如何确定哪个用户控件正在调用命令

Question

Relative new to MVVM - I realize this is simple question but can't seem to find the answer.

I have 4 grouped radio buttons that when one is selected will show its associated options. I assume these 4 radio buttons should be linked to the same viewmodel command which in this case is called UpdateIndex .

How do I determine which of the radio buttons is calling the UpdateIndex so that I can take appropriate action and show the appropriate options?

Note that my UpdateIndex and UpdateIndexExecute does get called correctly from my radio button command binding, I just don't know how to determine which radio button is calling it. I assume it has to do with CommandParameter - but not sure how to access it from the viewmodel.

An example of my radio button:

<RadioButton
    Content="Option 1"
    GroupName="GroupHeader"
    Command="{Binding UpdateIndex}" />

Code snippet of my command being called from the radio button when clicked...

void UpdateIndexExecute()
{

}

bool CanUpdateIndex()
{
   return true;
}

public ICommand UpdateIndex
{
    get
    {
        return new RelayCommand(UpdateTabIndexExecute, CanUpdateTabIndex);
    }
}

Answer 1

In a true MVVM implementation, you won't know which RadioButton executed the command, because the ViewModel should not have any information about the View. User Controls fall squarely in the category of "things that only exist within the View, not the ViewModel." You should instead pass something meaningful to the ViewModel.

You are correct there are ways to pass information into an ICommand using the "CommandParameter" of a Command Binding. For that, you would use the "generic" form of the RelayCommand ( RelayCommand ) class, where "T" represents the type of object you are passing as a parameter.

If you're just trying to pass an index as a parameter, I imagine it'll look something like this:

<!-- We are passing index "1" as a parameter -->
<RadioButton Content="Option 1"  GroupName="GroupHeader" 
             Command="{Binding UpdateIndex, CommandParameter=1}"/> 

Then in your ViewModel:

void UpdateIndexExecute(int index)
{

}
    
bool CanUpdateIndex(int index)
{
    return true;
}

public ICommand UpdateIndex 
{ 
    get 
    { 
        return new RelayCommand<int>(UpdateTabIndexExecute, CanUpdateTabIndex); 
    } 
}

Answer 2

您可以绑定内容，而不是绑定命令，使用 INotifyPropertyChanged 接口来处理控件所做的更改。