WPF TextBox MaxLength警告

Question

無論如何，當用戶嘗試鍵入比TextBox.MaxLength屬性允許的更多字符時，發出可見和可聽警告嗎？

Answer 1

您可以在綁定上添加ValidationRule。如果驗證失敗，默認ErrorTemplate將用於文本框，否則你也可以自定義...的ValidatonRule的

例如：

class MaxLengthValidator : ValidationRule 
{ 
    public MaxLengthValidator() 
    { 

    } 

    public int MaxLength 
    { 
     get; 
     set; 
    } 


    public override ValidationResult Validate(object value, System.Globalization.CultureInfo cultureInfo) 
    { 
     if (value.ToString().Length <= MaxLength) 
     { 
      return new ValidationResult(true, null); 
     } 
     else 
     { 
      //Here you can also play the sound... 
      return new ValidationResult(false, "too long"); 
     } 

    } 
} 

以及如何將其添加到綁定：

<TextBlock x:Name="target" /> 
<TextBox Height="23" Name="textBox1" Width="120"> 
    <TextBox.Text> 
     <Binding Mode="OneWayToSource" ElementName="target" Path="Text" UpdateSourceTrigger="PropertyChanged"> 
      <Binding.ValidationRules> 
       <local:MaxLengthValidator MaxLength="10" /> 
      </Binding.ValidationRules> 
     </Binding> 
    </TextBox.Text> 
</TextBox>