在WPF中使用MVVM拖动鼠标时绘制矩形

Question

下面是我的xaml.我在画布里面有一个图像.我想在图像上拖动鼠标时在图像上绘制矩形.我在WPF中成功完成了它.但现在我想在MVVM中做到这一点.我没有在代码中使用事件处理程序,而是希望将它们放在我的ViewModel中.我正在使用MVVM Foundation来实现MVVM.以下是MVVM Foundation的链接.http://mvvmfoundation.codeplex.com/

任何帮助都非常感谢.

XAML

<Canvas Name="cnvImage">
        <Image Height="348" HorizontalAlignment="Left" Margin="12,39,0,0" Name="imgPreview" 
               Stretch="Fill" VerticalAlignment="Top" Width="443" 
               Source="/Images/CapturedImage.png" 
                MouseDown="imgCamera_MouseDown" MouseMove="imgCamera_MouseMove" MouseUp="imgCamera_MouseUp" />
    </Canvas>

用代码写的代码

// This is the rectangle to be shown when mouse is dragged on camera image.
private Point startPoint;
private Rectangle rectSelectArea;


/// <summary>
/// 
/// </summary>
/// <param name="sender"></param>
/// <param name="e"></param>
private void imgCamera_MouseDown(object sender, MouseButtonEventArgs e)
{
    startPoint = e.GetPosition(cnvImage);

    // Remove the drawn rectanglke if any.
    // At a time only one rectangle should be there
    if (rectSelectArea != null)
        cnvImage.Children.Remove(rectSelectArea);

    // Initialize the rectangle.
    // Set border color and width
    rectSelectArea = new Rectangle
    {
        Stroke = Brushes.LightBlue,
        StrokeThickness = 2
    };

    Canvas.SetLeft(rectSelectArea, startPoint.X);
    Canvas.SetTop(rectSelectArea, startPoint.X);
    cnvImage.Children.Add(rectSelectArea);
}

/// <summary>
/// 
/// </summary>
/// <param name="sender"></param>
/// <param name="e"></param>
private void imgCamera_MouseMove(object sender, MouseEventArgs e)
{
    if (e.LeftButton == MouseButtonState.Released || rectSelectArea == null)
        return;

    var pos = e.GetPosition(cnvImage);

    // Set the position of rectangle
    var x = Math.Min(pos.X, startPoint.X);
    var y = Math.Min(pos.Y, startPoint.Y);

    // Set the dimenssion of the rectangle
    var w = Math.Max(pos.X, startPoint.X) - x;
    var h = Math.Max(pos.Y, startPoint.Y) - y;

    rectSelectArea.Width = w;
    rectSelectArea.Height = h;

    Canvas.SetLeft(rectSelectArea, x);
    Canvas.SetTop(rectSelectArea, y);
}

/// <summary>
/// 
/// </summary>
/// <param name="sender"></param>
/// <param name="e"></param>
private void imgCamera_MouseUp(object sender, MouseButtonEventArgs e)
{
    rectSelectArea = null;
}

我需要知道在viewmodel中需要写什么,因此需要在XAML中进行哪些更改.

提前致谢.

Answer 1

在这篇文章/项目中可以找到一种非常巧妙的实现调整大小的方法。如果您使用在那里实现的 DesignerItemStyle，您可以添加绑定支持，如下所示：

<Rectangle Style="{StaticResource DesignerItemStyle}"
           Canvas.Left="{Binding Path=Leftoffset, Mode=TwoWay}"
           Canvas.Top="{Binding Path=Topoffset, Mode=TwoWay}"
           Width="{Binding Path=Width, Mode=TwoWay}"
           Height="{Binding Path=Height, Mode=TwoWay}">    

这样就可以通过拖动来调整纯 XAML 中的内容大小，并使用标准 WPF 方法将值获取到底层 ViewModel。