了解 WidthRequest [英] Understanding WidthRequest

问题描述

我想更改 WidthRequest.因此我注意到这并没有真正设置元素的 width.而是一种提议.

I want to change the WidthRequest. Thereby I noticed that this doesn't really set the width of an element. Rather it is kind of a proposal.

示例:我有一个 ListView 作为子项添加到 StackLayout.我正在为 ListView 设置一个 WidthRequest，但结果不是我所期望的.

Example: I have a ListView added as child to a StackLayout. I'm setting a WidthRequest for the ListView, but the result is not what I expect.

this.listView = new ListView
{
    ItemsSource = new List<IconMenu>
    {
        // creation of some entries
        // ...
    },
    ItemTemplate = new DataTemplate(typeof(IconMenuCell)),
    RowHeight = 44,
    // HERE is the problematic code!
    WidthRequest = 10,
};

Content = new StackLayout
{
    Orientation = StackOrientation.Horizontal,
    Children = {
        this.listView,
        this.detailView,
    },
};

这是IconMenuCell的结构/布局:

public IconMenuCell()
{
    var icon = new Image
    {
        Aspect = Aspect.AspectFit,
        WidthRequest = 40,
    };
    icon.SetBinding(Image.SourceProperty, "IconSource");

    this.textLabel = new Label {
        TextColor = Color.Gray,
        FontSize = 10,
        VerticalOptions = LayoutOptions.Center,
    };
    this.textLabel.SetBinding(Label.TextProperty, "Text");

    View = new StackLayout
    {
        Orientation = StackOrientation.Horizontal,
        Children =
        {
            icon,
            this.textLabel,
        },
    };
}

将 WidthRequest 设置为 10 没有意义，因为图标本身应该占用 40.但在这里我得到了整个列表视图的最小宽度.

Setting the WidthRequest to 10 doesn't make sense, because the icon itself should take 40. But here I get the smallest width for the whole list view.

如果我将 WidthRequest 设置为 60 或 120，则没有区别.结果宽度相同(而不是我想要的宽度).

There is no difference if I set WidthRequest to 60 or 120. The resulting width is the same (and not what I want).

WidthRequest 在这里如何工作?我是否必须更改一些 LayoutOptions?

How does WidthRequest work here? Do I have to change some LayoutOptions?

推荐答案

WidthRequest 只是描述了在下一个布局周期中元素所需的宽度.
要使其按预期工作，必须满足 2 个条件:
1) 请求的宽度与所有约束(例如父级的宽度)和
一致2)触发一个布局周期.
宽度请求:https://developer.xamarin.com/api/property/Xamarin.Forms.VisualElement.WidthRequest/

WidthRequest just describes an element's desired width during the next layout cycle.
For it to work as you'd expect, 2 conditions must be satisfied:
1) the requested width is consistent with all constraits (ex. parent's width) and
2) a layout cycle is triggered.
WidthRequest: https://developer.xamarin.com/api/property/Xamarin.Forms.VisualElement.WidthRequest/

但这很复杂.我建议只用网格替换堆栈布局，并将每个元素放在所需宽度的列中.
网格示例:https://developer.xamarin.com/api/type/Xamarin.Forms.Grid/

But that's complicated. I'd recommend just replacing the stack layout with a grid, and putting each element in a column of the desired width.
Grid Example: https://developer.xamarin.com/api/type/Xamarin.Forms.Grid/

这篇关于了解 WidthRequest的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！