[WP7][MVVM Light 工具包] 使用 mvvm-light 工具包时在绑定之前过早引发按钮命令
我在 Windows Phone 7 应用程序中使用 mvvm-light 工具包。
我的观点是：
<TextBox Height="78" HorizontalAlignment="Left" Margin="108,33,0,0" VerticalAlignment="Top" Width="313" Text="{Binding MyValue, Mode=TwoWay}" />
<Button Content="Go" Height="78" HorizontalAlignment="Left" Margin="127,252,0,0" Name="button1" VerticalAlignment="Top" Width="213" cmd:ButtonBaseExtensions.Command="{Binding DoCommand}" />
我的视图模型是：
public class MainPageViewModel : ViewModelBase
{
public ICommand DoCommand { get; internal set; }
public MainPageViewModel()
{
DoCommand = new RelayCommand(() =>
{
DoSomethingWith(MyValue);
}, () => true);
}
private const string MyValuePropertyName = "MyValue";
private string _myValue;
public string MyValue
{
get { return _myValue; }
set
{
if (_myValue == value)
return;
_myValue = value;
RaisePropertyChanged(MyValuePropertyName);
}
}
}
在模拟器中，当我在文本框中输入值并单击按钮时，我可以看到我首先进入中继命令 lambda 表达式并带有断点 我看到 MyValue 为空。然后，到达 MyValue setter 中的断点，并且正确的值进入 MyValue。
我做错了什么？当然，我希望可以在 RelayCommand 之前到达设置器...
提前感谢您的帮助。
I'm using the mvvm-light toolkit in my windows phone 7 application.
I have in my view :
<TextBox Height="78" HorizontalAlignment="Left" Margin="108,33,0,0" VerticalAlignment="Top" Width="313" Text="{Binding MyValue, Mode=TwoWay}" />
<Button Content="Go" Height="78" HorizontalAlignment="Left" Margin="127,252,0,0" Name="button1" VerticalAlignment="Top" Width="213" cmd:ButtonBaseExtensions.Command="{Binding DoCommand}" />
My view model is :
public class MainPageViewModel : ViewModelBase
{
public ICommand DoCommand { get; internal set; }
public MainPageViewModel()
{
DoCommand = new RelayCommand(() =>
{
DoSomethingWith(MyValue);
}, () => true);
}
private const string MyValuePropertyName = "MyValue";
private string _myValue;
public string MyValue
{
get { return _myValue; }
set
{
if (_myValue == value)
return;
_myValue = value;
RaisePropertyChanged(MyValuePropertyName);
}
}
}
In the emulator, when I type value in the textbox, and I click the button, I can see that I'm going first in the relaycommand lambda expression and with a breakpoint
I see that MyValue is null. Then, the breakpoint in the setter of MyValue is reached, and the correct value goes in MyValue.
What am I doing wrong ? Of course, I would like that the setter can be reached before the RelayCommand...
Thanks in advance for any help.
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您可能遇到了 TextChanged 事件的 TextBox DataBinding 问题。这是 Silverlight 3 中公认的问题，查看讨论此问题的帖子以及解决方法。一个巧妙的解决方案可能是使用 这篇文章。
HTH，indyfromoz
It is possible that you have hit the TextBox DataBinding issue with the TextChanged event. This is a recognized problem in Silverlight 3, see this thread discussing this issue and the workaround. A neat solution is perhaps to use behaviors as discussed in this article.
HTH, indyfromoz