C# 按此键添加图像

我试图在按下键盘按钮时将图像添加到画布：

public MainWindow()
{
  InitializeComponent();
}

public void OnKeyDownHandler(object sender, KeyEventArgs e)
{
    Image img = new Image();
        img.Source = new BitmapImage(new Uri("C:\\Users\\Public\\Pictures\\Sample Pictures\\Koala.jpg"));

        Canvas.SetTop(img, 0);
        Canvas.SetLeft(img, 0);
        this.Content = img;
}

以下是XAML：

<Canvas KeyDown="OnKeyDownHandler" HorizontalAlignment="Left" Height="166" Margin="118,89,0,0" VerticalAlignment="Top" Width="300"/>

---

但当我按下一个键时，什么也没发生。如果我在MainWindow方法中输入相同的代码，它将加载图片。我错在哪里？

我认为你应该增加体重+身高，并将图像添加到画布上。孩子们

img.Width = value;
img.Height = value;
MyCanvas.Children.Add(img);

---

你需要给你的画布起一个名字，让画布可以聚焦，然后在构造器中关注它。下面是代码片段

<Canvas KeyDown="OnKeyDownHandler" Focusable="True" HorizontalAlignment="Left" Height="166" Margin="118,89,0,0" VerticalAlignment="Top" Width="300" Name="myCanvas"/>

代码隐藏：

    public MainWindow()
    {
        InitializeComponent();
        myCanvas.Focus(); //<-- Do this First

    }



    private void OnKeyDownHandler(object sender, KeyEventArgs e)
    {
        Image img = new Image();
        img.Source = new BitmapImage(new Uri("C:\\Users\\Public\\Pictures\\Sample Pictures\\Koala.jpg"));

        Canvas.SetTop(img, 0);
        Canvas.SetLeft(img, 0);
        this.Content = img;
    }

public主窗口（）
{
初始化组件（）；
myCanvas.Focus（）；//有几点：

在XAML中，您必须为画布指定一个名称，以便您可以从代码中将其关联起来。然后您可以使用
maincavas.Children.Add（img）；
当您使用单词
this
时，您指的是类的实例—您的窗口，而不是画布。
this.Content=
与编写
Content=
相同，并且会将img放在窗口上。这将直接在构造函数中发生
最后一点是焦点：xaml中定义的画布未获得焦点，并且未激发事件。如果向画布添加背景，则可以激发
maincavas\u MouseDown
。即使有背景，也不会激发
KeyDown
在画布上设置焦点并在xaml中添加
Focusable=“True”
后，“keyDown”也将启动（其他人已经回答过）
xaml：

在OnKeyDownHandler中放置断点，并确定是否触发事件。我想这不是因为画布未聚焦。我已编辑了您的标题。请参阅“”，其中一致意见是“不，他们不应该”。
<Canvas Name="MainCanvas" Focusable="True" Background="AliceBlue" HorizontalAlignment="Left" Height="160" Margin="68,39,0,0" VerticalAlignment="Top" Width="192" KeyDown="MainCanvas_KeyDown" MouseDown="MainCanvas_MouseDown_1" >

public partial class MainWindow : Window
{
    Image img = new Image { Source = new BitmapImage(new Uri("C:\\Users\\Public\\Pictures\\Koala.jpg")) };
    public MainWindow()
    {
        InitializeComponent();
        MainCanvas.Focus();
        //this.Content = img; 
        //Content = img; //same as the above. you don't need to write "this".
    }

    private void button_Click(object sender, RoutedEventArgs e)
    {// will work even if canvas has no background
        MainCanvas.Children.Add(img);
    }

    private void MainCanvas_KeyDown(object sender, KeyEventArgs e)
    {
        //event will not fire. Canvas does not get the focus
        //if you must have KeyDown trigger the event, you need MainCanvas.Focus() in the constructor, and Focusable="True" in the XAML.
        MainCanvas.Children.Add(img);
    }

    private void MainCanvas_MouseDown_1(object sender, MouseButtonEventArgs e)
    {
        //This event will only fire if the canvas can get the focus: e.g. if it has some background.
        MainCanvas.Children.Add(img); //canvas control has the name MainCanvas inside the xaml
        //the below will work, but place the image on the window, because "this" means the class instance, not the method or event you are in.
        //this.Content = img;
    }
}