Xamarin.Forms ListView在Android上取消选择项目

Question

我有取消选择项目的问题。我希望再次点击stacklayout IsVisible = false;但我不知道为什么我的代码再次点击后无法正常工作。 StackLayout仍然可见

private bool _isVisible;

public new bool IsVisible
{
  get { return _isVisible; }
  set { _isVisible = value; OnPropertyChanged(nameof(IsVisible)); }
}

private void ChallengeList_ItemSelected(object sender, SelectedItemChangedEventArgs e)
{
   if (e.SelectedItem == null)
     return;
   int licz = 0;
   if (e.SelectedItem is MainPage viewModel && licz == 0)
   {
       int li = 0;
       li++;
       viewModel.IsVisible = true;

       if (li == 2)
       {
          viewModel.IsVisible = false;
          licz = 0;
       }
   }
}

的Xaml：

<ListView x:Name="ChallengeList" SeparatorColor="#3d122c" HasUnevenRows="True"
            ItemSelected="ChallengeList_ItemSelected"  RelativeLayout.YConstraint="{ConstraintExpression ElementName=Lab, Constant=0,Factor=1,Property=Height,Type=RelativeToView}"
      RelativeLayout.HeightConstraint="{ConstraintExpression Property=Height,Factor=0.8,Type=RelativeToParent}">
            <ListView.ItemTemplate>
                <DataTemplate>
                    <ViewCell>
                        <StackLayout Orientation="Horizontal"  BackgroundColor="#40FFFFFF" Padding="10">
                            <StackLayout HorizontalOptions="CenterAndExpand">
                                <Label Text="{Binding Title}" TextColor="#ff3f50" FontSize="17" FontAttributes="Bold" HorizontalOptions="Center"/>
                                <StackLayout HorizontalOptions="CenterAndExpand" IsVisible="{Binding IsVisible}" x:Name="More" Padding="5">
                                    <Label Text="sdfghjkhgfdsfghjkljhgfdsadfghjkljhgfdsaSDFGHJKJHGFDSAsdfghjkhgfds" TextColor="#ff3f50" FontSize="17" FontAttributes="Bold" HorizontalOptions="Center"
                                           LineBreakMode="WordWrap"/>
                                </StackLayout>
                            </StackLayout>
                        </StackLayout>
                    </ViewCell>
                </DataTemplate>
            </ListView.ItemTemplate>
</ListView>

Answer 1

由于e.SelectedItem的类型不是MainPage，因此它始终为空。

解决方案：

创建ViewModel：

在ListView项目中添加一个属性，以指示该项目当前是否已被选中：

public class ItemViewModel : BaseViewModel
{
    public string Title { get; set; }

    private bool isVisible;
    public bool IsVisible
    {
        get { return isVisible; }
        set { SetField(ref isVisible, value); }
    }
}

BaseViewModel ：

public class BaseViewModel : INotifyPropertyChanged
{

    public event PropertyChangedEventHandler PropertyChanged;

    protected void OnPropertyChanged([CallerMemberName] string propertyName = null)
    {
        PropertyChangedEventHandler handler = PropertyChanged;
        if (handler != null)
        {
            PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }
    }

    protected bool SetField<T>(ref T field, T value, [CallerMemberName] string propertyName = null)
    {
        if (Object.Equals(field, value)) return false;
        field = value;
        OnPropertyChanged(propertyName);
        return true;
    }
}

然后在页面的ViewModel中，您可以在SelectedItem事件中设置IsSelected的{​​{1}}值：

XAML：

SelectedItem

在<?xml version="1.0" encoding="utf-8" ?> <ContentPage xmlns="http://xamarin.com/schemas/2014/forms" xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml" xmlns:local="clr-namespace:App7" x:Class="App7.MainPage"> <ContentPage.BindingContext> <local:MainViewModel/> </ContentPage.BindingContext> <ListView x:Name="ChallengeList" SeparatorColor="#3d122c" HasUnevenRows="True" ItemsSource="{Binding Title}" SelectedItem="{Binding SelectedItem}" RelativeLayout.YConstraint="{ConstraintExpression ElementName=Lab, Constant=0,Factor=1,Property=Height,Type=RelativeToView}" RelativeLayout.HeightConstraint="{ConstraintExpression Property=Height,Factor=0.8,Type=RelativeToParent}"> <ListView.ItemTemplate> <DataTemplate> <ViewCell> <StackLayout Orientation="Horizontal" BackgroundColor="#40FFFFFF" Padding="10"> <StackLayout HorizontalOptions="CenterAndExpand"> <Label Text="{Binding Title}" TextColor="#ff3f50" FontSize="17" FontAttributes="Bold" HorizontalOptions="Center"/> <StackLayout HorizontalOptions="CenterAndExpand" IsVisible="{Binding IsVisible}" x:Name="More" Padding="5"> <Label Text="QWER" TextColor="#ff3f50" FontSize="17" FontAttributes="Bold" HorizontalOptions="Center" LineBreakMode="WordWrap"/> </StackLayout> </StackLayout> </StackLayout> </ViewCell> </DataTemplate> </ListView.ItemTemplate> </ListView> </ContentPage> ：

中

MainViewModel

效果：

Answer 2

尝试删除变量li和licz，然后切换IsVisible值，如下所示：

private void ChallengeList_ItemSelected(object sender, SelectedItemChangedEventArgs e)
{
   if (e.SelectedItem == null)
     return;

    viewModel.IsVisible = !viewModel.IsVisible;
}