Question

我在按键盘按钮时尝试将图像添加到画布：

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;
}

这是XAML：

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

但是当我按下按键时没有任何反应。如果我在MainWindow方法中放入相同的代码，它会加载图片。我哪里错了？

Answer 1

您需要为画布指定一个名称并使画布具有焦点，然后在构造函数中关注它。这是代码段

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

代码背后：

    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;
    }

Answer 2

有几点：

在您的XAML中，您必须为画布指定一个名称，以便您可以从代码中与它相关联。然后，您可以使用MainCanvas.Children.Add(img);
当你使用单词this时，你会引用类的实例 - 你的窗口，而不是画布。 this.Content=与编写Content=相同，并将img放在窗口上。这将直接在构造函数
最后一点是焦点：xaml中定义的画布没有得到焦点而且你的事件没有被触发。如果您向画布添加背景，则可以触发MainCanvas_MouseDown。即使有背景，也不会触发KeyDown。
将焦点设置在画布上并在xaml中添加Focusable="True"，＆＃39; keyDown＆＃39;也将开火（已经被其他人回答）

XAML：

<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" >

代码：

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;
    }
}

Answer 3

我认为您应该添加重量+高度并将图像添加到Canvas.Children

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

在按下的键上添加图像

3 个答案: