Welcome to OGeek Q&A Community for programmer and developer-Open, Learning and Share
Welcome To Ask or Share your Answers For Others

Categories

0 votes
385 views
in Technique[技术] by (71.8m points)

c# - How to use CanExecute with Mvvmcross

I have a Button

<Button 
      android:id="@+id/ButtonConnect"
      android:layout_width="match_parent"
      android:layout_height="wrap_content"
      android:text="Disconnect"
      local:MvxBind="{'Click':{'Path':'DisconnectCommand'}}" />

And I have a Command for it

public IMvxCommand DisconnectCommand
{
    get
    {
        return new MvxRelayCommand(this.GetService<IConnectionService>().Disconnect);
    }
}

Then I want to enable/disable the DisconnectCommand using

DisconnectCommand.CanExecute(this.GetService<IConnectionService>().UsbConnected);

But thats clearly wrong (It is not working), I put the check in as a a parameter, but normally I would do

DisconnectCommand.CanExecute = someBool;

But there is no property to set, so how to go about this?

See Question&Answers more detail:os

与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…
Welcome To Ask or Share your Answers For Others

1 Reply

0 votes
by (71.8m points)

To work out how to use CanExecute, take a look at Silverlight or WPF - there's lots of blogs out there which talk about how to use ICommand - e.g. http://weblogs.asp.net/nmarun/archive/2009/12/02/using-icommand-silverlight-4.aspx or http://blog.galasoft.ch/archive/2009/09/26/using-relaycommands-in-silverlight-and-wpf.aspx

An example would be something like:

private MvxRelayCommand _disconnectCommand;
public IMvxCommand DisconnectCommand
{
    get
    {
        if (_disconnectCommand == null)
            _disconnectCommand = new MvxRelayCommand(this.GetService<IConnectionService>().Disconnect, item => this.IsItemConnected(item));
        return _disconnectCommand;
    }
}

private void SomeServiceNotificationHandler()
{
    _disconnectCommand.RaisePropertyChanged();
}

private bool IsItemConnected(object thing)
{
    return /* your code */;
}

There is one small problem though....

CanExecute isn't really fully implemented across all the MvxBindings across all platforms... It will work for some of them, but for some of them it won't - and I don't really know which ones at present! If you come across issues, then please let me know (via GitHub issues) and they will get fixed...


Personally... I don't tend to use CanExecute - I tend instead to use a separate Boolean property which I then bind to whatever property is available on the control - e.g. most controls have something like Enabled, IsEnabled, Disabled, IsDisabled, etc.

I generally find it easier (and more readable) to set the Boolean property rather than to call RaiseCanExecuteChanged

e.g. I'd use something like:

<Button 
  android:id="@+id/ButtonConnect"
  android:layout_width="match_parent"
  android:layout_height="wrap_content"
  android:text="Disconnect"
  local:MvxBind="{'Click':{'Path':'DisconnectCommand'},'Enabled':{'Path':'UsbConnected'}}" />

You can definitely argue that the CanExecute approach has advantages - because it keeps the Command logic all in one object, and because it can be used to prevent Execute calls happening within the RelayCommand. That's why I'm happy to try to fix CanExecute bugs in mvvmcross bindings as we find them.


与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…
OGeek|极客中国-欢迎来到极客的世界,一个免费开放的程序员编程交流平台!开放,进步,分享!让技术改变生活,让极客改变未来! Welcome to OGeek Q&A Community for programmer and developer-Open, Learning and Share
Click Here to Ask a Question

...