C#WPF屏幕截图应用程序--通过鼠标事件处理画布上的绘图

我正在用WPF制作一个截图程序。我不明白的是我应该如何使用鼠标点击事件。我的所有鼠标事件都是在代码隐藏中处理的，这非常有效，但我想将我的项目转换为MVVM风格。下面是我所有的ScreenshotTab代码，它是承载屏幕截图的usercontrol（它实际上被设计为放置在tabcontrol选项卡项中）：

公共部分类屏幕快照选项卡：用户控件
{
公共屏幕快照选项卡（）
{
初始化组件（）；
}
公共屏幕快照选项卡（位图图像屏幕快照，窗口）
{
初始化组件（）；
imgControl.Source=屏幕截图；
imgControl.MaxWidth=屏幕截图.Width；
imgControl.MaxHeight=屏幕截图.Height；
canvas.Height=screenshot.Height；
canvas.MinHeight=屏幕截图.Height；
canvas.MaxHeight=屏幕截图.Height；
canvas.Width=screenshot.Width；
canvas.MinWidth=屏幕截图.Width；
canvas.MaxWidth=屏幕截图.Width；
mainWindow=作为主窗口的窗口；
}
公共场所被保留
{
得到；
设置
}
公共位图图像截图
{
得到
{
if（imgControl.Source为位图图像）
{
将imgControl.Source作为BitmapImage返回；
}
其他的
{
返回null；
}
}
}
//在事件处理程序内部的逻辑流中按需要的顺序列出。
私有主窗口主窗口；
私人椭圆圈；
私有多段线；
专用点起始点；
专用点端点；
专线；
私有矩形；
私人点左上角；
//我可能不需要一本书。
私有布尔图；
私有无效imgControl_MouseDown（对象发送器，MouseButtonEventArgs e）
{
//Show（“鼠标按下事件正在工作…”）；
//MessageBox.Show（“mainwindow.toolselected=“+mainwindow.toolselected.ToString（））；
//设置直线的起点，该起点不变
//当用户移动鼠标时。
//启用表示启用时正在绘制的标志。
isDrawing=true；
开关（主窗口。选择工具）
{                    
case DrawingTool.FreeDraw：
多段线=新的多段线（）；
设置行程特性（多段线）；
polyLine.Points.Add（例如GetPosition（canvas））；
canvas.Children.Add（多段线）；
打破
案例绘图工具线：
行=新行（）；
设定行程特性（直线）；
line.X1=e.GetPosition（画布）.X；
line.Y1=e.GetPosition（画布）.Y；
line.X2=e.GetPosition（画布）.X；
line.Y2=e.GetPosition（画布）.Y；
canvas.Children.Add（行）；
打破
案例绘图工具矩形：
矩形=新矩形（）；
设置行程属性（矩形）；
startPoint=e.GetPosition（此）；
端点=e.GetPosition（此）；
SetLeft（矩形，startPoint.X）；
SetTop（矩形，startPoint.X）；
canvas.Children.Add（矩形）；
打破
案例绘图工具圆：
圆=新椭圆（）；
设定行程特性（圆形）；
startPoint=e.GetPosition（此）；
端点=e.GetPosition（此）；
Canvas.SetLeft（圆形，startPoint.X）；
Canvas.SetTop（圆形，startPoint.X）；
canvas.Children.Add（圆圈）；
打破
机箱绘图工具橡皮擦：
打破
违约：
打破
}
}
私有void SetStrokeProperties（形状）
{
shape.Stroke=新的SolidColorBrush（mainWindow.color）；
shape.StrokeThickness=3；
}
//这是我们的橡皮擦活动。
//选择工具时，它只是从对象中删除元素
//是橡皮擦工具，我们把鼠标放下了。
MouseOver上的私有void（对象发送方，MouseEventArgs e）
{
//MessageBox.Show（“耶，鼠标悬停在名为…”的事件上）；
if（isDrawing&（mainWindow.toolSelected==DrawingTool.橡皮擦））
{
canvas.Children.Remove（发送方作为UIElement）；
}
}
私有无效imgControl\u MouseMove（对象发送方，MouseEventArgs e）
{
if（isDrawing）
{
开关（主窗口。选择工具）
{
case DrawingTool.FreeDraw：
polyLine.Points.Add（例如GetPosition（canvas））；
打破
案例绘图工具线：
line.X2=e.GetPosition（画布）.X；
line.Y2=e.GetPosition（画布）.Y；
打破
案例绘图工具矩形：
端点=e.GetPosition（此）；
矩形.Width=Math.Abs（endPoint.X-startPoint.X）；
rectangle.Height=Math.Abs（endPoint.Y-startPoint.Y）；
//向下向右。
if（（endPoint.X>=startPoint.X）和&（endPoint.Y>=startPoint.Y））
{
//在这种情况下，起点是矩形的左上角点。
左上角.X=起始点.X；
左上角.Y=起始点.Y；
SetLeft（矩形，左上角.X）；
画布.SetTop（矩形，左上角.Y）；
}
//向上向右。
如果（（endPoint.X>=startPoint.X）&&&（endPoint.Y=startPoint.X）&&（endPoint.Y我用一个c
public partial class ScreenshotTab : UserControl
{
    public ScreenshotTab()
    {
        InitializeComponent();
    }

