CustomControl计算自己的宽度和高度- ArrangeOverride被调用与bounds.Height=0.

Question

我正在尝试实现一个" playingcard"作为ContentView，它按比例计算其宽度和高度。ContentView的内容是一个带有一些标签的网格。当计算扑克牌控件的大小时，我需要告诉子/网格它可以占用多大的大小。在我第一次尝试使用MeasureOverride和ArrangeOverride时，它看起来像我所有的尝试在设置大小时被忽略。我简化了整个代码，只设置控件的最小大小，但大小仍然被忽略。

值得注意的是，ArrangeOverride(Rect bounds)被调用的参数值为bounds = { X=0, Y=0, Width=1013, Height=0 } 。为什么高度是0?我甚至宣布OnMeasure的最低高度为85，并且有足够的空间可用。我哪里做错了?

后面的自定义控件代码:

    public partial class CardView : ContentView
    {
        private const double minWidth = 55;
        private const double minHeight = 85;
        public CardView()
        {
            InitializeComponent();
            BackgroundColor = Colors.BlueViolet;
        }
        protected override Size MeasureOverride(double widthConstraint, double heightConstraint)
        {
            //define minimum size of control
            var minSize = new Size(minWidth, minHeight);
            System.Diagnostics.Debug.WriteLine($"MeasureOverride width={minSize.Width},height={minSize.Height}");
            return minSize;
        }
        protected override Size ArrangeOverride(Rect bounds) //bounds = { X=0, Y=0, Width=1013, Height=0 } 
        {
            Rect rect = new Rect(0, 0, minWidth, minHeight);
            grid.WidthRequest = minWidth;
            grid.HeightRequest = minHeight;
            //grid.Arrange(rect); //results int Layout cycle detected.  Layout could not complete.
            System.Diagnostics.Debug.WriteLine($"ArrangeOverride width={minWidth},height={minWidth}");
            return new Size(minWidth, minHeight);
        }
        protected override void OnSizeAllocated(double width, double height)
        {
            base.OnSizeAllocated(width, height);
            System.Diagnostics.Debug.WriteLine($"OnSizeAllocated width={width},height={height}");
        }
    }

xaml代码

<?xml version="1.0" encoding="UTF-8"?>
<ContentView xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             x:Class="CustomLayouts.CardView"
             BackgroundColor="Red">
  <ContentView.Content>
        <Grid x:Name="grid" BackgroundColor="DarkRed">
            <Label Text="1" />
        </Grid>
  </ContentView.Content>
</ContentView>

[Edit]输出如下:

OnSizeAllocated width=-1,height=-1
MeasureOverride width=55,height=85
MeasureOverride width=55,height=85
OnSizeAllocated width=1013,height=0
ArrangeOverride width=55,height=55
MeasureOverride width=55,height=85

grid and cardcontrols size =1013 height=0

我在这里创建了一个示例库:https://github.com/mfe-/CustomLayoutExamples。非常感谢您的帮助。

Answer 1

关于自定义控件的测量和布局有一个开放的问题，这似乎会导致您遇到的问题:https://github.com/dotnet/maui/issues/4019

Answer 2

我认为我计算控件大小的方法错过了重要的一步。我需要设置DesiredSize，以便用正确的值调用ArrangeOverride。

我的代码现在看起来像这样:

protected override Size MeasureOverride(double widthConstraint, double heightConstraint)
    {
        var size = Size.Zero;
        //size is not set, calculate the size dynamicly
        if (WidthRequest == -1 && HeightRequest == -1)
        {
            //calculate size
            size = CalculateCardSize(
                widthConstraint == 0 ? double.PositiveInfinity : widthConstraint,
                heightConstraint == 0 ? double.PositiveInfinity : heightConstraint);
        }
        else
        {
            //if the size of the control was set for example in xaml, we use those values
            size = new Size(WidthRequest, HeightRequest);
        }
        //it looks like the desired size must be set in measureoverride
        this.DesiredSize = size;
        base.MeasureOverride(size.Width, size.Height);
        return size;
    }

上面的代码用正确的值调用了方法protected override Size ArrangeOverride(Rect bounds)。