wpf 如何使用 DelegateCommand 将信息从 View 传递到 ViewModel？
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How do I pass the information from View to ViewModel with DelegateCommand?
提问by Edward Tanguay
In my View, I have a button.
在我的视图中，我有一个按钮。
When the user clicks this button, I want to have the ViewModel save the context of the TextBlock in the database.
当用户单击此按钮时，我希望 ViewModel 将 TextBlock 的上下文保存在数据库中。
<StackPanel HorizontalAlignment="Left" VerticalAlignment="Top">
<TextBlock Text="{Binding FirstName}"/>
<TextBox Text="Save this text to the database."/>
<Button Content="Save" Command="{Binding SaveCommand}"/>
</StackPanel>
However, in my DelegateCommand in my ViewModel, the "Save()" method doesn't pass any arguments, so how do I get data from the view at that point?
但是，在我的 ViewModel 中的 DelegateCommand 中，“Save()”方法不传递任何参数，那么此时如何从视图中获取数据？
#region DelegateCommand: Save
private DelegateCommand saveCommand;
public ICommand SaveCommand
{
get
{
if (saveCommand == null)
{
saveCommand = new DelegateCommand(Save, CanSave);
}
return saveCommand;
}
}
private void Save()
{
TextBox textBox = ......how do I get the value of the view's textbox from here?....
}
private bool CanSave()
{
return true;
}
#endregion
回答by Matt Hamilton
Check out this MSDN article by Josh Smith. In it, he shows a variation of DelegateCommand that he calls RelayCommand, and the Execute and CanExecute delegates on RelayCommand accept a single parameter of type object.
查看Josh Smith 撰写的这篇 MSDN 文章。在其中，他展示了他称为 RelayCommand 的 DelegateCommand 的变体，并且 RelayCommand 上的 Execute 和 CanExecute 委托接受类型为 object 的单个参数。
Using RelayCommand you can pass information to the delegates via a CommandParameter:
使用 RelayCommand 您可以通过 CommandParameter 将信息传递给代表：
<Button Command="{Binding SaveCommand}"
CommandParameter="{Binding SelectedItem,Element=listBox1}" />
Update
更新
Looking at this article, it appears that there is a generic version of DelegateCommand which accepts a parameter in a similar way. You might want to try changing your SaveCommand to a DelegateCommand<MyObject>and change your Save and CanSave methods so that they take a MyObject parameter.
查看这篇文章，似乎有一个通用版本的 DelegateCommand 以类似的方式接受参数。您可能想尝试将 SaveCommandDelegateCommand<MyObject>更改为 a并更改 Save 和 CanSave 方法，以便它们采用 MyObject 参数。
回答by Matt Hamilton
here is the elegant way.
这是优雅的方式。
Give a name to your textbox, then bind the CommandParameter in the button to it's Text property:
为您的文本框命名，然后将按钮中的 CommandParameter 绑定到它的 Text 属性：
<StackPanel HorizontalAlignment="Left" VerticalAlignment="Top">
<TextBlock Text="{Binding FirstName}"/>
<TextBox x:Name="ParameterText" Text="Save this text to the database."/>
<Button Content="Save" Command="{Binding SaveCommand}"
CommandParameter="{Binding Text, ElementName=ParameterText}"/>
</StackPanel>
回答by Carlos
In your VM:
在您的虚拟机中：
private DelegateCommand<string> _saveCmd = new DelegateCommand<string>(Save);
public ICommand SaveCmd{ get{ return _saveCmd } }
public void Save(string s) {...}
In you View, use CommandParameter like Matt's example.
在您的视图中，像 Matt 的示例一样使用 CommandParameter。
回答by Jeffrey Knight
You're asking about passing data via the button Command.
您正在询问通过按钮命令传递数据。
What you actually want, I think, is to bindyour Textbox's text to a public propertyin your ViewModel:
我认为您真正想要的是将您的文本框的文本绑定到您的 ViewModel 中的公共属性：
<!-- View: TextBox's text is bound to the FirstName property in your ViewModel -->
<TextBox Text="{Binding Path=FirstName}" />
<Button Command="{Binding SaveCommand}"/>
<!-- ViewModel: Expose a property for the TextBox to bind to -->
public string FirstName{ get; set; }
...
private void Save()
{
//textBox's text is bound to --> this.FirstName;
}
回答by ml_black
I'm not allowed to make comments yet, I guess. I'm responding to Carlos' suggestion because I tried it out. While it's a great idea, DelegateCommand would need to be modified in some way because otherwise you'll get this error: A field initializer cannot reference the non-static field, method, or property 'MyViewModel.Save(string)'.
我还不能发表评论，我猜。我正在回应卡洛斯的建议，因为我已经尝试过了。虽然这是一个好主意，但需要以某种方式修改 DelegateCommand，否则您将收到此错误：字段初始值设定项无法引用非静态字段、方法或属性“MyViewModel.Save(string)”。