    public ScreenshotTab(BitmapImage screenshot, Window window)
    {
        InitializeComponent();
        imgControl.Source = screenshot;
        imgControl.MaxWidth = screenshot.Width;
        imgControl.MaxHeight = screenshot.Height;
        canvas.Height = screenshot.Height;
        canvas.MinHeight = screenshot.Height;
        canvas.MaxHeight = screenshot.Height;
        canvas.Width = screenshot.Width;
        canvas.MinWidth = screenshot.Width;
        canvas.MaxWidth = screenshot.Width;
        mainWindow = window as MainWindow;
    }

    public bool isSaved
    {
        get;
        set;
    }


    public BitmapImage Screenshot
    {
        get
        {
            if (imgControl.Source is BitmapImage)
            {
                return imgControl.Source as BitmapImage;
            }
            else
            {
                return null;
            }
        }
    }

    // Listed in the order they are needed in the logic flow inside the event handlers.
    private MainWindow mainWindow;
    private Ellipse circle;
    private Polyline polyLine;
    private Point startPoint;
    private Point endPoint;
    private Line line;
    private Rectangle rectangle;
    private Point topLeft;
    // I probably don't need a bool.
    private bool isDrawing;



    private void imgControl_MouseDown(object sender, MouseButtonEventArgs e)
    {
        // MessageBox.Show("Mouse down event is working...");
        // MessageBox.Show("mainwindow.toolselected = " + mainWindow.toolSelected.ToString());
        // Sets the starting point of the line, which doesn't change
        // as the user moves their mouse.

        // Turns on a flag that represents that we are drawing when on.
        isDrawing = true;

        switch (mainWindow.toolSelected)
        {                    
            case DrawingTool.FreeDraw:
                polyLine = new Polyline();
                SetStrokeProperties(polyLine);
                polyLine.Points.Add(e.GetPosition(canvas));
                canvas.Children.Add(polyLine);
                break;
            case DrawingTool.Line:
                line = new Line();
                SetStrokeProperties(line);
                line.X1 = e.GetPosition(canvas).X;
                line.Y1 = e.GetPosition(canvas).Y;
                line.X2 = e.GetPosition(canvas).X;
                line.Y2 = e.GetPosition(canvas).Y;
                canvas.Children.Add(line);
                break;
            case DrawingTool.Rectangle:
                rectangle = new Rectangle();
                SetStrokeProperties(rectangle);
                startPoint = e.GetPosition(this);
                endPoint = e.GetPosition(this);
                Canvas.SetLeft(rectangle, startPoint.X);
                Canvas.SetTop(rectangle, startPoint.X);
                canvas.Children.Add(rectangle);
                break;
            case DrawingTool.Circle:
                circle = new Ellipse();
                SetStrokeProperties(circle);
                startPoint = e.GetPosition(this);
                endPoint = e.GetPosition(this);
                Canvas.SetLeft(circle, startPoint.X);
                Canvas.SetTop(circle, startPoint.X);
                canvas.Children.Add(circle);
                break;
            case DrawingTool.Eraser:

                break;
            default:
                break;
        }
    }

    private void SetStrokeProperties(Shape shape)
    {
        shape.Stroke = new SolidColorBrush(mainWindow.color);
        shape.StrokeThickness = 3;
    }

    // This is our eraser event.
    // It simply removes the element from the object when the tool selected
    // is the eraser tool and we have the mouse down.
    private void OnMouseOver(object sender, MouseEventArgs e)
    {
        // MessageBox.Show("Yay, mouse over event called...");
        if (isDrawing && (mainWindow.toolSelected == DrawingTool.Eraser))
        {
            canvas.Children.Remove(sender as UIElement);
        }
    }

