需要基于第二个 ComboBox 的 SelectedValue 设置 WPF MVVM ComboBox ItemsSource 的简单工作示例 [英] Need SIMPLE working example of setting WPF MVVM ComboBox ItemsSource based on SelectedValue of second ComboBox
问题描述
谁能给我看一个 WPF MVVM 应用程序的简单工作示例，以根据 ComboBox A 的 SelectedItem 设置组合框 B 的 ItemsSource?
Can anyone show me a simple working example for a WPF MVVM application to set the ItemsSource of combobox B based on the SelectedItem of ComboBox A?
从我在这个网站上发现的情况来看，它似乎变得太复杂了.
It seems from what I've found on this site that it gets all too complicated all too quickly.
完成它的正确"MVVM 方法是什么?
What's the "right" MVVM way to get it done?
谢谢.
编辑我使用 Didier 的示例进行了更新.我的 XAML 的摘录:
EDIT I updated using Didier's example. An extract of my XAML:
<ComboBox Name="BrowserStackDesktopOS" ItemsSource="Binding Platforms.AvailableBrowserStackDesktopOSes}" SelectedIndex="0" SelectedItem="{Binding Platforms.BrowserStackDesktopOSSelectedValue, Mode=TwoWay}"/>
<ComboBox Name="BrowserStackDesktopOSVersion" ItemsSource="{Binding Platforms.AvailableBrowserStackDesktopOSVersions}" SelectedIndex="0" SelectedItem="{Binding Platforms.BrowserStackDesktopOSVersionSelectedValue, Mode=TwoWay}"/>
<ComboBox Name="BrowserStackDesktopBrowser" ItemsSource="{Binding Platforms.AvailableBrowserStackDesktopBrowsers}" SelectedIndex="0" SelectedItem="{Binding Platforms.BrowserStackDesktopBrowserSelectedValue, Mode=TwoWay}"/>
<ComboBox Name="BrowserStackDesktopBrowserVersion" ItemsSource="{Binding Platforms.AvailableBrowserStackDesktopBrowserVersions}" SelectedIndex="0" SelectedItem="{Binding Platforms.BrowserStackDesktopBrowserVersionSelectedValue, Mode=TwoWay}"/>
以及我背后的代码示例:
And an example of my code behind:
public string BrowserStackDesktopOSSelectedValue {
get { return (string)GetValue(BrowserStackDesktopOSSelectedValueProperty); }
set { SetValue(BrowserStackDesktopOSSelectedValueProperty, value);
AvailableBrowserStackDesktopOSVersions = AvailableBrowserStackDesktopPlatforms.GetOSVersions(BrowserStackDesktopOSSelectedValue);
NotifyPropertyChanged("BrowserStackDesktopOSSelectedValue");
}
}
但是，当我为第一个 ComboBox 选择一个值时，什么也没有发生.我想要填充下一个 ComboBox 的 Itemsource.
However when I select a value for the first ComboBox nothing happens. I am wanting the Itemsource of the next ComboBox to by populated.
我做错了什么?
推荐答案
基本上，您需要在 MVVM 2 中公开组合框选择的值集合和选定值的两个属性.
Basically you need to expose in your MVVM 2 collections of values for combo-box choices and two properties for selected values.
一开始只有第一个集合，如果填充了值.当第一个选定的值更改时，第二个集合将填充适当的值.这是一个示例实现:
In the beginning only the first collection if filled with values. When the first selected value changes the second collection will be filled in with appropriate values. Here is an example implementation:
背后的代码:
public partial class MainWindow : Window
{
public MainWindow()
{
InitializeComponent();
//Set the data context of the window
DataContext = new TestVM();
}
}
public class TestVM : INotifyPropertyChanged
{
#region Class attributes
protected static string[] firstComboValues = new string[] { "Choice_1", "Choice_2" };
protected static string[][] secondComboValues =
new string[][] {
new string[] { "value_1_1", "value_1_2", "value_1_3" },
new string[] { "value_2_1", "value_2_2", "value_2_3" }
};
#endregion
#region Public Properties
#region FirstSelectedValue
protected string m_FirstSelectedValue;
/// <summary>
///
/// </summary>
public string FirstSelectedValue
{
get { return m_FirstSelectedValue; }
set
{
if (m_FirstSelectedValue != value)
{
m_FirstSelectedValue = value;
UpdateSecondComboValues();
NotifyPropertyChanged("FirstSelectedValue");
}
}
}
#endregion
#region SecondSelectedValue
protected string m_SecondSelectedValue;
/// <summary>
///
/// </summary>
public string SecondSelectedValue
{
get { return m_SecondSelectedValue; }
set
{
if (m_SecondSelectedValue != value)
{
m_SecondSelectedValue = value;
NotifyPropertyChanged("SecondSelectedValue");
}
}
}
#endregion
#region FirstComboValues
protected ObservableCollection<string> m_FirstComboValues;
/// <summary>
///
/// </summary>
public ObservableCollection<string> FirstComboValues
{
get { return m_FirstComboValues; }
set
{
if (m_FirstComboValues != value)
{
m_FirstComboValues = value;
NotifyPropertyChanged("FirstComboValues");
}
}
}
#endregion
#region SecondComboValues
protected ObservableCollection<string> m_SecondComboValues;
/// <summary>
///
/// </summary>
public ObservableCollection<string> SecondComboValues
{
get { return m_SecondComboValues; }
set
{
if (m_SecondComboValues != value)
{
m_SecondComboValues = value;
NotifyPropertyChanged("SecondComboValues");
}
}
}
#endregion
#endregion
public TestVM()
{
FirstComboValues = new ObservableCollection<string>(firstComboValues);
