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Canvas 画矩形：
view和viewModel 绑定一起才显示移动轨迹（可以定义一个string  看是否绑定属性的路径是正确的）
前台（绑定事件和显示移动的线）：

<Canvas Name="canvas" Background="#01FFFFFF" PreviewMouseLeftButtonDown="VDM_MouseLeftButtonDown" PreviewMouseMove="VDM_MouseMove"PreviewMouseLeftButtonUp="VDM_MouseLeftButtonUp">
</Canvas><Canvas><Rectangle IsHitTestVisible="False" Stroke="Red" x:Name="rect"StrokeDashArray="1,2" StrokeThickness="1" Stretch="Fill" Width="{Binding RectWidth}" Height="{Binding RectHeight}" Canvas.Left="{Binding RectLeft}" Canvas.Top="{Binding RectTop}"/>
</Canvas>

后台：

若view和其他viewmodel绑定了 可以用（rect.DataContext = Model;  DVMModel Model = new DVMModel();  DVMModel属性定义）
如果view和后台绑定：

bool is_LeftButtonDown = false;public void VDM_MouseLeftButtonDown(object view, MouseButtonEventArgs e)
{Canvas canvas = view as Canvas;Point pt = Mouse.GetPosition(canvas);downPt = pt;is_LeftButtonDown = true;if (pt.X < 0 || pt.X > canvas.ActualWidth || pt.Y < 0 || pt.Y > canvas.ActualHeight){is_LeftButtonDown = false;}
}

鼠标移动绘制矩形

public void VDM_MouseMove(object view, MouseEventArgs e)
{//鼠标坐标点Point pt = Mouse.GetPosition(view as Canvas);if (is_LeftButtonDown && e.LeftButton == MouseButtonState.Pressed)	//确定鼠标左键处于按下状态{isMove = true;if (pt.X < 0 || pt.X > canvas.ActualWidth || pt.Y < 0 || pt.Y > canvas.ActualHeight){is_LeftButtonDown = false;Model.RectHeight = 0;Model.RectWidth = 0;}else{double left = (downPt.X < pt.X) ? downPt.X : pt.X;double top = (downPt.Y < pt.Y) ? downPt.Y : pt.Y;double width = Math.Abs(downPt.X - pt.X);double height = Math.Abs(downPt.Y - pt.Y);// 画矩形Model.RectLeft = left;Model.RectTop = top;Model.RectWidth = width;Model.RectHeight = height;canvas.CaptureMouse();	//捕获鼠标}}
}

鼠标弹起完成矩形绘制

public void VDM_MouseLeftButtonUp(object view, MouseButtonEventArgs e)
{Canvas canvas = view as Canvas;if (is_LeftButtonDown && isMove){is_LeftButtonDown = false;isMove = false;Point pt = Mouse.GetPosition(canvas);double Wscale = canvas.ActualWidth / SingalSize.Width;		//SingalSize 分辨率double Hscale = canvas.ActualHeight / SingalSize.Height;double left = (downPt.X < pt.X) ? downPt.X : pt.X;double top = (downPt.Y < pt.Y) ? downPt.Y : pt.Y;double width = Math.Abs(pt.X - downPt.X);double height = Math.Abs(pt.Y - downPt.Y);OsdStartX.Text = Convert.ToInt32(left).ToString();OsdStartY.Text = Convert.ToInt32(top).ToString();if (width * Wscale > 512)HLength.Text = "512";elseHLength.Text = Convert.ToInt32(width * Wscale).ToString();if (height * Hscale > 64)VLength.Text = "64";elseVLength.Text = Convert.ToInt32(height * Hscale).ToString();// 画矩形Model.RectHeight = 0;Model.RectWidth = 0;canvas.ReleaseMouseCapture();	//释放捕获鼠标}
}