如何显示默认文字“ - 选择小组 - ”在WPF中的pageload上的组合框中？ [英] How to display default text "--Select Team --" in combo box on pageload in WPF?

问题描述

在WPF应用程序中，在MVP应用程序中，我有一个组合框，为此我显示从数据库获取的数据。在添加到组合框之前，我要显示默认文本，例如

- 选择团队 - p>

，因此在页面加载时会显示，在选择文本时应清除文本，并显示项目。

正在从DB选择数据。我需要显示默认文本，直到用户从组合框中选择一个项目。

请指导我

解决方案

您可以使用 IValueConverter 在没有任何代码的情况下执行此操作。

 < Grid> 
< ComboBox 
 x：Name =comboBox1
 ItemsSource ={Binding MyItemSource}/> 
< TextBlock 
 Visibility ={Binding SelectedItem，ElementName = comboBox1，Converter = {StaticResource NullToVisibilityConverter}}
 IsHitTestVisible =False
 Text =... Select Team .../> 
< / Grid> 
  

这里有你可以重用的转换器类。

public class NullToVisibilityConverter：IValueConverter
{
#region IValueConverter的实现

public object Convert（object value，类型targetType，对象参数，CultureInfo文化）
{
返回值== null？ Visibility.Visible：Visibility.Collapsed;
}

public object ConvertBack（object value，Type targetType，object parameter，CultureInfo culture）
{
throw new NotImplementedException（）;
}

#endregion
}


 <转换器：NullToVisibilityConverter x：Key =NullToVisibilityConverter > 
  

其中Converters是放置转换器类的地方。例如：

  xmlns：Converters =clr-namespace：MyProject.Resources.Converters
  

这种方法的好处在于你的代码中不会重复代码。

In a WPF app, in MVP app, I have a combo box,for which I display the data fetched from Database. Before the items added to the Combo box, I want to display the default text such as

" -- Select Team --"

so that on pageload it displays and on selecting it the text should be cleared and the items should be displayed.

Selecting data from DB is happening. I need to display the default text until the user selects an item from combo box.

Please guide me

解决方案

You can do this without any code behind by using a IValueConverter.

<Grid>
   <ComboBox
       x:Name="comboBox1"
       ItemsSource="{Binding MyItemSource}"  />
   <TextBlock
       Visibility="{Binding SelectedItem, ElementName=comboBox1, Converter={StaticResource NullToVisibilityConverter}}"
       IsHitTestVisible="False"
       Text="... Select Team ..." />
</Grid>

Here you have the converter class that you can re-use.

public class NullToVisibilityConverter : IValueConverter
{
    #region Implementation of IValueConverter

    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        return value == null ? Visibility.Visible : Visibility.Collapsed;
    }

    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
        throw new NotImplementedException();
    }

    #endregion
}

And finally, you need to declare your converter in a resource section.

<Converters:NullToVisibilityConverter x:Key="NullToVisibilityConverter" />

Where Converters is the place you have placed the converter class. An example is:

xmlns:Converters="clr-namespace:MyProject.Resources.Converters"

The very nice thing about this approach is no repetition of code in your code behind.

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