Question

以MVVM的Xamarin形式；我正在使用可观察的集合在列表视图中列出我的项目。工作正常。在我的列表视图中，我有一个Label，并且当用户单击该选定列表项时，我需要更改Label值。它也工作正常。但是问题是，只有在我滚动列表视图之后，“选定列表项”的标签值才更改。

我需要按时更改所选列表项的标签值。

这是我的代码： Xaml

<ListView x:Name="Listitem"  Grid.Row="2" Grid.ColumnSpan="2" ItemsSource="{Binding States,Mode=TwoWay}" SelectedItem="{Binding YourSelectedItem,Mode=TwoWay}"  VerticalOptions="FillAndExpand" HasUnevenRows="true" CachingStrategy="RecycleElement" BackgroundColor="White" >
    <ListView.Header>                                                    
        <Grid BackgroundColor="{StaticResource Accent}">
            <Grid.ColumnDefinitions>
                <ColumnDefinition Width="*" />
                <ColumnDefinition Width="*" />
                <ColumnDefinition Width="*" />
            </Grid.ColumnDefinitions>
            <Label Grid.Column="0" Text="Country Code" HorizontalOptions="Center" VerticalOptions="Center" TextColor="{StaticResource Primary}" />
            <Label Grid.Column="1" Text="Name"  HorizontalOptions="Center" TextColor="{StaticResource Primary}" />
            <Label Grid.Column="2" Text="Capital"  HorizontalOptions="Center" TextColor="{StaticResource Primary}" />
        </Grid>
    </ListView.Header>
    <ListView.ItemTemplate>
        <DataTemplate>
            <ViewCell>
                <ViewCell.View>
                    <Grid VerticalOptions="Center">
                        <Grid.ColumnDefinitions>
                            <ColumnDefinition Width="3*" />
                            <ColumnDefinition Width="3*" />
                            <ColumnDefinition Width="3*" />
                            <ColumnDefinition Width="1*" />
                        </Grid.ColumnDefinitions>
                        <Label Grid.Column="0" Text="{Binding abbr}" Margin="5" HorizontalOptions="Center" VerticalOptions="Center" FontSize="18" TextColor="{StaticResource Primary}" />
                        <Label Grid.Column="1" Text="{Binding name}"  Margin="5" HorizontalTextAlignment="Start"  VerticalOptions="Center" FontSize="18" LineBreakMode="WordWrap" TextColor="{StaticResource Primary}"/>
                        <Label Grid.Column="2" Text="{Binding capital}"  Margin="5" HorizontalTextAlignment="Start"  VerticalOptions="Center" FontSize="18" LineBreakMode="WordWrap" TextColor="{StaticResource Primary}"/>
                        <controls:CheckBox Grid.Column="3" Margin="0, 0, 0, 0" CheckedChanged="Handle_CheckedChanged" BindingContext="{Binding .}"  BackgroundColor="Transparent" WidthRequest="40" HeightRequest="30" IsVisible="True" />
                    </Grid>
                </ViewCell.View>
            </ViewCell>
        </DataTemplate>
    </ListView.ItemTemplate>
</ListView>

这是我的选定列表项的View模型；

public TodoItem YourSelectedItem
{
    get
    {
        return _yourSelectedItem;
    }

    set
    {
        _yourSelectedItem = value;
        _yourSelectedItem.abbr = "Tapped";
        OnPropertyChanged("YourSelectedItem");
    }
}

项目来源属性；

private ObservableCollection<TodoItem> _States;

public ObservableCollection<TodoItem> States
{ 
    get { return _States; }
    set { _States = value; OnPropertyChanged("States"); }  
}

Answer 1

TodoItem类需要实现INotifyPropertyChanged接口，而属性abbr必须像打击一样实现：

public string abbr {
        get 
        { 
            return _abbr; 
        }
        set 
        { 
            if (_abbr != value) {
                _abbr = value;
                OnPropertyChanged("abbr");
            }
        } 

}

列表视图所选项目的值更改未及时反映UI

1 个答案: