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.
Related
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
I have 2 main classes. The first class represents a Cell that can have values X, O or Empty. I have implemented INotifyPropertyChanged on this.
public class Cell : INotifyPropertyChanged
{
private Symbol state;
public Symbol State
{
get { return state; }
set
{
if (value == Symbol.X || value == Symbol.O)
state = value;
OnPropertyChanged("State");
}
}
public Cell()
{
state = Symbol.Empty;
}
public enum Symbol
{
X, O, Empty
}
public event PropertyChangedEventHandler PropertyChanged;
private void OnPropertyChanged(string propName)
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(propName));
}
}
}
The second class contains an object of this class and is also set as the datacontext for my main window.
public class Board
{
private Cell testCell;
public Cell TestCell
{
get { return testCell; }
set { testCell = value; }
}
public Board()
{
TestCell = new Cell();
}
public void Cell_Click(int cellNum)
{
TestCell.State = Cell.Symbol.O;
}
}
In my mainwindow I have set the datacontext as board, and also contains a button_click function.
public partial class MainWindow : Window
{
public MainWindow()
{
InitializeComponent();
this.DataContext = new Board();
}
private void Button_Click(object sender, RoutedEventArgs e)
{
Board board = this.DataContext as Board;
board.Cell_Click(cellNum);
}
}
In my XAML I have bound to Cell object within board using a button style like this:
<Setter Property="Background" Value="{Binding TestCell,
Converter={StaticResource BGConverter}}"/>
BGConverter is a custom converter that accepts a Cell object and converts it into a Colors object. I believe I am indeed directly binding to an object that has INotify implemented, so there's no issue of nested objects. However the binding doesn't reflect changes when I click. When debugging, I found that PropertyChanged event is always null.
The closest answer I found for this is that the event will be subscribed to only if the class Cell is my datacontext. Atleast that's what I understood. How can I correct this problem?
Also I am fresh out of college, currently learning WPF on a new job, so any general recommendations are welcome too.
Thanks
Simply bind to TestCell.State instead of TestCell
I'm pretty new at this myself, but I believe your data context needs to implement INotifyPropertyChanged as well.
That is, your Board class needs to listen to the PropertyChanged event of the cells and fire its own PropertyChanged event when this happens.
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
Hi i am trying to use the NotifyPropertyChanged to update all the places where i am binding a property. For what i have searched the INotifyPropertyChanged is indicated to this cases.
So i need help because i don't understand what i have wrong in here. And i really don't know what to do with the PropertyChange event. My question about that is, when he changes? What i have to more with him?
Datagrid:
<ListView Name="listView" ItemsSource="{Binding Categories}"/>
An example when i change my Categories property:
DataTest dtTest = new DataTest();
public MainWindow()
{
InitializeComponent();
this.DataContext = dtTest;
}
private void Button1_Click(object sender, RoutedEventArgs e)
{
//Here i pick up a string from a textBox, where i will insert in a Table of my DB,
//Then i will do a query to my Table, and i will get a DataTable for example
//Then i just put the contents into the DataView, so the value have changed.
dtTest.Categories = dtTable.DefaultView;
dtTest = dtTable.defaultView; (this only an example, i don't this for real.)
//What i have to do now, to wherever i am binding (DataGrid, ListView, ComboBox)
//the property to the new values automatically being showed in all places?
}
My Class:
public class DataTest : INotifyPropertyChanged
{
private DataView categories;
public event PropertyChangedEventHandler PropertyChanged; //What i have to do with this?
private void NotifyPropertyChanged(string str)
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(str));
}
}
public DataView Categories
{
get { return categories; }
set
{
if (value != categories)
{
categorias = value;
NotifyPropertyChanged("Categories");
}
}
}
}
My Class with INotifyCollectionChanged:
public class DataTest : INotifyCollectionChanged
{
public event NotifyCollectionChangedEventHandler CollectionChanged;
private void OnCollectionChanged(NotifyCollectionChangedEventArgs e)
{
if (CollectionChanged != null)
{
CollectionChanged(this, e);
}
}
public DataView Categories
{
get { return categories; }
set
{
if (value != categories)
{
categories = value;
OnCollectionChanged(new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Add, Categories));
}
}
}
}
But why the PropertyChanged is always NULL??? I have to do something more, but i don't know what.
