c# - 当用户在文本框中输入字符时通知 ViewModel

Question

我正在使用 C#、.NET Framework 4.5.1 和 MVVM 模式开发 WPF。

我有这个TextBox :

<TextBox 
    x:Name="userName" 
    HorizontalAlignment="Left" 
    Height="23" 
    TextWrapping="Wrap" 
    VerticalAlignment="Top" 
    Width="231" 
    Margin="10,10,0,5" 
    Text="{Binding Path=UserName, Mode=TwoWay}"/>

这是属性(property):

/// <summary>
/// The <see cref="UserName" /> property's name.
/// </summary>
public const string UserNamePropertyName = "UserName";

private string _userName = null;

/// <summary>
/// Sets and gets the UserName property.
/// Changes to that property's value raise the PropertyChanged event. 
/// </summary>
public string UserName
{
    get
    {
        return _userName;
    }

    set
    {
        if (_userName == value)
        {
            return;
        }

        RaisePropertyChanging(UserNamePropertyName);
        _userName = value;
        RaisePropertyChanged(UserNamePropertyName);
        DoLoginCommand.RaiseCanExecuteChanged();
    }
}

我的问题是直到 TextBox 才能获得新值失去焦点。

有什么方法可以通知 ViewModel当用户在 TextBox 上键入字符时?

Answer 1

在您的绑定(bind)中，指定 UpdateSourceTrigger=PropertyChanged

<TextBox 
    x:Name="userName" 
    HorizontalAlignment="Left" 
    Height="23" 
    TextWrapping="Wrap" 
    VerticalAlignment="Top" 
    Width="231" 
    Margin="10,10,0,5" 
    Text="{Binding Path=UserName, UpdateSourceTrigger=PropertyChanged}"/>