LiveDataBus

解决粘连问题;反射找到mLastVersion,赋值为 mVersion; mLastVersion hook起点在mObservers

public static class xxMutableLiveData<T> extends MutableLiveData<T>{
    @override
    public void observer(@NonNull LifecycleOwner owner,@NonNull Observer<? super T>  observer){
      super.observer(owner, observer);
      hook(observer);
  }
}

private void hook(Observer<? super T> observer){
        try{
            Class<LiveData> liveDataClass = LiveData.class;
            Field mObserversField = liveDataClass.getDeclaredField("mObservers");
            mObserversField.setAccessible(true);
            Object observersObject = mObserversField.get(this);
            Class<?> observersClass = observersObject.getClass();
            Method get = observersClass.getDeclaredMethod("get",Object.class);
            get.setAccessible(true);
            Object invokeEntry = get.invoke(observersObject, observer);
            Object observerWrapper = null;
            if(invokeEntry!=null&&invokeEntry instanceof Map.Entry){
                observerWrapper = ((Map.Entry)invokeEntry).getValue();
            }
            Class<?> superClass = observerWrapper.getClass().getSuperclass();
            Field mLastVersion = superClass.getDeclaredField("mLastVersion");
            mLastVersion.setAccessible(true);
            Field mVersion = liveDataClass.getDeclaredField("mVersion");
            mVersion.setAccessible(true);
            Object mVersionEntry = mVersion.get(this);
            mLastVersion.set(observerWrapper,mVersionEntry);
        }catch(Exception e){
            
        }
    }

DataBinding

使用

public class xxVM extends  BaseObservable{
  private String xx1;
  private String xx2;

  @Bindable
  public String getXx1(){
    return xx1;
  }

  public void setXx1(String xx1){
    this.xx1 = xx1;
    notifyPropertyChanged(BR.xx1);
  }

  @Bindable
  public String getXx2(){
    return xx2;
  }

  public void setXx2(String xx2){
    this.xx2 = xx2;
    notifyPropertyChanged(BR.xx2);
  }

}

<layout>
  <data>
      <variable
        name = "xxVM"
        type = "com.xx.xx.xxVM"
      />
  </data>
</layout>

android:text = "{xxVM.xx1}"

...XxActivity extends AppCompatActivity...
XxActivityBinding xxBinding;
XxVM xxVM;
  ...onCreate...{
    xxBinding= DataBindingUtil.setContentView(this,R.layout.xx);
    xxBinding.setXxVM(xxVM);
  }

  //赋值
  ...
  xxVM.setXx1("xyz");//可以自动更新到界面上
  ...
...

原理

1. xxBinding= DataBindingUtil.setC...：apt生成的代码里面 xml会被分离成两部分，并且加了tag
2. xxBinding.setXxVM(xxVM)：从apt代码中找，跳转到ViewDataBinding中 mLocalFieldObservers 存储了xml中的各个节点的数据，比如有3个节点就会处理3个监听
3. xxActivityBindingImpl 的executeBindings()来处理设置数据到界面上
4. BR 用来处理和界面上的绑定，这里用到了位的或运算提升速度