WPF CommandParameter 绑定未更新

发布于 2024-09-06 10:11:16 字数 1733 浏览 1 评论 0原文

我正在尝试在 WPF 应用程序中使用 Command 和 CommandParameter 与按钮绑定。我有这个完全相同的代码在 Silverlight 中工作得很好，所以我想知道我做错了什么！

我有一个组合框和一个按钮，其中命令参数绑定到组合框 SelectedItem：

<Window x:Class="WPFCommandBindingProblem.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="MainWindow" Height="350" Width="525">
    <StackPanel Orientation="Horizontal">
        <ComboBox x:Name="combo" VerticalAlignment="Top" />
        <Button Content="Do Something" Command="{Binding Path=TestCommand}"
                CommandParameter="{Binding Path=SelectedItem, ElementName=combo}"
                VerticalAlignment="Top"/>        
    </StackPanel>
</Window>

背后的代码如下：

public partial class MainWindow : Window
{
    public MainWindow()
    {
        InitializeComponent();

        combo.ItemsSource = new List<string>(){
            "One", "Two", "Three", "Four", "Five"
        };

        this.DataContext = this;

    }

    public TestCommand TestCommand
    {
        get
        {
            return new TestCommand();
        }
    }

}

public class TestCommand : ICommand
{
    public bool CanExecute(object parameter)
    {
        return parameter is string && (string)parameter != "Two";
    }

    public void Execute(object parameter)
    {
        MessageBox.Show(parameter as string);
    }

    public event EventHandler CanExecuteChanged;

}

在我的 Silverlight 应用程序中，当组合框的 SelectedItem 更改时，CommandParameter 绑定会导致我的命令使用 CanExecute 方法将使用当前选定的项目重新评估，并且按钮启用状态也会相应更新。

对于 WPF，由于某种原因，仅当解析 XAML 并创建绑定时才会调用 CanExecute 方法。

有什么想法吗？

原文

I am trying to use Command and CommandParameter binding with Buttons in a WPF application. I have this exact same code working just fine in Silverlight so I am wondering what I have done wrong!

I have a combo box and a button, where the command parameter is bound to the combobox SelectedItem:

<Window x:Class="WPFCommandBindingProblem.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="MainWindow" Height="350" Width="525">
    <StackPanel Orientation="Horizontal">
        <ComboBox x:Name="combo" VerticalAlignment="Top" />
        <Button Content="Do Something" Command="{Binding Path=TestCommand}"
                CommandParameter="{Binding Path=SelectedItem, ElementName=combo}"
                VerticalAlignment="Top"/>        
    </StackPanel>
</Window>

The code behind is as follows:

public partial class MainWindow : Window
{
    public MainWindow()
    {
        InitializeComponent();

        combo.ItemsSource = new List<string>(){
            "One", "Two", "Three", "Four", "Five"
        };

        this.DataContext = this;

    }

    public TestCommand TestCommand
    {
        get
        {
            return new TestCommand();
        }
    }

}

public class TestCommand : ICommand
{
    public bool CanExecute(object parameter)
    {
        return parameter is string && (string)parameter != "Two";
    }

    public void Execute(object parameter)
    {
        MessageBox.Show(parameter as string);
    }

    public event EventHandler CanExecuteChanged;

}

With my Silverlight application, as the SelectedItem of the combobox changes, the CommandParameter binding causes the CanExecute method for my command to be re-evaluated with the currently selected item and the button enabled state is updated accordingly.

With WPF, for some reason, the CanExecute method is only invoked when the binding is created when the XAML is parsed.

Any ideas?

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趁年轻赶紧闹 2024-09-13 10:11:16

您需要告诉 WPF CanExecute 可以更改 - 您可以在 TestCommand 类中自动执行此操作，如下所示：

public event EventHandler CanExecuteChanged
{
    add{CommandManager.RequerySuggested += value;}
    remove{CommandManager.RequerySuggested -= value;}
}

每次视图中的属性发生更改时，WPF 都会询问 CanExecute。

You need to tell WPF that CanExecute can change - you can do this automatically in your TestCommand class like this:

public event EventHandler CanExecuteChanged
{
    add{CommandManager.RequerySuggested += value;}
    remove{CommandManager.RequerySuggested -= value;}
}

WPF will then ask CanExecute everytime a property changes in the view.

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