如何在用户键入文本框时启用按钮

为什么每个人都把事情弄得这么复杂!

    <TextBox x:Name="TB"/>
    <Button IsEnabled="{Binding ElementName=TB,Path=Text.Length}">Test</Button>

<TextBox x:Name="txt_Titel />
<Button Content="Transfer" d:IsLocked="True">
  <Button.Style>
    <Style>
      <Style.Triggers>
        <DataTrigger Binding="{Binding ElementName=txt_Titel, Path=Text}" Value="">
         <Setter Property="Button.IsEnabled" Value="false"/>
        </DataTrigger>
      </Style.Triggers>
    </Style>
  </Button.Style>
</Button>

如果您没有使用命令,另一种选择是使用转换器。

例如,使用通用Int-to-Bool转换器:

  [ValueConversion(typeof(int), typeof(bool))]
  public class IntToBoolConverter : IValueConverter
  {
    #region IValueConverter Members

    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
      try
      {
        return (System.Convert.ToInt32(value) > 0);
      }
      catch (InvalidCastException)
      {
        return DependencyProperty.UnsetValue;
      }
    }

    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
      return System.Convert.ToBoolean(value) ? 1 : 0;
    }

    #endregion
  }

然后在按钮IsEnabled属性上:

<Button IsEnabled={Binding ElementName=TextBoxName, Path=Text.Length, Converter={StaticResource IntToBoolConverter}}/>

嗯,,

<TextBox Text={Binding Path=TitleText}/>

<Button Command="{Binding Path=ClearTextCommand}" Content="Clear Text"/>

下面是视图模型中的示例代码

public class MyViewModel : INotifyPropertyChanged
{
    public ICommand ClearTextCommand { get; private set; }

    private string _titleText; 
    public string TitleText
    {
        get { return _titleText; }
        set
        {
            if (value == _titleText)
                return;

            _titleText = value;
            this.OnPropertyChanged("TitleText");
        }
    }   

    public MyViewModel()
    {
        ClearTextCommand = new SimpleCommand
            {
                ExecuteDelegate = x => TitleText="",
                CanExecuteDelegate = x => TitleText.Length > 0
            };  
    }            

    public event PropertyChangedEventHandler PropertyChanged;

    protected void OnPropertyChanged(string propertyName)
    {
        PropertyChangedEventHandler handler = this.PropertyChanged;
        if (handler != null)
            handler(this, new PropertyChangedEventArgs(propertyName));
    }     
}

SimpleCommand

另外,还可以从中查看MVVM项目模板/工具包 http://blogs.msdn.com/llobo/archive/2009/05/01/download-m-v-vm-project-template-toolkit.aspx . 它使用DelegateCommand进行指挥,对于任何项目来说,它都应该是一个很好的开始模板。

这个问题的关键在于绑定本身。。

添加UpdateSourceTrigger=PropertyChanged

向文本框添加一个回调,该文本框在每次笔划时触发。测试该回调中是否为空,并启用/禁用按钮。