为什么我的WPF复选框绑定不工作？ [英] Why is my WPF CheckBox Binding not working?
问题描述
我使用MVVM，VS 2008和.NET 3.5 SP1。我有一个项目，每一个暴露IsSelected属性的列表。我已经添加了一个复选框来管理列表中的所有项目（更新每个项目的IsSelected属性）的选择/取消选择。一切除器isChecked物业工作不被在视图更新时PropertyChanged事件触发的CheckBox的绑定控件。
I'm using MVVM, VS 2008, and .NET 3.5 SP1. I have a list of items, each exposing an IsSelected property. I have added a CheckBox to manage the selection/de-selection of all the items in the list (updating each item's IsSelected property). Everything is working except the IsChecked property is not being updated in the view when the PropertyChanged event fires for the CheckBox's bound control.
<CheckBox
Command="{Binding SelectAllCommand}"
IsChecked="{Binding Path=AreAllSelected, Mode=OneWay}"
Content="Select/deselect all identified duplicates"
IsThreeState="True" />
我的VM：
My VM:
public class MainViewModel : BaseViewModel
{
public MainViewModel(ListViewModel listVM)
{
ListVM = listVM;
ListVM.PropertyChanged += OnListVmChanged;
}
public ListViewModel ListVM { get; private set; }
public ICommand SelectAllCommand { get { return ListVM.SelectAllCommand; } }
public bool? AreAllSelected
{
get
{
if (ListVM == null)
return false;
return ListVM.AreAllSelected;
}
}
private void OnListVmChanged(object sender, PropertyChangedEventArgs e)
{
if (e.PropertyName == "AreAllSelected")
OnPropertyChanged("AreAllSelected");
}
}
我没有显示SelectAllCommand或个人实施项目选择在这里，但它似乎并不相关。当用户在列表中选择一个项目（或单击问题复选框以选择/取消选择所有项目），我已经验证了OnPropertyChanged（AreAllSelected）的代码行执行，并在调试跟踪，可以看到PropertyChanged事件订阅并做防火预期。但AreAllSelected属性的get只执行一次 - 当视图实际呈现。 Visual Studio的输出窗口没有报告任何数据绑定错误，所以从我可以告诉，CheckBox的IsSelected属性正确绑定。
I'm not showing the implementation of SelectAllCommand or individual item selection here, but it doesn't seem to be relevant. When the user selects a single item in the list (or clicks the problem CheckBox to select/de-select all items), I have verified that the OnPropertyChanged("AreAllSelected") line of code executes, and tracing in the debugger, can see the PropertyChanged event is subscribed to and does fire as expected. But the AreAllSelected property's get is only executed once - when the view is actually rendered. Visual Studio's Output window does not report any data binding errors, so from what I can tell, the CheckBox's IsSelected property is properly bound.
如果我用一个按钮代替复选框
If I replace the CheckBox with a Button:
<Button Content="{Binding SelectAllText}" Command="{Binding SelectAllCommand}"/>
和更新VM：
...
public string SelectAllText
{
get
{
var msg = "Select All";
if (ListVM != null && ListVM.AreAllSelected != null && ListVM.AreAllSelected.Value)
msg = "Deselect All";
return msg;
}
}
...
private void OnListVmChanged(object sender, PropertyChangedEventArgs e)
{
if (e.PropertyName == "AreAllSelected")
OnPropertyChanged("SelectAllText");
}
一切正常 - 因为被选中的所有项目按钮的文本被更新/ desected。是否有什么我失踪有关CheckBox的IsSelected属性绑定？
everything works as expected - the button's text is updated as all items are selected/desected. Is there something I'm missing about the Binding on the CheckBox's IsSelected property?
感谢您的帮助！
推荐答案
我发现这个问题。似乎在WPF 3.0存在一个错误对器isChecked单向绑定引起的结合被除去。由于这个帖子的协助，这听起来像错误是固定在WPF 4.0
I found the problem. It seems a bug existed in WPF 3.0 with OneWay bindings on IsChecked causing the binding to be removed. Thanks to this post for the assistance, it sounds like the bug was fixed in WPF 4.0
要复制，创建一个新的WPF项目。
To reproduce, create a new WPF project.
添加FooViewModel的.cs：
Add a FooViewModel.cs:
using System;
using System.ComponentModel;
using System.Windows.Input;
namespace Foo
{
public class FooViewModel : INotifyPropertyChanged
{
private bool? _isCheckedState = true;
public FooViewModel()
{
ChangeStateCommand = new MyCmd(ChangeState);
}
public bool? IsCheckedState
{
get { return _isCheckedState; }
}
public ICommand ChangeStateCommand { get; private set; }
private void ChangeState()
{
switch (_isCheckedState)
{
case null:
_isCheckedState = true;
break;
default:
_isCheckedState = null;
break;
}
OnPropertyChanged("IsCheckedState");
}
public event PropertyChangedEventHandler PropertyChanged;
protected void OnPropertyChanged(string propertyName)
{
var changed = PropertyChanged;
if (changed != null)
changed(this, new PropertyChangedEventArgs(propertyName));
}
}
public class MyCmd : ICommand
{
private readonly Action _execute;
public event EventHandler CanExecuteChanged;
public MyCmd(Action execute)
{
_execute = execute;
}
public void Execute(object parameter)
{
_execute();
}
public bool CanExecute(object parameter)
{
return true;
}
}
}
修改Window1.xaml.cs
Modify Window1.xaml.cs:
using System.Windows;
using System.Windows.Controls.Primitives;
namespace Foo
{
public partial class Window1
{
public Window1()
{
InitializeComponent();
}
private void OnClick(object sender, RoutedEventArgs e)
{
var bindingExpression = MyCheckBox.GetBindingExpression(ToggleButton.IsCheckedProperty);
if (bindingExpression == null)
MessageBox.Show("IsChecked property is not bound!");
}
}
}
修改Window1.xaml：
Modify Window1.xaml:
<Window
x:Class="Foo.Window1"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:vm="clr-namespace:Foo"
Title="Window1"
Height="200"
Width="200"
>
<Window.DataContext>
<vm:FooViewModel />
</Window.DataContext>
<StackPanel>
<CheckBox
x:Name="MyCheckBox"
Command="{Binding ChangeStateCommand}"
IsChecked="{Binding Path=IsCheckedState, Mode=OneWay}"
Content="Foo"
IsThreeState="True"
Click="OnClick"/>
<Button Command="{Binding ChangeStateCommand}" Click="OnClick" Content="Change State"/>
</StackPanel>
</Window>
点击该按钮几次，看到真实，空（不是假的）之间的CheckBox的状态切换。但点击复选框，你会看到，绑定是从器isChecked属性中删除
Click on the button a few times and see the CheckBox's state toggle between true and null (not false). But click on the CheckBox and you will see that the Binding is removed from the IsChecked property.
解决方法：
更新器isChecked结合是双向并设置其UpdateSourceTrigger是明确的：
Update the IsChecked binding to be TwoWay and set its UpdateSourceTrigger to be explicit:
IsChecked="{Binding Path=IsCheckedState, Mode=TwoWay, UpdateSourceTrigger=Explicit}"
和更新绑定属性所以它不再是只读的：
and update the bound property so it's no longer read-only:
public bool? IsCheckedState
{
get { return _isCheckedState; }
set { }
}
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