文本框没有被重置，尽管它绑定的属性被设置为 null

Question

我在一个表单上有一个文本框，它的文本属性没有被重置，尽管它绑定的字符串属性被设置为空。访问由表单上另一个名为 cbxPartIINA 的复选框控制。当检查CBXPartiina时，应该禁用文本框并将其清空。当我检查 cbxPartIINA 时，文本框被禁用，但没有空白。

这是文本框的 XAML：

    <TextBox Grid.Row="1" Grid.Column="0" HorizontalAlignment="Left" MaxLength="25" 
                        MinWidth="200" CharacterCasing="Upper" BorderThickness="0" Style="{StaticResource PartIIGridIsEnabledTextBox}"
                        Margin="5,2,0,3" FontWeight="Bold" Name="tbxNewSuspectLastName" 
                        Text="{Binding Form104CModel.NewSuspectLastName, Mode=TwoWay}"/>

这里是静态资源：

       <Style TargetType="TextBox" x:Key="PartIIGridIsEnabledTextBox">
            <!-- This style is used to turn off TextBoxes in Part II-->
            <Style.Triggers>
                <DataTrigger Binding="{Binding IsChecked, ElementName=cbxPartIINA}" Value="False">
                    <Setter Property="IsEnabled" Value="True"/>
                </DataTrigger>
                <DataTrigger Binding="{Binding IsChecked, ElementName=cbxPartIINA}" Value="True">
                    <Setter Property="IsEnabled" Value="False"/>
                    <Setter Property="Text" Value=""/>
                </DataTrigger>
            </Style.Triggers>
            <Setter Property="FontWeight" Value="Bold"></Setter>
        </Style>

这是复选框的 XAML，选中后会关闭文本框：

 <CheckBox Grid.Column="1" Content="NA" Background="White" Height="20" Width="auto" BorderBrush="Black" Name="cbxPartIINA" 
                          IsChecked="{Binding Path=Form104CModel.IsPartIINA, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"/>

这是 textbox.text 绑定到的属性：

    private String newsuspectlastname;
    public String NewSuspectLastName
    {
        get
        {
            return this.newsuspectlastname;
        }
        set
        {
            this.newsuspectlastname = value;
            this.NewSuspect.LastName = value;
        }
    }

尽管绑定是双向的并且基础属性 NewSuspectLastName 被设置为 null，但 textbox.text 属性并未被重置。

Answer 1

WPF 使用 INotifyPropertyChanged 来监控底层模型的变化。

您需要在您的模型上实现 INotofyPropertyChanged，如下所示：

public class MyModel: INotifyPropertyChanged  
{
    public event PropertyChangedEventHandler PropertyChanged;  

    // This method is called by the Set accessor of each property.  
    // The CallerMemberName attribute that is applied to the optional propertyName  
    // parameter causes the property name of the caller to be substituted as an argument.  
    private void NotifyPropertyChanged([CallerMemberName] String propertyName = "")  
    {  
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }  

    private String newsuspectlastname;
    public String NewSuspectLastName
    {
        get
        {
            return this.newsuspectlastname;
        }
        set
        {
            if (value != this.newsuspectlastname )  
             {  
                 this.newsuspectlastname = value;
                 this.NewSuspect.LastName = value;
                 NotifyPropertyChanged();  
            }  

        }
    }
}

Answer 2

这是因为您在对象级别而不是样式级别设置了文本绑定。直接在对象上设置属性总是会优先于 Style 设置的值。为了实现您所需要的，您只需将绑定移动到样式，如下所示：

<Style TargetType="TextBox" x:Key="PartIIGridIsEnabledTextBox">
    <!-- This style is used to turn off TextBoxes in Part II-->
    <Style.Triggers>
        <DataTrigger Binding="{Binding IsChecked, ElementName=cbxPartIINA}" Value="False">
            <Setter Property="IsEnabled" Value="True"/>
        </DataTrigger>
        <DataTrigger Binding="{Binding IsChecked, ElementName=cbxPartIINA}" Value="True">
            <Setter Property="IsEnabled" Value="False"/>
            <Setter Property="Text" Value=""/>
        </DataTrigger>
    </Style.Triggers>
    <Setter Property="FontWeight" Value="Bold"></Setter>
    <Setter Property="Text" Value="{Binding Form104CModel.NewSuspectLastName, Mode=TwoWay}"/>
</Style>

您的文本框将如下所示：

<TextBox Grid.Row="1" Grid.Column="0" HorizontalAlignment="Left" MaxLength="25" MinWidth="200" CharacterCasing="Upper" BorderThickness="0" Style="{StaticResource PartIIGridIsEnabledTextBox}" Margin="5,2,0,3" FontWeight="Bold" Name="tbxNewSuspectLastName"/>