【android学习】Jetpack：LiveData共享数据

简介

前面讲解了LiveData的简单使用Jetpack：LiveData的简单使用，这里主要讲解livedata的数据共享

我们这里使用LiveData进行两个fragment之间通信，达到如下效果

先看ViewModel类

public class NameViewModel extends ViewModel {

    //liveData通常和viewModel一起使用
    private  MutableLiveData<String> mCurrentName;

    public MutableLiveData<String> getmCurrentName() {
        if (mCurrentName == null) {
            mCurrentName = new MutableLiveData<String>();
        }
        return mCurrentName;
    }

    //如果需要可以在这里释放资源
    @Override
    protected void onCleared() {
        super.onCleared();
    }
}

发送端的fragment

这里点击发送按钮，给NameViewModel 中发送edittext中填入的值

public class FragmentOne extends Fragment {

    private EditText edContent;
    private Button btnSend;
    NameViewModel model;
    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.fragment_one, container, false);
        edContent = view.findViewById(R.id.et_content);
        btnSend = view.findViewById(R.id.btn_send);

        //获取viewModel
        model = ViewModelProviders.of(getActivity()).get(NameViewModel.class);
        btnSend.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                //获取到liveData后设置liveData的值
                model.getmCurrentName().setValue(edContent.getText().toString());
            }
        });
        return view;
    }

}

接收端fragment

这里通过对NameViewModel 的监听，实现对FragmentOne中的edittext值变化的监听

public class FragmentTwo extends Fragment {


    private TextView textName;
    private NameViewModel model;

    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.fragment_two, container, false);
        textName = view.findViewById(R.id.tv_text);

        //获取viewModel
        model = ViewModelProviders.of(getActivity()).get(NameViewModel.class);
        //监听值的变化
        //model.getmCurrentName().observeForever();可以在任何时候得到数据
        model.getmCurrentName().observe(getActivity(), new Observer<String>() {
            @Override
            public void onChanged(@Nullable String s) {
                //更新UI
                textName.setText(s);
            }
        });
        return view;
    }

}

 

我们再看一下activity之间的传值

我们点击第一个activity跳转到第二个activity，在第二个activity中，输入值，设置给MutableLiveData，点击返回，在第一个activity中，监听第二个activity转过来的值

因为ViewModel是个activity生命周期相匹配的，所以我们需要修改一下MutableLiveData为static

    private static MutableLiveData<String> mCurrentName;

监听值activity

public class SecondActivity extends AppCompatActivity implements View.OnClickListener {

    private TextView mTextTv;
    private NameViewModel model;
    private Button mButton;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_second);
        initView();
        //获取viewModel
        model = ViewModelProviders.of(this).get(NameViewModel.class);
        //监听值的变化
        //model.getmCurrentName().observeForever();可以在任何时候得到数据
        model.getmCurrentName().observe(this, new Observer<String>() {
            @Override
            public void onChanged(@Nullable String s) {
                //更新UI
                mTextTv.setText(s);
            }
        });
    }

    private void initView() {
        mTextTv = (TextView) findViewById(R.id.tv_text);
        mButton = (Button) findViewById(R.id.button);
        mButton.setOnClickListener(this);
    }

    @Override
    public void onClick(View v) {
        switch (v.getId()) {
            case R.id.button:
                // TODO 19/10/12
                startActivity(new Intent(this,FirstActivity.class));
                break;
            default:
                break;
        }
    }
}

设置值的activity

public class FirstActivity extends AppCompatActivity implements View.OnClickListener {

    private EditText mContentEt;
    private Button mSendBtn;
    private NameViewModel model;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.fragment_one);
        initView();
        //获取viewModel
        model = ViewModelProviders.of(this).get(NameViewModel.class);
    }

    private void initView() {
        mContentEt = (EditText) findViewById(R.id.et_content);
        mSendBtn = (Button) findViewById(R.id.btn_send);
        mSendBtn.setOnClickListener(this);
    }

    @Override
    public void onClick(View v) {
        switch (v.getId()) {
            case R.id.btn_send:
                //获取到liveData后设置liveData的值
                model.getmCurrentName().setValue(mContentEt.getText().toString());
                break;
            default:
                break;
        }
    }
}

这样，就可以避免使用intent 或者startActivityForResult传值，就可以达到数据传递共享