WPF -- simple checkbox binding question

Question

Hello,

While it is trivial to store a checkbox's checked state in a variable using the checkbox's Click event, how would I do it via databinding? All the examples I have found have the UI updated from some datasource, or bind one control to another; I want to update a member variable when the checkbox is clicked.

TIA for any pointers...

Answer 1

if you have the property "MyProperty" on your data-class, then you bind the IsChecked like this.... (the converter is optional, but sometimes you need that)

<Window.Resources>
<local:MyBoolConverter x:Key="MyBoolConverterKey"/>
</Window.Resources>
<checkbox IsChecked="{Binding Path=MyProperty, Converter={StaticResource MyBoolConverterKey}}"/>

Answer 2

You must make your binding bidirectional :

<checkbox IsChecked="{Binding Path=MyProperty, Mode=TwoWay}"/>

Answer 3

You need a dependency property for this:

public BindingList<User> Users
     {
      get { return (BindingList<User>)GetValue(UsersProperty); }
      set { SetValue(UsersProperty, value); }
     }

     public static readonly DependencyProperty UsersProperty =
      DependencyProperty.Register("Users", typeof(BindingList<User>), typeof(OptionsDialog));

Once that done, you bind the checkbox to the dependency property:

<CheckBox x:Name="myCheckBox" IsChecked="{Binding ElementName=window1, Path=CheckBoxIsChecked}" />

For that to work you have to name your Window or UserControl in its openning tag, and use that name in the ElementName parameter.

Whit this code, when ever you change the property on the code side will change the textbox, and whenever you check/uncheck the textbox, the Dependency Property will change too.

EDIT:

An easy way to create a dependency property is typing the snippet propdp, which will give you the general code for Dependency Properties.

All the code:

XAML:

<Window x:Class="StackOverflowTests.Window1"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="Window1" x:Name="window1" Height="300" Width="300">
    <Grid>
     <StackPanel Orientation="Vertical">
      <CheckBox Margin="10" x:Name="myCheckBox" IsChecked="{Binding ElementName=window1, Path=IsCheckBoxChecked}">Bound CheckBox</CheckBox>
      <Label Content="{Binding ElementName=window1, Path=IsCheckBoxChecked}" ContentStringFormat="Is checkbox checked? {0}"></Label>
     </StackPanel>  
    </Grid>
</Window>

C#:

using System.Windows;

namespace StackOverflowTests
{
    /// <summary>
    /// Interaction logic for Window1.xaml
    /// </summary>
    public partial class Window1 : Window
    {
     public bool IsCheckBoxChecked
     {
      get { return (bool)GetValue(IsCheckBoxCheckedProperty); }
      set { SetValue(IsCheckBoxCheckedProperty, value); }
     }

     // Using a DependencyProperty as the backing store for IsCheckBoxChecked.  This enables animation, styling, binding, etc...
     public static readonly DependencyProperty IsCheckBoxCheckedProperty =
      DependencyProperty.Register("IsCheckBoxChecked", typeof(bool), typeof(Window1), new UIPropertyMetadata(false));

     public Window1()
     {
      InitializeComponent();
     }
    }
}

Notice how the only code behind is the Dependency Property. Both the label and the checkbox are binded to it. If the checkbox changes it, the label changes too.