Question

我的控件中有一个依赖项属性，该属性将OneWayToSource绑定到视图模型。我不知道如何用一个非静态值初始化它。如果我尝试在控件的构造函数中对其进行初始化，则属性值将更改为所需的值，但是由于某种原因会立即将其更改回原值。考虑以下代码：

ButterflyControl.xaml.cs

using System;
using System.Diagnostics;
using System.Windows;

namespace OneWayToSourceTest
{
    public partial class ButterflyControl
    {

        public ButterflyControl()
        {
            InitializeComponent();
            RefreshAction = Refresh;
        }

        public static readonly DependencyProperty RefreshActionProperty = DependencyProperty.Register(
            name: nameof(RefreshAction),
            propertyType: typeof(Action),
            ownerType: typeof(ButterflyControl),
            typeMetadata: new PropertyMetadata(null, RefreshActionPropertyChanged));

        public Action RefreshAction
        {
            get => (Action)GetValue(RefreshActionProperty);
            set => SetValue(RefreshActionProperty, value);
        }

        private static void RefreshActionPropertyChanged(DependencyObject sender, DependencyPropertyChangedEventArgs e)
        {
            // For debugging purposes, observe changed to the RefreshAction property.
            Debug.WriteLine("RefreshAction changed from '{0}' to '{1}'", (e.OldValue as Action)?.Method.Name, (e.NewValue as Action)?.Method.Name);
        }

        private void Refresh()
        {
            // Refresh code goes here.
        }

    }
}

ButterflyControl.xaml

<UserControl x:Class="OneWayToSourceTest.ButterflyControl"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
             mc:Ignorable="d" 
             d:DesignHeight="450" d:DesignWidth="800" >

    <Grid />

</UserControl>

MainWindow.xaml

<Window x:Class="OneWayToSourceTest.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:oneWayToSourceTest="clr-namespace:OneWayToSourceTest"
        mc:Ignorable="d"
        Title="MainWindow" Height="450" Width="800">

    <oneWayToSourceTest:ButterflyControl RefreshAction="{Binding RefreshAction, Mode=OneWayToSource}" />

</Window>

Startup.cs

using System;

namespace OneWayToSourceTest
{
    public static class Startup
    {

        [STAThread]
        public static void Main()
        {
            MainWindow window = new MainWindow();
        }

    }
}

运行该程序时，输出窗口显示：

RefreshAction从''更改为``Refresh''
RefreshAction从``Refresh''更改为``

我在某个地方犯了一个错误，还是我采取了错误的方法？如果我采用了错误的方法，用非静态值初始化OneWayToSource依赖项属性的合适方法是什么？

Answer 1

将初始化移至Loaded事件处理程序，该事件处理程序在建立绑定之后调用。

public ButterflyControl()
{
    InitializeComponent();

    Loaded += (s, e) => RefreshAction = Refresh;
}

有关更多信息，请参见Object Lifetime Events。

如何初始化OneWayToSource依赖项属性？

1 个答案: