UWP C++ 通过 EventHandler 自 canvas 移除

Question

我有一个 UWP C++ 应用程序，用户可以在其中向 canvas 添加形状。我希望他们能够使用 Surface 触控笔上的橡皮擦将其删除。

项目已成功添加到 canvas 这样...

if (e->Pointer->PointerDeviceType == Windows::Devices::Input::PointerDeviceType::Pen) {

    auto Translate = ref new TranslateTransform();
    auto ellipse = ref new Ellipse();

    PointerPoint^ p = e->GetCurrentPoint(imgCanvas);

    Translate->X = p->Position.X - Radius/2;
    Translate->Y = p->Position.Y - Radius/2;

    ellipse->Fill = ref new SolidColorBrush(ColorHelper::FromArgb(127, 255, 255, 0));
    ellipse->Width = Radius;
    ellipse->Height = Radius;

    ellipse->Stroke = ref new SolidColorBrush(Colors::Black);
    ellipse->StrokeThickness = 1;

    ellipse->RenderTransform = Translate;
    ellipse->PointerPressed += ref new Windows::UI::Xaml::Input::PointerEventHandler(this, &MainPage::onEllipseTouched);

    Canvas->Children->Append(ellipse);
}

我有以下函数，触摸时调用成功

MainPage::onEllipseTouched(Platform::Object^ sender, Windows::UI::Xaml::Input::PointerRoutedEventArgs^ e)
{
    //check for eraser
    PointerPoint^ p = e->GetCurrentPoint(Canvas);
    if (p->Properties->IsEraser) {
        //NEED TO REMOVE ITSELF FROM
        //Canvas->Children->RemoveAt(i);
        //but obviously I don't know I...
    }
}

如何让椭圆从子列表中删除自身？
另一种方法是遍历 canvas 中的所有 Children 并计算最接近的。这听起来不像使用 EventHandler 那样干净。

编辑

我发现这个示例 Adding an ellipse to mouse position? 还包含一个完全按照我尝试执行的方式删除的示例，但它在 C# 中，其中函数

GridCanvas.Children.Remove(ellipse);

存在。但是我在 C++ 中找不到等价物。

Answer 1

However I can't find and equivalent in C++.

C++ 目前似乎不支持 Remove() 方法。你应该可以先使用RemoveAt(UInt32) as you tried. But you may not know the index of current ellipse, in that case you need to invoke IndexOf(UIElement, UInt32)方法获取索引，然后你可以使用RemoveAt。示例代码如下：

//Get current tapped ellipse.
Ellipse^ currentellipse = dynamic_cast<Ellipse^>(sender);
unsigned int currentindex;   
canvas->Children->IndexOf(currentellipse, &currentindex);
canvas->Children->RemoveAt(currentindex);

UWP C++ 通过 EventHandler 自 canvas 移除

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