Activity在inflate layout时，通过DataBindingUtil来生成绑定，从代码看，是遍历contentView得到View数组对象，然后通过数据绑定library生成对应的Binding类，含Views、变量、listeners等。生成类位于
build/intermediates/classes/debug/…package…/databinding/xxx.Java 下，具体如何生成这里暂不作深入。
绑定过程
- 首先，会在父类（ViewDataBinding）中实例化回调或Handler，用于之后的绑定操作；
private static final boolean USE_CHOREOGRAPHER = SDK_INT >= 16;
if (USE_CHOREOGRAPHER) { mChoreographer = Choreographer.getInstance(); mFrameCallback = new Choreographer.FrameCallback() { @Override public void doFrame(long frameTimeNanos) { mRebindRunnable.run(); } };} else { mFrameCallback = null; mUIThreadHandler = new Handler(Looper.myLooper());}
- 接着，通过调用 mapBindings(…) 遍历布局以获得包含bound、includes、ID Views的数组对象，再依次赋给对应View
final Object[] bindings = mapBindings(bindingComponent, root, 3, sIncludes, sViewsWithIds);this.mboundView0 = (Android.widget.LinearLayout) bindings[0];this.mboundView0.setTag(null);
- 然后，调用 invalidateAll() -> requestRebind() -> … -> mRebindRunnable.run() – 执行 Runnable
// 用于动态重新绑定 Viewsprivate final Runnable mRebindRunnable = new Runnable() { @Override public void run() { synchronized (this) { mPendingRebind = false; } ..... executePendingBindings(); }};
- 最后，通过该Runnable会执行到 executePendingBindings() -> … -> executeBindings()，在这里会执行绑定相关操作。
@Overrideprotected void executeBindings() { long dirtyFlags = 0; synchronized(this) { dirtyFlags = mDirtyFlags; // mDirtyFlags 变量更新的标志 mDirtyFlags = 0; } .....}
设置变量(数据对象)
普通 Java bean 对象
- 首先，通过mDirtyFlags标识变量(所有变量共用)
synchronized(this) { mDirtyFlags |= 0x1L;}
- 然后，调用 notifyPropertyChanged(…) 来通知更新（若有回调）
public void notifyPropertyChanged(int fieldId) { if (mCallbacks != null) { mCallbacks.notifyCallbacks(this, fieldId, null); }}
- 最后，调用 requestRebind() -> … -> executeBindings() 再次执行绑定操作，将数据更新到Views上
@Overrideprotected void executeBindings() { long dirtyFlags = 0; synchronized(this) { dirtyFlags = mDirtyFlags; mDirtyFlags = 0; } .....}
Observable 对象
- 在设置变量时，会先调用 updateRegistration(..) 注册一个Observable对象的监听
public void setContact(com.connorlin.databinding.model.ObservableContact contact) { updateRegistration(0, contact); this.mContact = contact; synchronized(this) { mDirtyFlags |= 0x1L; } notifyPropertyChanged(BR.contact); super.requestRebind();}
- 其他步骤同普通 Java bean 对象
ObservableFields 对象
- 前期步骤同普通 Java Bean 对象
- 与 Observable 对象不同的是，Observable对象的监听是在 executeBindings() 中注册的
@Overrideprotected void executeBindings() { long dirtyFlags = 0; synchronized(this) { dirtyFlags = mDirtyFlags; mDirtyFlags = 0; } ... if ((dirtyFlags & 0xfL) != 0) { if ((dirtyFlags & 0xdL) != 0) { if (contact != null) { // read contact.mName mNameContact = contact.mName; } updateRegistration(0, mNameContact);
if (mNameContact != null) { // read contact.mName.get() mNameContact1 = mNameContact.get(); } } ... } ...}
注册Observable对象监听
- 入口 updateRegistration(0, contact) ：
protected boolean updateRegistration(int localFieldId, Observable observable) { return updateRegistration(localFieldId, observable, CREATE_PROPERTY_LISTENER);}
private boolean updateRegistration(int localFieldId, Object observable, CreateWeakListener listenerCreator) { ... // 确保不重复监听，先移除再添加观察监听 unregisterFrom(localFieldId); registerTo(localFieldId, observable, listenerCreator); return true;}
protected void registerTo(int localFieldId, Object observable, CreateWeakListener listenerCreator) { if (observable == null) { return; }
// 创建对象监听并存到mLocalFieldObservers中 WeakListener listener = mLocalFieldObservers[localFieldId]; if (listener == null) { // CREATE_PROPERTY_LISTENER -> create(...) listener = listenerCreator.create(this, localFieldId); mLocalFieldObservers[localFieldId] = listener; }
