绑定 XAML uwp 时遇到问题答案

【问题标题】：Trouble binding XAML uwp绑定 XAML uwp 时遇到问题
【发布时间】：2017-01-12 23:57:06
【问题描述】：

您好，我正在学习本教程http://blogs.u2u.be/diederik/post/2011/11/14/null.aspx，将元素的可见性绑定到布尔属性。该程序不工作。代码如下：

<Page.Resources>
    <local:BooleanToVisibilityConverter x:Key="TrueToVisibleConverter"/>
</Page.Resources>

<Grid Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">
    <StackPanel>
        <TextBlock  Text=" Hello World" 
                    Visibility="{Binding Path=Show_element, Converter={StaticResource TrueToVisibleConverter}}"/>
        <Button Click="Button_Click">press button</Button>
    </StackPanel>
</Grid>

public sealed partial class MainPage : Page , INotifyPropertyChanged
{
    private bool show_element ;
    public bool Show_element
    {
        get { return show_element; }
        set
        {
            show_element = value;
            this.OnPropertyChanged();
            Debug.WriteLine("Show_element value changed");
        }
    }
    public MainPage()
    {
        this.InitializeComponent();
    }

    private void Button_Click(object sender, RoutedEventArgs e)
    {
        Show_element = !Show_element;
    }
    public event PropertyChangedEventHandler PropertyChanged = delegate { };
    public void OnPropertyChanged(string propertyName = null)
    {
        this.PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
    }
}
public class BooleanToVisibilityConverter : IValueConverter
{       
    public bool IsReversed { get; set; }

    public object Convert(object value, Type typeName, object parameter, string language)
    {
        var val = System.Convert.ToBoolean(value);
        if (this.IsReversed)
        {
            val = !val;
        }

        if (val)
        {
            return Visibility.Visible;
        }

        return Visibility.Collapsed;
    }

    public object ConvertBack(object value, Type targetType, object parameter, string language)
    {
        throw new NotImplementedException();
    }
}

可见性不会随属性而改变。由于智能感知（Error Xaml namespace），我遇到了一个错误，该错误已解决。不知道这段代码有什么问题。

谢谢。

【问题讨论】：

标签： c# xaml uwp winrt-xaml windows-10-universal

【解决方案1】：

改变

this.OnPropertyChanged();

到

this.OnPropertyChanged("Show_element");

编辑：除此之外，您没有 ViewModel（抱歉，我在检查您的代码时错过了），所以您需要创建一个并将其设置为 DataContext：

ViewModel.cs：

public class ViewModel : INotifyPropertyChanged
{
    private bool show_element;
    public bool Show_element
    {
        get { return show_element; }
        set
        {
            show_element = value;
            this.OnPropertyChanged("Show_element");
            Debug.WriteLine("Show_element value changed");
        }
    }
    public ViewModel()
    {
    }

    public void ButtonClicked()
    {
        Show_element = !Show_element;
    }

    public event PropertyChangedEventHandler PropertyChanged = delegate { };
    public void OnPropertyChanged(string propertyName = null)
    {
        this.PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
    }
}

你的 MainPage.xaml.cs 应该看起来像这样：

public sealed partial class MainPage : Page
{        
    private ViewModel _viewModel;

    public MainPage()
    {
        this.InitializeComponent();
        _viewModel = new ViewModel();
        DataContext = _viewModel;
    }

    private void Button_Click(object sender, RoutedEventArgs e)
    {
        _viewModel.ButtonClicked();
    }        
}

【讨论】：