}
/// <summary>
/// Update the collection of values for the second combo box
/// </summary>
protected void UpdateSecondComboValues()
{
int firstComboChoice;
for (firstComboChoice = 0; firstComboChoice < firstComboValues.Length; firstComboChoice++)
{
if (firstComboValues[firstComboChoice] == FirstSelectedValue)
break;
}
if (firstComboChoice == firstComboValues.Length)// just in case of a bug
SecondComboValues = null;
else
SecondComboValues = new ObservableCollection<string>(secondComboValues[firstComboChoice]);
}
#region INotifyPropertyChanged implementation
public event PropertyChangedEventHandler PropertyChanged;
protected void NotifyPropertyChanged(string propertyName)
{
if (PropertyChanged != null)
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
#endregion
}
以及关联的 XAML
<Window
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
x:Name="window" x:Class="Testing1.MainWindow">
<Grid>
<Grid HorizontalAlignment="Center" VerticalAlignment="Center" Width=" 300">
<Grid.RowDefinitions>
<RowDefinition/>
<RowDefinition Height="10"/>
<RowDefinition/>
</Grid.RowDefinitions>
<ComboBox x:Name="FirstOne" ItemsSource="{Binding FirstComboValues}" SelectedItem="{Binding FirstSelectedValue, Mode=TwoWay}"/>
<ComboBox x:Name="SecondOne" ItemsSource="{Binding SecondComboValues}" SelectedItem="{Binding SecondSelectedValue, Mode=TwoWay}" Grid.Row="2"/>
</Grid>
</Grid>
</Window>
如您所见，组合框的 SelectedValue 属性以双向模式绑定，因此当组合框的 SelectedValue 属性更改时，它会更改 VM 端的值.在 FirstSelectedValue 属性设置器中调用 UpdateSecondComboValues() 方法来更新第二个组合框的值.
As you can see the SelectedValue properties of combo boxes are binded in TwoWay mode so when SelectedValue property of the combo box changes it changes the value on the VM side. And in FirstSelectedValue property setter UpdateSecondComboValues() method is called to update values for the second combo box.
发生这种情况是因为您混合了 INotifPropertyChanged 和 DependencyObject.您应该选择其中之一.通常，您在 VM 中实现 INotifyPropertyChanged 并且属性设置器中的代码将起作用.
It happens because you mixed both INotifPropertyChanged and DependencyObject. You should choose one of them. Usually you implement INotifyPropertyChanged in your VM and the code in the property setter will work.
但是，如果您从 DependencyObject 继承，则不应在 setter/getter 中编写任何代码.TwoWay 绑定永远不会调用它.它只会在内部调用 GetValue(...).为了能够对 DependencyProperty 更改执行操作，您应该使用属性更改处理程序对其进行不同的声明:
If you inherit from DependencyObject however, you should not write any code in the setter/getter. It will never be called by the TwoWay binding. It will just call GetValue(...) internally. To be able to execute an action on DependencyProperty change you should declare it differently with a property changed handler:
#region BrowserStackDesktopOSSelectedValue
/// <summary>
/// BrowserStackDesktopOSSelectedValue Dependency Property
/// </summary>
public static readonly DependencyProperty BrowserStackDesktopOSSelectedValue Property =
DependencyProperty.Register("BrowserStackDesktopOSSelectedValue ", typeof(string), typeof(YourVM),
new FrameworkPropertyMetadata((string)null,
new PropertyChangedCallback(OnBrowserStackDesktopOSSelectedValue Changed)));
/// <summary>
/// Gets or sets the BrowserStackDesktopOSSelectedValue property. This dependency property
/// indicates ....
/// </summary>
public string BrowserStackDesktopOSSelectedValue
{
get { return (string)GetValue(BrowserStackDesktopOSSelectedValue Property); }
set { SetValue(BrowserStackDesktopOSSelectedValue Property, value); }
}
/// <summary>
/// Handles changes to the BrowserStackDesktopOSSelectedValue property.
/// </summary>
private static void OnBrowserStackDesktopOSSelectedValue Changed(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
YourVM target = (YourVM)d;
string oldBrowserStackDesktopOSSelectedValue = (string)e.OldValue;
string newBrowserStackDesktopOSSelectedValue = target.BrowserStackDesktopOSSelectedValue ;
target.OnBrowserStackDesktopOSSelectedValue Changed(oldBrowserStackDesktopOSSelectedValue , newBrowserStackDesktopOSSelectedValue );
}
/// <summary>
/// Provides derived classes an opportunity to handle changes to the BrowserStackDesktopOSSelectedValue property.
/// </summary>
protected virtual void OnBrowserStackDesktopOSSelectedValue Changed(string oldBrowserStackDesktopOSSelectedValue , string newBrowserStackDesktopOSSelectedValue )
{
//Here write some code to update your second ComboBox content.
AvailableBrowserStackDesktopOSVersions = AvailableBrowserStackDesktopPlatforms.GetOSVersions(BrowserStackDesktopOSSelectedValue);
}
#endregion
顺便说一句，我总是使用 Dr WPF 片段 编写 DP 使其运行速度更快.
By the way I always use Dr WPF snippets to write DPs so it goes much faster.
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