Thanks in advance!
the DataTest class needs to be the DataContext for the Binding. You can set this in code-behind (or a myriad of other ways, but for simplicity - just do it in code-behind)
public MainWindow() // constructor
{
this.DataContext = new DataTest();
}
Then, with the 'Source' of the Binding set, you can specify the 'Path', so your xaml looks like this:
<ListBox ItemsSource="{Binding Categories}" />
Now, if the property 'Categories' is changed in code, the NotifyPropertyChanged code you have written will alert the Binding, which in turn will access the public getter for the property and refresh the view.
Getting the handler prevents the event handler from going to null after you check for null and checking for null will prevent you from getting a null exception if there are no event handlers.
The reason that your PropertyChanged is null is that there are no event handlers attached to it. The reason there are not handlers attached to it is you have not bound your object to anything (which will take care of adding a handler) or you haven't added a handler to it (if you wanted to observe it for some other reason). Once your object is created you need to bind it somewhere.
You are doing all you have to do. An event is just a special kind of delegate. You declare it, you invoke it, clients subscribe to it. That's all there is to it.
say I have this control:
public partial class bloc999 : UserControl
{
bloc999Data mainBlock = new bloc999Data();
public bloc999()
{
InitializeComponent();
mainBlock.txtContents = "100";
base.DataContext = mainBlock;
}
}
in the xaml:
<TextBox Margin="74,116,106,0" Name="txtContents"
Text="{Binding Path=txtContents, UpdateSourceTrigger=PropertyChanged,Mode = TwoWay}" />
<TextBox Margin="74,145,106,132" Name="txtContents2"
Text="{Binding Path=txtContents2, UpdateSourceTrigger=PropertyChanged,Mode = TwoWay}" />
Then I have this class:
public class bloc999Data : INotifyPropertyChanged
{
string _txtContents;
string _txtContents2;
public event PropertyChangedEventHandler PropertyChanged;
void NotifyPropertyChanged(string propName)
{
if (this.PropertyChanged != null)
this.PropertyChanged(
this, new PropertyChangedEventArgs(propName));
}
public string txtContents2
{
get
{
return this._txtContents2;
}
set
{
if (int.Parse(value) > int.Parse(this._txtContents))
{
this._txtContents2 = "000";
}
else
this._txtContents2 = value;
NotifyPropertyChanged("txtContents2");
}
}
public string txtContents
{
get
{
return this._txtContents;
}
set
{
this._txtContents = value;
NotifyPropertyChanged("txtContents");
}
}
}
Ok now say I have A button on the form and I do this in the code:
mainBlock.txtContents2 = "7777777";
It puts 000 in the textbox, but If i just type in manually, in the textbox (txtContents2), the setter code is called but for some reason the textboxes value does not change, the instance value does change. help?
I believe it's just because the value is changing within the context of the data binding operation, so WPF just ignores it because it knows the value is changing and thinks the event is superfluous. What it doesn't know is that you've gone and changed the value from the value WPF has to something else again.
If you do the notification in a separate message then WPF will process it outside the context of the current data binding operation and will thus pick up the change:
if (int.Parse(value) > int.Parse(this._txtContents))
{
this._txtContents2 = "000";
// notify WPF of our change to the property in a separate message
Dispatcher.BeginInvoke((ThreadStart)delegate
{
NotifyPropertyChanged("txtContents2");
});
}
else
{
this._txtContents2 = value;
NotifyPropertyChanged("txtContents2");
}
This assumes your view model has access to the Dispatcher. An example of how to do so is shown in my blog post on a base ViewModel class.
I was having similar problem earlier here
In your usercontrol, update Binding and set UpdateSourceTrigger to Explicit
<TextBox Margin="74,145,106,132" x:Name="txtContents2" TextChanged="txtContents2_TextChanged"
Text="{Binding Path=txtContents2, UpdateSourceTrigger=Explicit,Mode = TwoWay}" />
then in the TextChanged event handler update the binding manually by validating the input.
move validation logic from property txtContent2's setter in bloc999Data in this event handler
private void txtContents2_TextChanged(object sender, TextChangedEventArgs e)
{
if (int.Parse(txtContents2.Text) > int.Parse(mainBlock.txtContents))
{
mainBlock.txtContents2 = "000";
txtContents2.GetBindingExpression(TextBox.TextProperty).UpdateTarget();
}
else
{
mainBlock.txtContents2 = txtContents2.Text;
txtContents2.GetBindingExpression(TextBox.TextProperty).UpdateSource();
}
}
and it works.
Hope it helps!!