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[英]Changing LiveData in Activity doesn't notify observer in child Fragment
[英]Why LiveData observer is not called? (Android, Fragment)
即使 LiveData 值发生变化,我的观察者也不会被调用。 我究竟做错了什么?
观察者和 model 在片段中初始化。 按钮用于通过方法(计算后跟设置方法)更改 model 中的值。 但是,观察者不会记录 model 值的任何更改。
分段
public class PlayerFragment extends Fragment {
private PlayerViewModel mViewModel;
private ImageButton volumeUp, volumeDown;
public static PlayerFragment newInstance() {
return new PlayerFragment();
}
public void onViewCreated(@NonNull View view, Bundle savedInstanceState) {
super.onViewCreated(view, savedInstanceState);
volumeDown = getView().findViewById(R.id.btn_player_volume_down);
volumeDown.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
mViewModel.volumeDown();
}
});
volumeUp = getView().findViewById(R.id.btn_player_volume_up);
volumeUp.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
mViewModel.volumeUp();
}
});
final Observer<Integer> volumeObserver = new Observer<Integer>() {
@Override
public void onChanged(Integer volValue) {
SeekBar volume = getView().findViewById(R.id.player_volumeBar);
volume.setProgress( volValue );
}
};
mViewModel.getVolume().observe(getViewLifecycleOwner(), volumeObserver);
}
@Override
public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
mViewModel = new ViewModelProvider(this).get(PlayerViewModel.class);
return inflater.inflate(R.layout.fragment_player, container, false);
}
@Override
public void onResume() {
super.onResume();
((MainActivity) getActivity()).getSupportActionBar().setTitle( getString(R.string.fragment_player_title) );
mViewModel.fetchPlayerData();
}
}
视图模型
public class PlayerViewModel extends ViewModel {
private MutableLiveData<Integer> volume;
public PlayerViewModel(){
volume = new MutableLiveData<Integer>();
fetchPlayerData();
}
public void fetchPlayerData(){
volume = new MutableLiveData<Integer>(1);
}
public void volumeUp() {
volume.postValue( volume.getValue() + 5 );
Log.i( "volumeUp", "Set new volume:" + volume.getValue().toString() );
}
public void volumeDown() {
volume.postValue( volume.getValue() - 5 );
Log.i( "volumeDown", "Set new volume:" + volume.getValue().toString() );
}
}
方法fetchPlayerData()
为volume
分配一个新的 MutableLiveData,这会导致在旧数据上注册的观察者丢失。 在注册观察者之后,它再次在onResume()
中被调用。
您可以将fetchPlayerData()
更改为如下所示:
volume.postValue(1)
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