Question

我是wpf的新手，我想做的是为xaml添加3个按钮和一个画布。每个按钮代表一种颜色。

黄色
绿色
黑色根据需要，只能有一个黄色，只有一个绿色和多个黑色点。将它们放下后保存黄色和绿色点的索引似乎是合理的，以便稍后可以通过索引删除它们，然后重新绘制它们。只要我只使用一种颜色（黄色或绿色点）一切正常，但当我按顺序应用按钮时：“A B C A B”或（A B A B）绿色会覆盖黑点。

所以我的问题是，我做错了什么？有比这更好的方法吗？获取画布索引是否有比使用canvas.Children.Count;更好的方法？

编辑：似乎使用索引有点乱，应该将它们存储在UIElement而不是

XAML

<StackPanel Background="Aqua">
    <Button Click="ButtonA_Click" Width="80">putDOT_A</Button>
    <Button Click="ButtonB_Click" Width="80">putDOT_B</Button>
    <Button Click="ButtonC_Click" Width="80">putDOT_C</Button>
    <Canvas 
            Name="canvas"
            Panel.ZIndex="0"
            Background="White"
            ClipToBounds="true"
            Width="400" Height="400" 
            MouseDown="Canvas_MouseDown" >
    </Canvas>
</StackPanel>

CS

 {
    public int indexA = -1;
    public int indexB = -1;
    public MainWindow()
    {
        InitializeComponent();
    }
    private void RemoveAxisPoint(int index)
    {
        if (index >= 0)
        {
            canvas.Children.RemoveAt(index - 1);
        }
    }
    private enum MyCurrentButton
    {
        Dot, A, B
    }
    private void Canvas_MouseDown(object sender, MouseButtonEventArgs e)
    {
        switch (curr)
        {
            case MyCurrentButton.A:
                PutA(e);
                break;
            case MyCurrentButton.B:
                PutB(e);
                break;
            case MyCurrentButton.Dot:
                PutDot(e);
                break;
            default:
                return;
        }
    }
    private void PutDot(MouseButtonEventArgs e)
    {
        Dot dot = new Dot(canvas);
        dot.Draw(e.GetPosition(canvas));
    }
    private void PutB(MouseButtonEventArgs e)
    {
        Dot dot = new Dot(canvas,0, 255, 0);
        RemoveAxisPoint(indexB);
        dot.DrawB(e.GetPosition(canvas));
        indexB = canvas.Children.Count;
    }
    private void PutA(MouseButtonEventArgs e)
    {
        Dot dot = new Dot(canvas, 255, 255, 0);
        RemoveAxisPoint(indexA);
        dot.DrawA(e.GetPosition(canvas));
        indexA = canvas.Children.Count;
    }
    private MyCurrentButton curr = MyCurrentButton.Dot;
    private void ButtonA_Click(object sender, RoutedEventArgs e)
    {
        curr = MyCurrentButton.A;
    }
    private void ButtonB_Click(object sender, RoutedEventArgs e)
    {
        curr = MyCurrentButton.B;
    }
    private void ButtonC_Click(object sender, RoutedEventArgs e)
    {
        curr = MyCurrentButton.Dot;
    }
    class Dot : IDraw
    {
        private readonly Canvas _canvas;
        public Ellipse dot { get; private set; }
        public double Width { get; set; }
        public double Height { get; set; }
        public Brush Fill { get; private set; }
        public Dot(Canvas canvas,  byte r = 0, byte g = 0, byte b = 0)
        {
            _canvas = canvas;
            SolidColorBrush color = new SolidColorBrush(Color.FromRgb(r, g, b));
            dot = new Ellipse
            {
                Width = 10,
                Height = 10,
                Fill = color
            };
        }
        public void DrawA(Point location)
        {
            Canvas.SetLeft(dot, location.X - (dot.Width / 2));
            Canvas.SetTop(dot, location.Y - (dot.Height / 2));
            _canvas.Children.Add(dot);
        }
        public void DrawB(Point location)
        {
            Canvas.SetLeft(dot, location.X - (dot.Width / 2));
            Canvas.SetTop(dot, location.Y - (dot.Height / 2));
            _canvas.Children.Add(dot);
        }
        public void Draw(Point location)
        {
            Canvas.SetLeft(dot, location.X - (dot.Width / 2));
            Canvas.SetTop(dot, location.Y - (dot.Height / 2));
            _canvas.Children.Add(dot);
        }
    }
    public interface IDraw
    {

        void Draw(Point location);
    }
}

Answer 1

您的代码不起作用的原因是，在删除第一个索引后，第二个索引（如果大于第一个索引）是错误的。

所以要解决这个问题......

 RemoveAxisPoint(indexA);
 if(indexB > indexA)indexB--;

和...

 RemoveAxisPoint(indexB);
 if(indexA > indexB)indexA--;

所以这将解决当前的问题。但是你的设计非常脆弱，一旦你改变它就会再次破裂。我建议使用Canvas.Children.Remove（）而不是RemoveAt（），这会略微降低性能，但会大大提高健壮性。

如何获取最后一个canvas元素索引wpf

1 个答案: