Message List View Model

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MessageListViewModel works with MessageListView and uses StreamChatAndroidOffline library to communicate with Stream API.

The view model exposes two LiveData objects, as well as two values:

• mode - distincts if the view is in thread mode, can be one of:

  • Thread

  • Normal

• state - can be one of:

  • Loading

  • Result

  • NavigateUp

• currentUser

• channel

You can inform the view model about new events using onEvent method. Currently, MessageListViewModel supports the following events:

• BaskButtonPressed

• EndRegionReached

• LastMessageRead

• ThreadModeEntered

• DeleteMessage

• FlagMessage

• GiphyActionSelected

• RetryMessage

Creating Message List View ModelCopied!

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MessageListViewModel can be instantiated using ChannelViewModelFactory:

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ChannelViewModelFactory factory = new ChannelViewModelFactory(channel.getCid()); 
MessageListViewModel viewModel = new ViewModelProvider(this, factory) 
        .get(MessageListViewModel.class);

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private val viewModel: MessageListViewModel by viewModels { 
    ChannelViewModelFactory(channel.cid) 
}

Binding with MessageListViewCopied!

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MessageListViewModel can be bound with MessageListView using MessageListViewModelBinding:

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MessageListViewModelBinding.bind(viewModel, messageListView, lifecycle);

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viewModel.bindView(messageListView, viewLifecycleOwner)C

Calling bind method results in:

• Initializing view with the channel and current user

• Displaying new messages

• Setting:

  • EndRegionReachedHandler

  • LastMessageReadHandler

  • OnMessageDeleteHandler

  • OnStartThreadHandler

  • OnMessageFlagHandler

  • OnSendGiphyHandler

  • OnMessageRetryHandler

Handling back button pressCopied!

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MessageListViewModel contains a mechanism for handling back button behaviour when you're in a thread. If you want to use it, you need to override Activitiy's back button behaviour:

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getOnBackPressedDispatcher().addCallback(lifecycleOwner, new OnBackPressedCallback(true) { 
    @Override 
    public void handleOnBackPressed() { 
        messageListViewModel.onEvent(MessageListViewModel.Event.BackButtonPressed.INSTANCE); 
    } 
});

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onBackPressedDispatcher.addCallback( 
    lifecycleOwner, 
    object : OnBackPressedCallback(true) { 
        override fun handleOnBackPressed() { 
            messageListViewModel.onEvent(MessageListViewModel.Event.BackButtonPressed) 
        } 
    } 
)

The view model will exit the thread if needed and emit MessageListViewModel.State.NavigateUp if user isn't inside a thread. You need to handle this state by yourself - for example, by finishing the current Activity:

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messageListViewModel.getState().observe(lifecycleOwner, state -> { 
    if (state instanceof MessageListViewModel.State.NavigateUp) { 
        finish(); 
    } 
});

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messageListViewModel.state.observe(lifecycleOwner) { 
    when (it) { 
        is MessageListViewModel.State.NavigateUp -> finish() 
        else -> Unit 
    } 
}