Silverlight中文本框的占位符行为

Question

Silverlight中的文本框是否有任何属性，如html输入标签中的占位符？我想向用户提供一些提示，此文本框将用作输入。例如：加载页面后，TextBox中将出现一个字符串，例如“ search here ...”，并且用户单击TextBox时，该字符串就会消失，并且如果用户在单击时没有插入任何内容，则会再次出现该字符串。此文本框。

Answer 1

这里是如何处理行为：

http://weblogs.asp.net/jdanforth/archive/2010/09/17/silverlight-watermark-textbox-behavior.aspx

Answer 2

我对Johan的水印行为类进行了轻微的修改/增强，因为它不考虑文本字段由于绑定而何时更改。 （即，假设您拥有：

<TextBox Text="{Binding AccountNumber,Mode=TwoWay}">
    <i:Interaction.Behaviors>
        <Behaviors:Placeholder Text="Enter Account #..." Foreground="Gray" />
    </i:Interaction.Behaviors>
</TextBox>

然后在您的视图模型中：

    public string AccountNumber
    {
        get { return _accountNumber; }
        set { _accountNumber = value;
        RaisePropertyChanged("AccountNumber");
        }
    }

现在，如果在代码中的某处执行类似“ AccountNumber = string.Empty”的操作，该行为将更新水印：

public class Placeholder : Behavior<TextBox>
{
    private bool _hasPlaceholder;
    private Brush _textBoxForeground;

    public String Text { get; set; }
    public Brush Foreground { get; set; }

    protected override void OnAttached()
    {
        _textBoxForeground = AssociatedObject.Foreground;

        base.OnAttached();
        if (Text != null)
            SetPlaceholderText();
        AssociatedObject.GotFocus += GotFocus;
        AssociatedObject.LostFocus += LostFocus;
        AssociatedObject.TextChanged += TextChanged;     
    }

    private void TextChanged(object sender, 
        TextChangedEventArgs textChangedEventArgs)
    {
        if (string.IsNullOrWhiteSpace(AssociatedObject.Text) &&
            FocusManager.GetFocusedElement() != AssociatedObject)
        {
            if (Text != null)
                SetPlaceholderText();
        }
    }

    private void LostFocus(object sender, RoutedEventArgs e)
    {
        if (string.IsNullOrWhiteSpace(AssociatedObject.Text))
        {
            if (Text != null)
                SetPlaceholderText();
        }
    }

    private void GotFocus(object sender, RoutedEventArgs e)
    {
        if (_hasPlaceholder)
            RemovePlaceholderText();
    }

    private void RemovePlaceholderText()
    {
        AssociatedObject.Foreground = _textBoxForeground;
        AssociatedObject.Text = "";
        _hasPlaceholder = false;
    }

    private void SetPlaceholderText()
    {
        AssociatedObject.Foreground = Foreground;
        AssociatedObject.Text = Text;
        _hasPlaceholder = true;
    }

    protected override void OnDetaching()
    {
        base.OnDetaching();
        AssociatedObject.GotFocus -= GotFocus;
        AssociatedObject.LostFocus -= LostFocus;
    }
}

Answer 3

为了避免绑定的问题应该在Loaded事件中订阅