正在将ObservableDictionary绑定到组合框(WPF)

Question

我本以为这个问题已经得到了答案，但我没有找到。我有一个简单的类：

public class BinanceEndpoint : ObservableObject
{
private string baseAddress;
private string socketBaseAddress;
public string BaseAddress
{
get { return baseAddress; }
set { baseAddress = value; RaisePropertyChangedEvent(nameof(BaseAddress)); }
}
public string SocketBaseAddress
{
get { return socketBaseAddress; }
set { socketBaseAddress = value; RaisePropertyChangedEvent(nameof(SocketBaseAddress)); }
}
}

然后，我用这个类的对象填充ObservableDictionary：

private MainViewModel()
{
private BinanceEndpoint apiEndPoint;
private ObservableDictionary<string, BinanceEndpoint> endPoints = new ObservableDictionary<string, BinanceEndpoint>();

endPoints.Add("Binance.com", new BinanceEndpoint() { BaseAddress = "https://api.binance.com", SocketBaseAddress = "wss://stream.binance.com:9443", });
endPoints.Add("Binance.us", new BinanceEndpoint() { BaseAddress = 

"https://api.binance.us", SocketBaseAddress = "wss://stream.binance.us:9443", });
endPoints.Add("Testnet", new BinanceEndpoint() { BaseAddress = "https://testnet.binance.vision", SocketBaseAddress = "wss://testnet.binance.vision", });
}
[JsonIgnore]
public ObservableDictionary<string,BinanceEndpoint> EndPoints
{
get { return endPoints; }
set { endPoints = value; RaisePropertyChangedEvent(nameof(EndPoints)); }
}
public BinanceEndpoint APIEndPoint
{
get { return apiEndPoint; }
set { apiEndPoint = value; RaisePropertyChangedEvent(nameof(APIEndPoint)); }
}
}

然后我尝试使用ObservableDictionary来填充ComboBox。

<ComboBox Grid.Column="1" ItemsSource="{Binding EndPoints}" DisplayMemberPath="Key" SelectedValuePath="Value" SelectedValue="{Binding Path=APIEndPoint, Mode=TwoWay}"/>

我遇到的问题是SelectedValue在加载时不会更新组合框的值。我做错了什么？

Answer 1

首先应该避免绑定到Dictionary。.NET库中没有ObservableDictionary是有原因的——自2002年发布以来。我想我们同意这并不是因为MS开发人员这么多年后不知道如何实现这样一个字典。

您的SelectedValuePath和SelectedValue使用错误。SelectedValue返回SelectedValuePath所指向的属性的值。SelectedValuePath提供了SelectedItem上的属性路径
当您主动设置SelectedValue时，控件将尝试查找并选择SelectedValuePath指定的项目属性与SelectedValue值匹配的项目。

当SelectedItem返回所选项目(实例)时，则SelectedValue返回使用SelectedValuePath指定的该SelectedItem上的属性的值。

例如：我们绑定到一个Dictionary<string, BinanceEndpoint>。要显示Dictionary的Key，我们指定DisplayMemberPath(作为DataTemplate的替代方案)
SelectedItem将保存KeyValuePair<string, BinanceEndpoint>
要使ComboBox.SelectedValue返回所选项目的SocketBaseAddress值，我们必须将SelectedValuePath设置为"Value.SocketBaseAddress":

<ComboBox x:Name="ComboBox" 
ItemsSource="{Binding EndPoints}" 
DisplayMemberPath="Key" 
SelectedValuePath="Value.SocketBaseAddress" />
<!-- Display the selected item's SocketBaseAddress value -->
<TextBlock text="{Binding ElementName=ComboBox, Path=SelectedValue}" />

如果希望SelectedValue返回BinanceEndpoint实例，则将SelectedValuePath设置为"Value":

<ComboBox x:Name="ComboBox" 
ItemsSource="{Binding EndPoints}" 
DisplayMemberPath="Key" 
SelectedValuePath="Value" />
<!-- Display the selected item's 'SocketBaseAddress' value -->
<TextBlock text="{Binding ElementName=ComboBox, Path=SelectedValue.SocketBaseAddress}" />