C#WPF:View无法获取属性的更改

Question

我正在学习关于属性绑定的wpf c#.我创建了一个简单的wpf应用程序.我尝试将矩形控件的宽度绑定到后面的代码中的属性"PageWidth".但不知何故它不起作用(视图不会得到属性的更改).我想要实现的目标: - 矩形的宽度在代码后面用100初始化 - 如果点击按钮"width ++",矩形的宽度逐步增加10.我的代码中是否遗漏了一些东西？请建议并随时修改我的代码.提前致谢.

XAML:

<Window x:Class="MyWpfApp.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">
<Grid>
    <Rectangle
        Fill="#FF6262BD"
        HorizontalAlignment="Left"
        Margin="23,24,0,0"
        Stroke="Black"
        VerticalAlignment="Top"
        Width="{Binding Path=PageWidth}"
        Height="100" />
    <Button
        Content="Width++"
        HorizontalAlignment="Left"
        Margin="35,129,0,0"
        VerticalAlignment="Top"
        Width="75"
        Click="Button_Click" />

</Grid>

xaml.cs:

using System;
using System.Windows;

namespace MyWpfApp
{
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
            PageWidth = 100;
        }

        private Int32 _pageWidth;
        public Int32 PageWidth
        {
            get
            {
                return _pageWidth;
            }
            set
            { 
                if ( _pageWidth != value )
                {
                     _pageWidth = value;
                }
            }
         }

         private void Button_Click(object sender, RoutedEventArgs e)
         {
             if ( PageWidth <= 200 )
             {
                  PageWidth += 10;
             }
         }
     }
 }

Answer 1

您的代码中存在两个问题:

• 你没有设置DataContext,所以绑定没有引用(它不知道它应该从哪个对象获取PageWidth属性)
• PageWidth不是依赖项属性,也不会引发PropertyChanged事件,因此在值更改时无法通知绑定系统.

要解决这些问题,您应该:

• 将DataContext设置为窗口本身:

  // in the constructor
  DataContext = this;
  

• 使MainWindow类实现INotifyPropertyChanged接口,并更改PageWidth属性以便它引发PropertyChanged事件:

  public partial class MainWindow : Window, INotifyPropertyChanged
  {
      ...
  
      public event PropertyChangedEventHandler PropertyChanged;
  
      protected virtual void OnPropertyChanged(string propertyName)
      {
          var handler = PropertyChanged;
          if (handler != null)
              handler(this, new PropertyChangedEventArgs(propertyName));
      }
  
      private Int32 _pageWidth;
      public Int32 PageWidth
      {
          get
          {
              return _pageWidth;
          }
          set
          { 
              if ( _pageWidth != value )
              {
                   _pageWidth = value;
                   OnPropertyChanged("PageWidth");
              }
          }
       }
  
       ...