是否可以从ViewModel打开Expander ?

Question

我有一个Expander在我的视图，每次我触摸它打开并显示数据。是否可以打开Expander或关闭它从ViewModel?我想做的是，Expander可以打开或关闭它按下一个Button。

MainPage.xaml:

<StackLayout>
<StackLayout>
<CollectionView>
<CollectionView.ItemTemplate>
<DataTemplate>
<ContentView>
<Frame>
<StackLayout>
<Expander x:Name="expander"></Expander>
</StackLayout>
</Frame>
</ContentView>
</DataTemplate>
</CollectionView.ItemTemplate>
</CollectionView>
</StackLayout>
<StackLayout>
<ImageButton Source="img1" Command="{Binding xxxCommand}" CommandParameter="{Binding Source={x:Reference expander}, Path=.}"/>
</StackLayout>
</StackLayout>

ViewModel:

xxxCommand = new Command((sender)=> {
var exp = sender as Expander;
exp.IsExpanded = !exp.IsExpanded;
//...

});

当我打开应用程序时，我得到这个异常:

Xamarin.Forms.Xaml。找不到对象由扩展器引用

Answer 1

您可以将Expander作为参数传递给按钮的Command。

设置Expander的名称

<Expander x:Name="exp">

<Button Text="XXX"  Command="{Binding xxxCommand}" CommandParameter="{Binding Source={x:Reference exp}, Path=.}" />

在ViewModel

xxxCommand = new Command((sender)=> {
var exp = sender as Expander;
exp.IsExpanded = !exp.IsExpanded;
//...

});

更新在你的情况下，你可以使用数据绑定

<StackLayout>
<Expander  IsExpanded="{Binding IsExpanded}"></Expander>
</StackLayout>

<ImageButton Source="img1" Command="{Binding xxxCommand}"/>

在你的模型中添加一个新属性

public class YourModel : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
public void OnPropertyChanged(string propertyname)
{
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyname));
}
public bool isExpanded;
public bool IsExpanded
{
get { return isExpanded; }
set
{
isExpanded= value;
OnPropertyChanged("IsExpanded");
}
}

//...other properties
}

在ViewModel

//list here is the ItemsSource of your listview
ObservableCollection<YourModel> list = new ObservableCollection<YourModel>();
//list.Add();
//list.Add();
//list.Add();
//list.Add();

Command xxxCommand = new Command(()=> {
//if you want to open the first Expander  
list[0].IsExpanded = true;

});