontrol will be similar to this
<Grid Background="Red">
<TextBox x:Name="minJpValue" Text="{Binding Path=minJpValue}" />
</Grid>
Create new ViewModel for the MainWindow as follows
public class MainWindowViewModel : INotifyPropertyChanged
{
/// <summary>
/// Property Changed Event Handler
/// </summary>
public event PropertyChangedEventHandler PropertyChanged;
// Create the OnPropertyChanged method to raise the event
protected void OnPropertyChanged(string name)
{
PropertyChangedEventHandler handler = PropertyChanged;
if (handler != null)
{
handler(this, new PropertyChangedEventArgs(name));
}
}
private String _minJpValue;
public String minJpValue {
get { return _minJpValue; }
set {
_minJpValue = value;
OnPropertyChanged(nameof(minJpValue));
}
}
}
Add the usercontrol into your MainWindow view and in the codebehind set the datacontext to the ViewModel as follows
public MainWindowViewModel CurrentModel = new MainWindowViewModel();
public MainWindow()
{
InitializeComponent();
this.DataContext = CurrentModel;
}
private void Button_Click(object sender, RoutedEventArgs e)
{
MessageBox.Show(CurrentModel.minJpValue);
}
This can solve your current problem. Please see that its working as per expected.
For this quick fix use:
MessageBox.Show(minJpValue.Text);
But a better way would be to store the value on a VM (View Model) and bind the control to it using the MVVM pattern. I provide a basic example on
Xaml: ViewModel Main Page Instantiation and Loading Strategy for Easier Binding
Ok let's Understand wt have u done wrong.
<TextBox Name="minJpValue"/>
This line of will Create an object for TextBox and the object will be referred with ur name
minJpValue as u mentioned this will be inside another Usercontrol object and u r try to minJpValue in MainWindow how does it even know that something like minJpValue this exists
So Here is the answer:
objjpData.minJpValue = minJpValue.Text;//Inside user control when ever u change the `minJpValue` u need to set it too bjjpData.minJpValue
pass this objjpData to mainwindow or where u wanna acesses then
MessageBox.Show(objjpData.minJpValue);
Option 2:
MessageBox.Show(UserControlObject.minJpValue.Text);
And PS: Check MVVM once
Related
My app has to load a .txt file from the file system, read it and put its text into a TextBlock, but I don't know how to connect my Button to my view model so my text block that is bound to a property in it displays this text.
Let's repeat what I want my app to do:
A user clicks on the load button and he chooses a .txt file
The text from the file is assigned to the NumbersString property
The text block loads this text from the NumbersString property
I dont know how to get step 2 to work.
XAML
<Button Name="load" Background="Pink" Click="load_Click">Load File</Button>
<TextBox x:Name="numbers1" Text="{Binding NumbersString, UpdateSourceTrigger=PropertyChanged}" IsReadOnly="True"/>
Code-behind XAML
There is a mistake my view model property NumbersString. It should be connected to the button.
public partial class MainWindow : Window
{
public MainWindow()
{
InitializeComponent();
this.DataContext = new numbersViewModel();
}
public void load_Click(object sender, RoutedEventArgs e)
{
OpenFileDialog openFileDialog = new OpenFileDialog();
if (openFileDialog.ShowDialog() == true)
NumbersString = File.ReadAllText(openFileDialog.FileName);
}
}
View model
class numbersViewModel : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
private numbersModel _model;
protected void RaisePropertyChanged(string propertyName)
{
PropertyChangedEventHandler evt = PropertyChanged;
if (evt != null)
evt(this, new PropertyChangedEventArgs(propertyName));
}
// iI want my text block to take the string from here
public string NumbersString
{
get { return _model.numbersString; }
set
{
if (value != _model.numbersString)
{
_model.numbersString = value;
RaisePropertyChanged("numbers1");
}
}
}
}
Model
private string model="";
public string numbersString
{
get
{
return model;
}
set
{
model = value;
}
}
You raise the property changed event for numbers1 in your NumbersString property, therefore the change for the wrong property (that does not even exist) is triggered, but that will not update the TextBox.
Adapt the property name in the call to RaisePropertyChanged. You can use nameof instead of a hardcoded string.
public string NumbersString
{
get { return _model.numbersString; }
set
{
if (value != _model.numbersString)
{
_model.numbersString = value;
RaisePropertyChanged(nameof(NumbersString));
}
}
}
Since you are using a mix of code-behind and MVVM, you could set the NumbersString property in your event handler like this:
public void load_Click(object sender, RoutedEventArgs e)
{
OpenFileDialog openFileDialog = new OpenFileDialog();
if (openFileDialog.ShowDialog() == true)
((numbersViewModel)DataContext).NumbersString = File.ReadAllText(openFileDialog.FileName);
}
The last bit to make it work is that you never create or assign an instance of a numbersModel to the _model property on numbersViewModel. You could do that in the constructor.
public numbersViewModel(numbersModel numbersModel)
{
_model = numbersModel;
}
An MVVM approach using commands
Instead of using event handlers for button clicks, you should use commands. You can copy the RelayCommand class that #aepot linked. First, you create an ICommand property in your numbersViewModel.
public ICommand LoadFile { get; }
RelayCommand implements the ICommand interface and delegates the execution logic to a method that you have to pass when creating it in the constructor of numbersViewModel:
public numbersViewModel(numbersModel numbersModel)
{
_model = numbersModel;
LoadFile = new RelayCommand(ExecuteLoadFile);
}
The ExecuteLoadFile method contains the logic for loading the file and reading its text. In practice, this would also violate MVVM priciples as this method is located in a view model and OpenFileDialog is a view type. You would extract this part into a service with an interface, so that the view model does not know about its implementation, but that is beyond the scope of this question.
private void ExecuteLoadFile(object obj)
{
var openFileDialog = new OpenFileDialog();
if (openFileDialog.ShowDialog().GetValueOrDefault())
NumbersString = File.ReadAllText(openFileDialog.FileName);
}
Finally, bind the Command property on your button to the LoadFile command.
<Button Name="load" Background="Pink" Content="Load File" Command="{Binding LoadFile}"/>
With these changes you can remove the event handler from your MainWindow.
I have a UserControl Person_UC and Student_UC. There is a ComboBox in Student_UC which I want to disable it from Person_UC.
But its not working. I want to accomplish this without MVVM.
public partial class Person_UC : UserControl
{
public Person_UC()
{
InitializeComponent();
Student_UC su = new Student_UC();
su.myComboBoxName.IsEnabled = false;
}
}
Without MVVM it would be quite hard to solve. You have to manipulate the same instance of Student_UC which is currently used.
Actually, you're instantiating a new Student_UC and disabling its ComboBox, but you're not doing anything with your variable "su". Did you assign it somewhere?
Basically, you should have one ViewModel per UserControl, so a ViewModel for Person_UC and a ViewModel for Student_UC.
Warning, this solution requires you to use a MVVM Framework like MVVM Light (https://mvvmlight.codeplex.com) for sending messages.
One standard way would be sending a message. Bind your Loaded event of your Person_UC to a method in your code-behind like so:
<UserControl x:Class="YourAssembly.Person_UC"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Name="Person_UC"
Loaded="Loaded">
<Grid Name="RootGrid">
</Grid>
</UserControl>
And:
public partial class Person_UC : UserControl
{
public Person_UC()
{
InitializeComponent();
}
private void Loaded(object sender, RoutedEventArgs e)
{
//Use a Message to notify your Student_UC's ViewModel that you would like to disable its ComboBox
Messenger.Default.Send<ChangeComboBoxEnabilityMessage>(new ChangeComboBoxEnabilityMessage(false));
}
}
Then, when you receive the message within the Student_UC's ViewModel, you have to pass this information to the view. Basically, you can bind IsEnable property of the ComboBox to a property in its ViewModel, that you will set to false when the message is received.
public class Student_UC_ViewModel : INotifyPropertyChanged
{
public Student_UC_ViewModel()
{
//Register your message
Messenger.Default.Register<ChangeComboBoxEnabilityMessage>(message => ComboBoxIsEnabled = message.ComboBoxIsEnabled);
}
private bool _comboBoxIsEnabled;
public bool ComboBoxIsEnabled
{
get
{
return _comboBoxIsEnabled;
}
set
{
_comboBoxIsEnabled = value;
OnPropertyChanged("ComboBoxIsEnabled");
}
}
public event PropertyChangedEventHandler PropertyChanged;
protected void OnPropertyChanged(string name)
{
PropertyChangedEventHandler handler = PropertyChanged;
if (handler != null)
{
handler(this, new PropertyChangedEventArgs(name));
}
}
}
And your message class:
public class ChangeComboBoxEnabilityMessage : MessageBase
{
public ChangeComboBoxEnabilityMessage(bool comboBoxEnabled)
{
ComboBoxIsEnabled = comboBoxEnabled;
}
public bool ComboBoxIsEnabled
{
get;
set;
}
}
I let you bind your IsEnable property of your ComboBox in your Student_UC xaml to the property of its ViewModel (i.e ComboBoxIsEnabled).
