CollectionView SelectionChange事件在Android中无法正常工作（.NET MAUI）

Question

我正在尝试在.NET MAUI中创建自定义标签控件，为此，我首先尝试使用ScrollView和BindableStackLayout控件尝试过它，但是在此，我面临问题。

这里报告 solollview bug

，作为另一种方法或工作，我试图使用CollectionView开发相同的选项卡控制。

这种替代方法在iOS中工作正常，但在Android中无法正常工作。

在Android和iOS中都有一个问题。我将BoxView Control作为所选选项卡的指示器。我将仅显示选定的选项卡，但这仅在第一个选项卡中显示，当我单击其他选项卡时，该选项卡会更改，但不会从第一个选项卡中隐藏并在其他选定的选项卡中可见。

我已经为选定状态使用了带有白色的Visual State Manager，因为它看起来像是我尝试使用BoxView创建的指示器。但这也显示仅当该视图获得iOS加载时，我必须先选择选项卡，然后仅在其中显示所选颜色。

这是我所做的：

mainpage.xaml

<ContentPage.Content>

    <Grid RowDefinitions="50, *" RowSpacing="0">

        <CollectionView x:Name="TabsView"
                        Grid.Row="0"
                        ItemsSource="{Binding Tabs,Mode=TwoWay}"
                        ItemsUpdatingScrollMode="KeepItemsInView"
                        ItemSizingStrategy="MeasureAllItems"
                        SelectedItem="{Binding SelectedTab}"
                        SelectionChangedCommand="{Binding Path=BindingContext.TabChangedCommand,Source={x:Reference TabsView}}"
                        SelectionChangedCommandParameter="{Binding SelectedTab}"
                        SelectionMode="Single">

            <CollectionView.ItemsLayout>
                <LinearItemsLayout Orientation="Horizontal"/>
            </CollectionView.ItemsLayout>

            <CollectionView.ItemTemplate>
                <DataTemplate>
                    <Grid RowSpacing="0" RowDefinitions="*, 3">
                        
                        <Label Grid.Row="0"
                                    Text="{Binding TabTitle}"
                                    TextColor="White"
                                    BackgroundColor="navy"
                                    Padding="20,0"
                                    VerticalTextAlignment="Center"
                                    HorizontalTextAlignment="Center"
                                    FontSize="12" />
                        <BoxView Grid.Row="1" Color="{Binding BoxColor}"
                                    IsVisible="{Binding IsSelected}"/>
                        <VisualStateManager.VisualStateGroups>
                            <VisualStateGroup Name="CommonStates">
                                <VisualState Name="Normal"/>
                                <VisualState Name="Selected">
                                    <VisualState.Setters>
                                        <Setter Property="BackgroundColor" Value="White" />
                                    </VisualState.Setters>
                                </VisualState>
                            </VisualStateGroup>
                        </VisualStateManager.VisualStateGroups>
                    </Grid>
                </DataTemplate>

            </CollectionView.ItemTemplate>
        </CollectionView>

        
        <tabs:ParentRecordTabView Grid.Row="1"
                                    IsVisible="{Binding IsParentRecordTabVisible}"
                                    VerticalOptions="FillAndExpand"/>

        <tabs:AdditionalInfoTabView Grid.Row="1"
                                    IsVisible="{Binding IsAdditionalInfoTabVisible}"
                                    VerticalOptions="FillAndExpand" />
        


    </Grid>

</ContentPage.Content>

---

mainpageViewModel.cs

public class MainPageViewModel : BaseViewModel
{
    public MainPageViewModel()
    {
        GetTabs();
    }

    private bool _isParentRecordTabVisible = true;
    private bool _isAdditionalInfoTabVisible;

    private ObservableCollection<TabViewModel> _tabs { get; set; }
    private TabViewModel _selectedTab { get; set; }

    public bool IsParentRecordTabVisible
    {
        get => _isParentRecordTabVisible;
        set { _isParentRecordTabVisible = value; OnPropertyChanged(nameof(IsParentRecordTabVisible)); }
    }

    public bool IsAdditionalInfoTabVisible
    {
        get => _isAdditionalInfoTabVisible;
        set { _isAdditionalInfoTabVisible = value; OnPropertyChanged(nameof(IsAdditionalInfoTabVisible)); }
    }

    public ObservableCollection<TabViewModel> Tabs
    {
        get => _tabs;
        set { _tabs = value; OnPropertyChanged(nameof(Tabs)); }
    }

    public TabViewModel SelectedTab
    {
        get => _selectedTab;
        set
        {
            _selectedTab = value;
            OnPropertyChanged(nameof(SelectedTab));
        }
    }

    public ICommand TabChangedCommand { get { return new Command<TabViewModel>(ChangeTabClick); } }

    private void GetTabs()
    {
        Tabs = new ObservableCollection<TabViewModel>();
        Tabs.Add(new TabViewModel { TabId = 1, IsSelected = true, TabTitle = "Parent record" });
        Tabs.Add(new TabViewModel { TabId = 2, TabTitle = "Additional Info" });
        Tabs.Add(new TabViewModel { TabId = 3, TabTitle = "Contacts" });
        Tabs.Add(new TabViewModel { TabId = 4, TabTitle = "Previous inspections" });
        Tabs.Add(new TabViewModel { TabId = 5, TabTitle = "Attachments" });

        SelectedTab = Tabs.FirstOrDefault();
    }

    public void ChangeTabClick(TabViewModel tab)
    {
        Tabs.All((arg) =>
        {
            if (arg.TabId == tab.TabId)
            {
                arg.IsSelected = true;
            }
            else
            {
                arg.IsSelected = false;
            }
            return true;
        });
        SelectedTab = Tabs.Where(t => t.IsSelected == true).FirstOrDefault();

        switch (SelectedTab.TabId)
        {
            case 1:
                IsParentRecordTabVisible = true;
                IsAdditionalInfoTabVisible = false;
                break;
            case 2:
                IsParentRecordTabVisible = false;
                IsAdditionalInfoTabVisible = true;
                break;
        }
    }
}

---

tabviewmodel.cs

public class TabViewModel : BaseViewModel
{
    private bool _IsSelected;
    public bool IsSelected
    {
        get { return _IsSelected; }
        set
        {
            _IsSelected = value;
            OnPropertyChanged(nameof(IsSelected));
        }
    }

    private int _TabId;
    public int TabId
    {
        get { return _TabId; }
        set
        {
            _TabId = value;
            OnPropertyChanged(nameof(TabId));
        }
    }

    private string _TabTitle;
    public string TabTitle
    {
        get { return _TabTitle; }
        set
        {
            _TabTitle = value;
            OnPropertyChanged(nameof(TabTitle));
        }
    }
}

注意：这种相同的方法在xamarin.forms.forms（Visual Studio 2019）中再次正常工作，这只是在MAUI中不起作用，所以有人注意到类似这样的东西吗？

如何重现错误：检查github

Answer 1

1. 删除项目中的BoxView默认样式。资源＆gt;样式＆gt; styles.xml

    ＆lt; style targetType =“ boxView”＆gt;
    ＆lt; setter property =“ color” value =“ {appthemebinding light = {staticResource gray950}，dark = {staticResource gray200}}” /＆gt;
    

2. 您可以使用iSVisible属性显示boxview是否而不是用boxColor绑定颜色。删除selectionChangedCommand，selectionChangedCommandParameter和VisualStateManager.VisalStateGroups in Collection> Collection> Collection view以及。

   >

    ＆lt; boxview grid.row =“ 1”
                             颜色=“黄色”                                 
                             Isvisible =“ {binding Isselected}”/＆gt;
    

3. 设置selectedtab属性如下。

     public tabViewModel selectedtab
    {
        get =＆gt; _selectedTab;
        放
        {
            _selectedTab = value;
            setSelection（）;
            onProperTychanged（nameof（selectedTab））;
        }
    }
   
     私有void setSelection（）
    {             
        foreach（选项卡中的var项目）
        {
            item.isselected = false;
        }
        selectedtab.isselected = true;
    }