    private void imgControl_MouseMove(object sender, MouseEventArgs e)
    {
        if (isDrawing)
        {
            switch (mainWindow.toolSelected)
            {
                case DrawingTool.FreeDraw:
                    polyLine.Points.Add(e.GetPosition(canvas));
                    break;
                case DrawingTool.Line:
                    line.X2 = e.GetPosition(canvas).X;
                    line.Y2 = e.GetPosition(canvas).Y;
                    break;
                case DrawingTool.Rectangle:
                    endPoint = e.GetPosition(this);
                    rectangle.Width = Math.Abs(endPoint.X - startPoint.X);
                    rectangle.Height = Math.Abs(endPoint.Y - startPoint.Y);
                    // down and to the right.
                    if ((endPoint.X >= startPoint.X) && (endPoint.Y >= startPoint.Y))
                    {
                        // In this case, the start point is the top left point of the rectangle.
                        topLeft.X = startPoint.X;
                        topLeft.Y = startPoint.Y;
                        Canvas.SetLeft(rectangle, topLeft.X);
                        Canvas.SetTop(rectangle, topLeft.Y);
                    }
                    // up and to the right.
                    else if ((endPoint.X >= startPoint.X) && (endPoint.Y <= startPoint.Y))
                    {
                        topLeft.X = endPoint.X - rectangle.Width;
                        topLeft.Y = endPoint.Y;
                        Canvas.SetLeft(rectangle, topLeft.X);
                        Canvas.SetTop(rectangle, topLeft.Y);
                    }
                    // up and to the left...
                    else if ((endPoint.X <= startPoint.X) && (endPoint.Y <= startPoint.Y))
                    {
                        topLeft.X = endPoint.X;
                        topLeft.Y = endPoint.Y;
                        Canvas.SetLeft(rectangle, topLeft.X);
                        Canvas.SetTop(rectangle, topLeft.Y);
                    }
                    // down to the left...
                    else if ((endPoint.X <= startPoint.X) && (endPoint.Y >= startPoint.Y))
                    {
                        topLeft.X = startPoint.X - rectangle.Width;
                        topLeft.Y = endPoint.Y - rectangle.Height;
                        Canvas.SetLeft(rectangle, topLeft.X);
                        Canvas.SetTop(rectangle, topLeft.Y);
                    }
                    break;
                case DrawingTool.Circle:
                    endPoint = e.GetPosition(this);
                    circle.Width = Math.Abs(endPoint.X - startPoint.X);
                    circle.Height = Math.Abs(endPoint.Y - startPoint.Y);
                    // down and to the right.
                    if ((endPoint.X >= startPoint.X) && (endPoint.Y >= startPoint.Y))
                    {
                        // In this case, the start point is the top left point of the rectangle.
                        topLeft.X = startPoint.X;
                        topLeft.Y = startPoint.Y;
                        Canvas.SetLeft(circle, topLeft.X);
                        Canvas.SetTop(circle, topLeft.Y);
                    }
                    // up and to the right.
                    else if ((endPoint.X >= startPoint.X) && (endPoint.Y <= startPoint.Y))
                    {
                        topLeft.X = endPoint.X - circle.Width;
                        topLeft.Y = endPoint.Y;
                        Canvas.SetLeft(circle, topLeft.X);
                        Canvas.SetTop(circle, topLeft.Y);
                    }
                    // up and to the left...
                    else if ((endPoint.X <= startPoint.X) && (endPoint.Y <= startPoint.Y))
                    {
                        topLeft.X = endPoint.X;
                        topLeft.Y = endPoint.Y;
                        Canvas.SetLeft(circle, topLeft.X);
                        Canvas.SetTop(circle, topLeft.Y);
                    }
                    // down to the left...
                    else if ((endPoint.X <= startPoint.X) && (endPoint.Y >= startPoint.Y))
                    {
                        topLeft.X = startPoint.X - circle.Width;
                        topLeft.Y = endPoint.Y - circle.Height;
                        Canvas.SetLeft(circle, topLeft.X);
                        Canvas.SetTop(circle, topLeft.Y);
                    }
                    break;
                default:
                    break;
            }
        }
    }

    private void imgControl_MouseUp(object sender, MouseButtonEventArgs e)
    {
        isSaved = false;
        switch (mainWindow.toolSelected)
        {
            case (DrawingTool.FreeDraw):
                polyLine.MouseEnter += OnMouseOver;
                break;
            case (DrawingTool.Line):
                line.MouseEnter += OnMouseOver;
                break;
            case (DrawingTool.Rectangle):
                rectangle.MouseEnter += OnMouseOver;
                break;
            case (DrawingTool.Circle):
                circle.MouseEnter += OnMouseOver;
                break;
        }
        isDrawing = false;
        // MessageBox.Show("Mouse up event fired...");
    }
}

public interface IMouseArgs
{
    Point Pos { get; }
    void Capture();
    void Release();
    bool Handled { get; set; }
    ... lots of other stuff
}

<SomeControl>
    <i:Interaction.Triggers>
        <i:EventTrigger EventName="MouseDown">
            <cmd:EventToCommand Command="{Binding MouseDownCommand}"
                PassEventArgsToCommand="True"
                EventArgsConverter="{StaticResource ClickConverter}"
                EventArgsConverterParameter="{Binding RelativeSource={RelativeSource Mode=FindAncestor, AncestorType=local:SomeParentWindow}}"/>
        </i:EventTrigger>