Question

我希望按钮单击后即可更改标签的可见性。

xaml视图：

<local:ButtonRenderer Text="Connect" BackgroundColor="#6DCFF6" TextColor="White" Command="{Binding viewTemperature}" CornerRadius="10" WidthRequest="200" IsVisible="{Binding !isConnecting}"/>
<Label Text="PlaceholderText" TextDecorations="Underline" TextColor="White" Margin="0,5,0,0" HorizontalTextAlignment="Center" IsVisible="{Binding !isConnecting}"/>

ViewModel

viewTemperature = new Command(async () =>
{
    isConnecting = true;
    await _navigation.PushModalAsync(new TemperaturePage());
}) ;

public bool isConnecting
{
    get
    {
        return _isConnecting;
    }
    set
    {
        _isConnecting = value;
        PropertyChanged?.Invoke(this, new 
        PropertyChangedEventArgs(_isConnecting.ToString()));
    }
}

我在代码中放置了断点，并且在我的视图模型中将isConnected更改为true。但是，我的标签的可见性未更改。我怀疑PropertyChanged是否不应该更改bool值？

Answer 1

您无法执行IsVisible="{Binding !isConnecting}"，此操作将无效。

您可以创建一个InvertBoolConverter，也可以使用更简单的选项“触发器”。这是一个示例：

<Label Text="PlaceholderText" TextDecorations="Underline" TextColor="White" Margin="0,5,0,0" HorizontalTextAlignment="Center" 
            IsVisible="{Binding isConnecting}">
    <Label.Triggers>
        <DataTrigger TargetType="Label" Binding="{Binding isConnecting}" Value="True">
            <Setter Property="IsVisible" Value="False" />
        </DataTrigger>
         <DataTrigger TargetType="Label" Binding="{Binding isConnecting}" Value="False">
            <Setter Property="IsVisible" Value="True" />
        </DataTrigger>
    </Label.Triggers>
</Label>

Answer 2

您可以在ViewModel

中改进代码

public event PropertyChangedEventHandler PropertyChanged;

protected virtual void NotifyPropertyChanged([CallerMemberName] string propertyName = "")
{
  PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
}


private bool isconnecting ;
public bool isConnecting
{
  get
  {
    return isconnecting;
  }

  set
  {
    if (isconnecting != value)
    {
      isconnecting = value;
      NotifyPropertyChanged();
    }
  }
}

从ViewModel返回布尔值到View绑定

2 个答案: