如何在 Xamarin.Forms 的列表视图中获取所选项目的坐标? [英] How to get coordinates of the selected item in a list view in Xamarin.Forms?

问题描述

我想获取列表视图中所选项目相对于屏幕的坐标(矩形边界:x、y、宽度和高度)(假设列表视图填满整个屏幕)，以便我可以在该位置并为其设置动画以在我的 Xamarin.Forms 应用中显示所选项目的一些详细信息.

I want to get the coordinates (rectangle bounds: x, y, width and height) of the selected item in the listview relative to the screen (assume the listview fills the whole screen), so that I can create an object at that location and animate it to display some details of the selected item in my Xamarin.Forms app.

xaml 中的列表视图:

listview in xaml:

<ListView ItemTapped="ItemTapped"
    AbsoluteLayout.LayoutFlags="All"
    AbsoluteLayout.LayoutBounds="0.5, 0.5, 1.0, 1.0">
    <ListView.ItemTemplate>
        <DataTemplate>
            <ViewCell Height="50">              
                <AbsoluteLayout>
                    <Label Text="{Binding Info}"
                        AbsoluteLayout.LayoutFlags="All"
                        AbsoluteLayout.LayoutBounds="0.1, 0.5, 0.7, 0.5"/>
                </AbsoluteLayout>
            </ViewCell>
        </DataTemplate>
    </ListView.ItemTemplate>
</ListView>

ItemTapped 事件的 c# 代码:

c# code for ItemTapped event:

void ItemTapped(object sender, EventArgs args)
{
    var listView = (ListView)sender; // the listview
    var selectedItem = args.Item; // the selected item

    // need to get selected item coordinates for the animation
    var selectedItemBounds = ...

    ...
}

最终我想在 Xamarin.Forms 中使用列表视图创建类似这样的内容(列表视图中的对象数量各不相同):

Eventually I want to create somehting like this in Xamarin.Forms with a listview (the number of objects in the listview varies):

推荐答案

一个简单的想法:

有一个作为单例运行的视图助手服务:

Have a view helper service which runs as a singleton:

interface IViewHelper
{
   Rect GetScreenCoordinates(View view);
}

在 ListView 项模板和点击事件处理程序调用中的 AbsoluteLayout 上添加点击手势:

Have a tap gesture added on the AbsoluteLayout you have in the ListView item template, and in the tap event handler call:

IViewHelper viewHelper = CrossViewHelper.Instance; 
Rect rcItem = viewHelper.GetScreenCoordinates((View)sender);

服务 GetScreenCoordinates 的本机实现做了两件事:

The native implementation of the service GetScreenCoordinates does two things:

// Get the native view from the Xamarin Forms view 
var nativeView = Platform.GetRenderer(view);

// Call native functions to get screen coordinates
Android: nativeView.GetLocationOnScreen(coords)
iOS: Use nativeView.ConvertPoint(coords, null)

见https://forums.xamarin.com/discussion/86941/get-xy-co-ordinates-in-tap-gesture-inside-listview

https:///github.com/xamarin/Xamarin.Forms/blob/master/Xamarin.Forms.Platform.Android/PlatformRenderer.cs#L53

另见:https://michaelridland.com/xamarin/creating-native-view-xamarin-forms-viewpage/

我没有完整的代码，但我希望这可以帮助您.

I don't have a complete code, but I hope this can help you.

我认为最后，在您实现动画并显示视图之后，您可以将实现重构为一个很好的行为，您可以附加到任何视图，它是否在列表视图中并不重要，它会只是工作.

I think in the end, after you implement animating and showing the view, you can refactor the implementation into a nice Behavior you can attach to any view, it won't matter if it's inside list-view or not, it will just work.

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