Don't forget to make sure your DataContext is set:
public partial class Student_UC : UserControl
{
public Person_UC()
{
InitializeComponent();
DataContext = new Student_UC_ViewModel();
}
...
}
Also, take care of your binding issues, see your output console in Visual Studio.
I am just starting with WPF and I am trying to setup binding between a local variable and a label. Basicaly I want to update the label when local variable changes. I was searching for solution but they all just use textbox as a source not just class variable and I am not even sure it works this way. So here is my code.
public partial class MainWindow : Window
{
int idCounter;
public MainWindow()
{
InitializeComponent();
Binding b = new Binding();
b.Source = idCounter;
b.Mode = BindingMode.OneWay;
b.UpdateSourceTrigger = UpdateSourceTrigger.PropertyChanged;
myLabel.SetBinding(Label.ContentProperty,b);
}
private void Button_Click(object sender, RoutedEventArgs e)
{
idCounter++;
}
}
Button does work, idCounter changes value, but it does not update in label so I guess binding is wrong. Can someone tell me what is wrong? Thanks
Your code will work if you change your class to this...
public partial class Window1 : Window, INotifyPropertyChanged
{
private int _idCounter;
public int IdCounter
{
get { return _idCounter; }
set
{
if (value != _idCounter)
{
_idCounter = value;
OnPropertyChanged("IdCounter");
}
}
}
public Window1()
{
InitializeComponent();
myLabel.SetBinding(ContentProperty, new Binding("IdCounter"));
DataContext = this;
}
private void Button_Click(object sender, RoutedEventArgs e)
{
e.Handled = true;
IdCounter++;
}
#region INotifyPropertyChanged Implementation
public event PropertyChangedEventHandler PropertyChanged;
protected virtual void OnPropertyChanged(string name)
{
var handler = System.Threading.Interlocked.CompareExchange(ref PropertyChanged, null, null);
if (handler != null)
{
handler(this, new PropertyChangedEventArgs(name));
}
}
#endregion
}
Some of the issues you were having are...
The window itself should implement INotifyPropertyChanged so that the binding engine can place an ear on it.
the IdCounter needs to be public and have a public getter on it so that the binding engine can 'get' it.
You should set the DataContext to whatever class has declared IdCounter (the MainWindow in this case). Part of the problem was that the binding engine had no DataContext.
The BindingMode setting was a red-herring since a Label binds that way by default.
The UpdateSourceTrigger was a red-herring since the content of the label does not have a mechanism to update the source property. A label's content is not like a text box where the user can type something that the code needs to know about. When you're binding to something that the user cannot change, forget about UpdateSourceTrigger, it's the Target property that counts.
The handler should mark the event. This is good practice and did not affect the binding.
The binding constructor needs only the path.
This code will give you your expected result; i.e., that the label updates when the button is clicked. Checked, compiled, and executed on vs2013, .net 4.5.
The other respondents said you should use a View Model. I agree with this 100%, and overall it's a good thing to consider.
You want to use a property to do this, as well as implementing INotifyPropertyChanged so that the label's content gets updated when the property changes.
Here's an example using a simple ViewModel
xaml:
<Window x:Class="WpfApplication1.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:converters="clr-namespace:WpfApplication1"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="MainWindow" Height="350" Width="525">
<StackPanel>
<Label Width="200" Height="50" Content="{Binding MyLabel}"/>
<Button Height="30" Width="100" Content="Increment" Click="Button_Click" />
</StackPanel>
</Window>
xaml.cs:
namespace WpfApplication1
{
/// <summary>
/// Interaction logic for MainWindow.xaml
/// </summary>
public partial class MainWindow : Window
{
MainViewModel vm = new MainViewModel();
public MainWindow()
{
InitializeComponent();
this.DataContext = vm;
}
private void Button_Click(object sender, RoutedEventArgs e)
{
vm.MyLabel += 1;
}
}
}
MainViewModel.cs:
namespace WpfApplication1
{
public class MainViewModel : INotifyPropertyChanged
{
#region Members
private int _myLabel;
#endregion Members
#region Properties
public int MyLabel
{
get
{
return _myLabel;
}
set
{
_myLabel = value;
NotifyPropertyChanged("MyLabel");
}
}
#endregion Properties
public MainViewModel()
{
}
#region INotifyPropertyChanged
public event PropertyChangedEventHandler PropertyChanged;
private void NotifyPropertyChanged(String propertyName)
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
}
#endregion
}
}
Note: Ideally, you would want to use a Command for the Button instead of a Click event handler
You cannot bind to something that is private or a field so convert it into public property. You can find more as to what is a valid binding source here
If you want changes to your property be picked up by UI you should implement INotifyPropertyChanged interface and raise event each time value of the property changes. So idCounter should look more like this:
private int _idCounter;
public int idCounter
{
get { return _idCounter; }
set
{
if (_idCounter != value)
{
_idCounter = value;
OnPropertyChanged("idCounter");
}
}
}
When you create binding to property you use Path
Binding works in binding context so you need to specify from where to take this Path. Easiest way to do that is to set DataContext. So in your case initialization should look more like this:
Binding b = new Binding("idCounter");
b.Mode = BindingMode.OneWay;
b.UpdateSourceTrigger = UpdateSourceTrigger.PropertyChanged;
myLabel.SetBinding(Label.ContentProperty, b);
DataContext = this;
As #d.moncada suggested in his answer you should create dedicated view model
I have a MainWindow that contains a text-block [statusTextblock] which has binding to a string [StatusText]. StatusTextblock needs to display combobox results from another window. I pass this data back to mainwindow when it changes in the other window and I've made a static method to change the string when this happens.
