在命令中调用时标记属性为空答案

【问题标题】：Tag property is null when called in Command在命令中调用时标记属性为空
【发布时间】：2017-08-07 09:22:58
【问题描述】：

XAML

<UserControl.CommandBindings>
    <CommandBinding Command="{x:Static local:ReturnsUserControl.GetValueCommand}"
                    Executed="ExecutedGetValueCommand"
                    CanExecute="CanExecuteGetValueCommand" />
</UserControl.CommandBindings>
<TextBox x:Name="txtExchangeQuantity" />
<Button Content="Add"
        Tag="{Binding ProductBarcode}"
        Command="{x:Static local:ReturnsUserControl.GetValueCommand}"
        CommandParameter="{Binding Text, ElementName=txtExchangeQuantity}"/>

代码隐藏

public static RoutedCommand GetValueCommand = new RoutedCommand();
private void ExecutedGetValueCommand(object sender, ExecutedRoutedEventArgs e)
{
    Button b = (sender) as Button;
    MessageBox.Show(b.Tag.ToString());
}
private void CanExecuteGetValueCommand(object sender, CanExecuteRoutedEventArgs e)
    e.CanExecute = true;
}

当我单击该按钮时，我收到一个NullException，因为显然Tag 的值为空，但我确信Tag 有一个值。那么如何使用Command 获取Tag 的值？

这是我用来检查Tag是否有东西的：

private void SampleClick(object sender, RoutedEventArgs e)
{
    Button btnSelect = sender as Button;
    string barcode = btnSelect.Tag.ToString();
    MessageBox.Show(barcode);
}

【问题讨论】：

标签： c# wpf data-binding command

【解决方案1】：

您确定ProductBarcode 绑定确实有效吗？以下示例代码当然有效。请参考。

private void ExecutedGetValueCommand(object sender, ExecutedRoutedEventArgs e)
{
    Button btn = e.OriginalSource as Button;
    MessageBox.Show(btn.Tag.ToString());
}

<UserControl>
    <UserControl.CommandBindings>
        <CommandBinding Command="{x:Static local:ReturnsUserControl.GetValueCommand}"
                    Executed="ExecutedGetValueCommand"
                    CanExecute="CanExecuteGetValueCommand" />
    </UserControl.CommandBindings>
    <StackPanel>
        <TextBox x:Name="txtExchangeQuantity" />
        <Button Content="Add"
                        Tag="tag..."
                        Command="{x:Static local:ReturnsUserControl.GetValueCommand}"
                        CommandParameter="{Binding Text, ElementName=txtExchangeQuantity}"/>
    </StackPanel>
</UserControl>

请注意，我使用ExecutedRoutedEventArgs 的OriginalSource 属性。

【讨论】：