@Bindable
protected ItemClickPresenter mPresenter;
protected PartialListItemBinding(DataBindingComponent _bindingComponent, View _root,
int _localFieldCount, ImageView imageView) {
//调用父类的构造方法
super(_bindingComponent, _root, _localFieldCount);
this.imageView = imageView;
}
//…
}
调用了父类ViewDataBinding的构造方法，并传入了三个参数，这里看第三个参数_localFieldCount，它代表xml中存在几个ObservableField形式的数据，继续追踪.
protected ViewDataBinding(DataBindingComponent bindingComponent, View root, int localFieldCount) {
this.mBindingComponent = bindingComponent;
//考点1
this.mLocalFieldObservers = new ViewDataBinding.WeakListener[localFieldCount];
this.mRoot = root;
if (Looper.myLooper() == null) {
throw new IllegalStateException(“Dat
aBinding must be created in view’s UI Thread”);
} else {
if (USE_CHOREOGRAPHER) {
//考点2
this.mChoreographer = Choreographer.getInstance();
this.mframeCallback = new frameCallback() {
public void doframe(long frameTimeNanos) {
ViewDataBinding.this.mRebindRunnable.run();
}
};
} else {
this.mframeCallback = null;
this.mUIThreadHandler = new Handler(Looper.myLooper());
}
}
}
通过观察，发现其根据localFieldCount初始化了一个WeakListener数组，名为mLocalFieldObservers。另一个重点是初始化了一个mframeCallback，在回调中执行了mRebindRunnable.run。
当生成的PartialListItemBindingImpl对象调用executeBindings方法时，通过updateRegistration会对mLocalFieldObservers数组中的内容进行赋值。
随之生成的是相应的WeakPropertyListener，来看看它的定义。
private static class WeakPropertyListener extends Observable.OnPropertyChangedCallback
implements ObservableReference {
final WeakListener mListener;
public WeakPropertyListener(ViewDataBinding binder, int localFieldId) {
mListener = new WeakListener(binder, localFieldId, this);
}
//…
@Override
public void onPropertyChanged(Observable sender, int propertyId) {
ViewDataBinding binder = mListener.getBinder();
if (binder == null) {
return;
}
Observable obj = mListener.getTarget();
if (obj != sender) {
return; // notification from the wrong object?
}
//划重点
binder.handleFieldChange(mListener.mLocalFieldId, sender, propertyId);
}
}
当ObservableField的值有改变的时候，onPropertyChanged会被调用，然后就会回调binder(即binding对象)的handleFieldChange方法，继续观察。
private void handleFieldChange(int mLocalFieldId, Object object, int fieldId) {
if (!this.mInLiveDataRegisterObserver) {
boolean result = this.onFieldChange(mLocalFieldId, object, fieldId);
if (result) {
this.requestRebind();
}
}
}
如果值有改变 ，result为true，接着requestRebind方法被执行。
protected void requestRebind() {
if (this.mContainingBinding != null) {
this.mContainingBinding.requestRebind();
} else {
synchronized(this) {
if (this.mPendingRebind) {
return;
}
this.mPendingRebind = true;
}
if (this.mLifecycleOwner != null) {
State state = this.mLifecycleOwner.getLifecycle().getCurrentState();
if (!state.isAtLeast(State.STARTED)) {
return;
}
}
//划重点
if (USE_CHOREOGRAPHER) { // SDK_INT >= 16
this.mChoreographer.postframeCallback(this.mframeCallback);
} else {
this.mUIThreadHandler.post(this.mRebindRunnable);
}
}
}
在上述代码最后，可以看到sdk版本16以上会执行
this.mChoreographer.postframeCallback(this.mframeCallback);，16以下则是通过Handler。
关于postframeCallBack，给的注释是Posts a frame callback to run on the next frame.，简单理解就是发生在下一帧即16ms之后的回调。
关于Choreographer，推荐阅读** Choreographer 解析**
https://www.jianshu.com/p/dd32ec35db1d
但不管如何，最终都是调用mRebindRunnable.run，来看看对它的定义。
private final Runnable mRebindRunnable = new Runnable() {
@Override
public void run() {
synchronized (this) {
mPendingRebind = false;
}
processReferenceQueue();
if (VERSION.SDK_INT >= VERSION_CODES.KITKAT) {
// Nested so that we don’t get a lint warning in IntelliJ
if (!mRoot.isAttachedToWindow()) {
// Don’t execute the pending bindings until the View
// is attached again.
mRoot.removeonAttachStateChangeListener(ROOT_REATTACHED_LISTENER);
mRoot.addonAttachStateChangeListener(ROOT_REATTACHED_LISTENER);
return;
}
}
//划重点
sted so that we don’t get a lint warning in IntelliJ
if (!mRoot.isAttachedToWindow()) {
// Don’t execute the pending bindings until the View
// is attached again.
mRoot.removeonAttachStateChangeListener(ROOT_REATTACHED_LISTENER);
mRoot.addonAttachStateChangeListener(ROOT_REATTACHED_LISTENER);
return;
}
}
//划重点
