WPF驗證之——必填驗證

要事先必填驗證，首先要重寫ValidationRule類的Validate方法，然後在Binding中指定對應的ValidationRule。

第一步：重寫ValidationRule的Validate

public class RequiredValidationRule:ValidationRule {

	public override ValidationResult Validate(object value, System.Globalization.CultureInfo cultureInfo) {
		if (value == null || string.IsNullOrWhiteSpace(value.ToString())) {
			return new ValidationResult(false, "內容不能爲空");
		}
		return new ValidationResult(true, null);
	}
}

第二步：窗體：

<TextBox Grid.Row="0" Grid.Column="1" 
			Validation.ErrorTemplate="{StaticResource CT_TextBox_Required}"
			Style="{StaticResource Style_TextBox_Error}"
	<TextBox.Text>
		<Binding Path="Name" UpdateSourceTrigger="PropertyChanged">
			<Binding.ValidationRules>
				<vr:RequiredValidationRule />
			</Binding.ValidationRules>
		</Binding>
	</TextBox.Text>
</TextBox>

第三步：錯誤控件的樣式

<ControlTemplate x:Key="CT_TextBox_Required">
	<DockPanel>
		<TextBlock Foreground="Red" FontSize="20" Text="!" />
		<AdornedElementPlaceholder />
	</DockPanel>
</ControlTemplate>
<Style x:Key="Style_TextBox_Error" TargetType="{x:Type TextBox}">
	<Setter Property="Margin" Value="10,5,20,5" />
	<Style.Triggers>
		<Trigger Property="Validation.HasError" Value="true">
			<Setter Property="ToolTip"
					Value="{Binding RelativeSource={x:Static RelativeSource.Self},Path=(Validation.Errors)[0].ErrorContent}" />
		</Trigger>
	</Style.Triggers>
</Style>

我們來看看效果圖：，貌似不錯，但是還有不盡人意之處。在控件Focus時，控件內容爲空，我希望此時就顯示錯誤提示，而不是更改後再顯示錯誤提示，首先要添加PreviewGotKeyboardFocus事件

private void TextBox_PreviewGotKeyboardFocus(object sender, KeyboardFocusChangedEventArgs e) {
	TextBox tb = sender as TextBox;
	tb.GetBindingExpression(TextBox.TextProperty).UpdateSource();
}

好，我們輕鬆地實現了必填驗證。

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