Xamarin:用于Android和windows UWP的Xamarin表单中的分组列表的垂直字母索引(跳转列表)

Question

我已经为ios，android和windows平台设计了一个Xamarin表单的分组列表视图。当我在列表视图中设置GroupShortNameBindingproperty时，在IOS中会自动显示垂直索引(跳转列表)。但是跳转列表不会出现在android中。如何在android和windows中使用自定义渲染获得垂直索引的支持。如果任何人可以提供支持此功能跨平台的自定义渲染源代码。

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Answer 1

最简单的方法是使用XAML hack，如果你不需要CustomRenders的话。

您可以将ListView包装在高度和宽度等于父页面(内容页面)的RelativeLayout中。

对于列表视图，使用高度作为父对象，宽度为父对象的90%。添加一个宽度为10%的堆栈布局，从相对布局的90%开始，并将高度作为父级。使其方向垂直。将所有字母表作为标签添加到堆栈布局中，并实现其TapGesture以ScrollTo特定位置。

将Android的宽度设置为90%，iOS和windows保持为100%，堆栈布局宽度为0%，IsVisible=false。

ViewModel：

public class JumpListViewModel : INotifyPropertyChanged
{
    private ObservableCollection<Item> _allItems;
    private List<string> _alphabetList;

    public event PropertyChangedEventHandler PropertyChanged;

    [NotifyPropertyChangedInvocator]
    protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null) => PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));

    public JumpListViewModel()
    {
        AllItems = new ObservableCollection<Item>(new List<Item> { new Item { MyText = "1" }, new Item { MyText = "2" }, new Item { MyText = "3" } });

        AlphabetList = "ABCDEFGHIJKLMNOPQRSTUVWXYZ".ToCharArray().Select(x => x.ToString()).ToList();
    }

    public ObservableCollection<Item> AllItems
    {
        get { return _allItems; }
        set
        {
            _allItems = value;
            OnPropertyChanged();
        }
    }

    public List<string> AlphabetList
    {
        get { return _alphabetList; }
        set
        {
            _alphabetList = value;
            OnPropertyChanged();
        }
    }
}

查看：

<RelativeLayout VerticalOptions="FillAndExpand">

    <ListView VerticalOptions="FillAndExpand" HasUnevenRows="True" ItemsSource="{Binding AllItems}"
              SeparatorColor="Transparent" SeparatorVisibility="None" BackgroundColor="Transparent"
              RelativeLayout.HeightConstraint="{ConstraintExpression Type=RelativeToParent, Property=Height, Factor=1}">
      <RelativeLayout.WidthConstraint>
        <OnPlatform x:TypeArguments="Constraint" Android="{ConstraintExpression Type=RelativeToParent, Property=Width,Factor=0.9}"
                    iOS="{ConstraintExpression Type=RelativeToParent, Property=Width,Factor=1}"
          WinPhone="{ConstraintExpression Type=RelativeToParent, Property=Width,Factor=1}" />
      </RelativeLayout.WidthConstraint>

      <ListView.ItemTemplate>
        <DataTemplate>
          <ViewCell>

            <StackLayout HorizontalOptions="FillAndExpand" BackgroundColor="Silver">

              <Label Text="{Binding MyText}" />
              <Button Text="button" />
              <BoxView HeightRequest="1" Color="Gray" BackgroundColor="Gray" HorizontalOptions="FillAndExpand" />

            </StackLayout>

          </ViewCell>
        </DataTemplate>
      </ListView.ItemTemplate>
    </ListView>

    <ListView VerticalOptions="FillAndExpand" HasUnevenRows="True" ItemsSource="{Binding AlphabetList}"
              SeparatorColor="Transparent" SeparatorVisibility="None" BackgroundColor="Transparent"
              RelativeLayout.HeightConstraint="{ConstraintExpression Type=RelativeToParent, Property=Height, Factor=0.9}"
      RelativeLayout.YConstraint="{ConstraintExpression Type=RelativeToParent, Property=Height, Factor=0.05}"
      RelativeLayout.XConstraint="{ConstraintExpression Type=RelativeToParent, Property=Width, Factor=0.9}">
      <RelativeLayout.WidthConstraint>
        <OnPlatform x:TypeArguments="Constraint" Android="{ConstraintExpression Type=RelativeToParent, Property=Width,Factor=0.1}"
                    iOS="{ConstraintExpression Type=RelativeToParent, Property=Width,Factor=0, Constant=0}"
          WinPhone="{ConstraintExpression Type=RelativeToParent, Property=Width,Factor=0, Constant=0}" />
      </RelativeLayout.WidthConstraint>
      <ListView.IsVisible>
        <OnPlatform x:TypeArguments="x:Boolean" WinPhone="False" iOS="False" Android="True" />
      </ListView.IsVisible>
      <ListView.ItemTemplate>
        <DataTemplate>
          <ViewCell>
            <Label Text="{Binding .}" TextColor="Red" FontSize="Micro" />
          </ViewCell>
        </DataTemplate>
      </ListView.ItemTemplate>
    </ListView>

  </RelativeLayout>

Android截图：

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