However, the staticness of all this leaves me unable to change my textbox element at any point to the new value of StatusText.
I thought about work arounds to bring the changes about when the user returned to Mainwindow but I've not succeeded. I tried the activate and uielement gotfocus event handler (i feel the 2nd one is still a possible fix).
Mainwindow also happens to be always open if that matters. I also prefer doing things in code than xaml, but would be grateful for any help.
Any ideas?
MainWindow xaml, then program entry method, then static event to change statusText
<TextBlock Margin="190,0,0,0" HorizontalAlignment="Right" Name="StatusTextBlock" Text= {Binding}" ></TextBlock>
public MainWindow() //Obviously more went here, but it's not relevent
{
StatusTextBlock.DataContext = statusText;
}
static public void changeStatusText(string status)
{
statusText = status;
}
The problem becomes simpler to solve when you try to implement the application using MVVM pattern.
Define a view model class which has a string property StatusText:
public class MainViewModel : INotifyPropertyChanged
{
private string _statusText;
public event PropertyChangedEventHandler PropertyChanged;
public string StatusText
{
get
{
return _statusText;
}
set
{
if (value == _statusText)
return;
_statusText = value;
if (PropertyChanged != null)
PropertyChanged(this, new PropertyChangedEventArgs("StatusText"));
}
}
}
Set the DataContext of the MainWindow to an instance of the MainViewModel:
public MainWindow //Obviously more went here, but it's not relevant
{
private static MainViewModel _mainViewModel = new MainViewModel();
public MainWindow()
{
this.DataContext = _mainViewModel;
}
static public void ChangeStatusText(string status)
{
_mainViewModel.StatusText = status;
}
}
Set the data binding to the view model:
<TextBlock Margin="190,0,0,0" HorizontalAlignment="Right" Name="StatusTextBlock" Text="{Binding StatusText}" ></TextBlock>
I am trying to implement data binding, and to have TextBox's text to be update once I click on some button.
XAML:
<TextBox Text="{Binding Path=Output}" />
Code:
public MainWindow()
{
InitializeComponent();
DataContext = Search;
Search.Output = "111";
}
public SearchClass Search = new SearchClass();
private void button1_Click(object sender, RoutedEventArgs e)
{
Search.Output = "222";
}
public class SearchClass
{
string _output;
public string Output
{
get { return _output; }
set { _output = value; }
}
}
When I execute the program, I see "111", so the binding from MainWindow() works, but if I click a button - the text in the TextBox is not updated (but in the debugger I see that button1_Click is executed and Search.Output is now equal to "222"). What am I doing wrong?
You should implement INotifyPropertyChanged in your SearchClass and then in setter raise the event:
public event PropertyChangedEventHandler PropertyChanged = delegate { };
public string Output
{
get { return _output; }
set
{
_output = value;
PropertyChanged(this, new PropertyChangedEventArgs("Output"));
}
}
If I understood right, SearchClass is the DataContext for your TextBlock. In this case implementing as above would help.
When WPF see some class as the source of Binding - it tries to cast it to INotifyPropertyChanged and subscribe to PropertyChanged event. And when event is raised - WPF updates the binding associated with sender (first argument of PropertyChanged). It is the main mechanism that makes binding work so smoothly.
You have to implement the INotifyPropertyChanged interface on your SearchClass class. This is how binder values are notified their source values have changed. It displays the "111" value because it hasn't been laid out yet (more or less), but will won't update after that until you implement that interface.