CODEWITHSUNDEEP
androidandroid-architecture-components
kazume
kazume

Reputation: 1373

How to make EditText observe a ViewModel's LiveData and forward user input to the ViewModel without using data binding

I'm trying to come up with a way to have an EditText update the data of a ViewModel and simultaneously observe that data for any changes (e.g. changes brought about by manipulating the DB). Is there a way to do this without using the data binding library?

The main problem I'm facing while simply using MutableLiveData is the following:

when the user enters text in the EditText, a TextWatcher pokes the ViewModel to update its data, which in turn will set the new text to the MutableLiveData object. Because the EditText is observing the LiveData, the onChange is triggered and sets the text of the EditText accordingly, which in turn will trigger the TextWatcher again creating an infinite loop.

Upvotes: 24

Views: 15960

Answers (4)

Mikhail
Mikhail

Reputation: 3305

In opposition to Carson Holzheimer solution I moved the validation to the UI layer (e.g. Activity or Fragment):

viewModel.textValue.observe(this, { text ->
    if (myEditText.text.toString() != text) {
        myEditText.setText(text)
    }
})

This helped me to avoid an infinite loop.

Upvotes: 1

Jeff Padgett
Jeff Padgett

Reputation: 2529

I think you can also use LiveData.distinctUntilChanged(), which will only emit data when new value is set.

Upvotes: 0

Reyhane Farshbaf
Reyhane Farshbaf

Reputation: 543

May be a little late, but hope useful for somebody. I had this problem and what I did was consider a string member for the viewmodel class to maintain last value of editText. Everytime it would be to return livedata, It checks it first is there difference between new edittext input(getData() parameter) and its past value (saved in myVariable):

  public class MyViewModel extends ViewModel {
  private MutableLiveData<DataType> data;
  private String myVariable; //maintainer variable

  public LiveData<DataType> getData(String input){
    if(data == null || !myVariable.equals(input)){
      myVariable = input;
      data = new MutableLiveData<>();
      loadData(data, input);
    }
    return data;
  }

and in your owner(eg. Activity) observe data changes:

myViewModel = ViewModelProviders.of(this).get(MyViewModel.class);    
editText.addTextChangedListener(new TextWatcher() {
  @Override
  public void beforeTextChanged(CharSequence s, int start, int count, int after) {    
  }

  @Override
  public void onTextChanged(CharSequence s, int start, int before, int count) {
     myViewModel.getData(s).observe(this, new Observer<DataType>() {
      @Override
      public void onChanged(<DataType> data) {
        //do everything you want like update UI by data
      }
    });
  }

  @Override
  public void afterTextChanged(Editable s) {         
  }
});

Upvotes: 2

Carson Holzheimer
Carson Holzheimer

Reputation: 2963

I also ran into this problem since I don't like the databinding library. I did as @kAliert said, but in my ViewModel to keep the logic there. I just added a simple catch on the function that receives my text changes events in the ViewModel. It works well.

fun editTextChanged(newText: String) {
    if (newText == textLiveData.value) {
        return
    }
}

Upvotes: 7

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