// 将监听绑定到Observable对象上 listener.setTarget(observable);}
每个Observable对象都会添加一个观察监听，保存在数组 mLocalFieldObservers 中，并以 localFieldId 索引。
- CREATE_PROPERTY_LISTENER 为何物？
private static final CreateWeakListener CREATE_PROPERTY_LISTENER = new CreateWeakListener() { @Override public WeakListener create(ViewDataBinding viewDataBinding, int localFieldId) { // 返回从WeakPropertyListener实例中获取的监听器(WeakListener) return new WeakPropertyListener(viewDataBinding, localFieldId).getListener(); }}
private static class WeakPropertyListener extends Observable.OnPropertyChangedCallback implements ObservableReference<Observable> { final WeakListener<Observable> mListener;
public WeakPropertyListener(ViewDataBinding binder, int localFieldId) { mListener = new WeakListener<Observable>(binder, localFieldId, this); }
@Override public WeakListener<Observable> getListener() { return mListener; }
@Override public void addListener(Observable target) { // WeakPropertyListener 继承于 Observable.OnPropertyChangedCallback， // 所以 this 其实就是 Observable对象的属性监听器 target.addOnPropertyChangedCallback(this); }
...}
private static class WeakListener<T> extends WeakReference<ViewDataBinding> { private final ObservableReference<T> mObservable; protected final int mLocalFieldId; private T mTarget;
...
public void setTarget(T object) { unregister(); mTarget = object; if (mTarget != null) { // mObservable 是上面的 WeakPropertyListener对象 // mTarget 是绑定到listener上得Observable对象 mObservable.addListener(mTarget); } }
...}
CREATE_PROPERTY_LISTENER 实际上只是一个接口实例，注册时会调用它的create()方法创建一个弱引用listener，它的作用是将listener绑定到Observable对象上，
绑定时，会调用 listener.setTarget(…) 将Observable对象传给 WeakPropertyListener实例，然后，WeakPropertyListener 会为 Observable对象添加OnPropertyChangedCallback。
- addOnPropertyChangedCallback实现
addOnPropertyChangedCallback 在 BaseObservable中实现，首先会实例化一个PropertyChangeRegistry对象，同时创建一个用来通知Observable对象重新绑定更新的回调CallbackRegistry.NotifierCallback。然后将 OnPropertyChangedCallback 添加到PropertyChangeRegistry的回调列表中
@Overridepublic synchronized void addOnPropertyChangedCallback(OnPropertyChangedCallback callback) { if (mCallbacks == null) { mCallbacks = new PropertyChangeRegistry(); } mCallbacks.add(callback);}
这样，注册Observable对象的监听就完毕了。
更新(重新绑定)Observable对象
设置或更新Observable对象时都会调用notifyPropertyChanged()或notifyChange()来通知更新，那到底是如何更新的呢？
- 回调过程
public void notifyPropertyChanged(int fieldId) { // mCallbacks 是 PropertyChangeRegistry对象，在 addOnPropertyChangedCallback 时实例化 // 如果注册了Observable对象监听，那么mCallbacks不为null if (mCallbacks != null) { mCallbacks.notifyCallbacks(this, fieldId, null); }}
// baseLibraryprivate void notifyCallbacks(T sender, int arg, A arg2, int startIndex, int endIndex, long bits) { long bitMask = 1L; for(int i = startIndex; i < endIndex; ++i) { if((bits & bitMask) == 0L) { // mNotifier 是实例化PropertyChangeRegistry时创建的 // mNotifier 即 CallbackRegistry.NotifierCallback this.mNotifier.onNotifyCallback(this.mCallbacks.get(i), sender, arg, arg2); } bitMask <<= 1; }}
// PropertyChangeRegistry.NOTIFIER_CALLBACKpublic void onNotifyCallback(Observable.OnPropertyChangedCallback callback, Observable sender, int arg, Void notUsed) { // callback 是为Observable对象添加的OnPropertyChangedCallback，即WeakPropertyListener callback.onPropertyChanged(sender, arg);}
// WeakPropertyListenerpublic void onPropertyChanged(Observable sender, int propertyId) { // binder 即生成的Binding类对象 ViewDataBinding binder = mListener.getBinder(); ... binder.handleFieldChange(mListener.mLocalFieldId, sender, propertyId);}
private void handleFieldChange(int mLocalFieldId, Object object, int fieldId) { // onFieldChange 实现在生成的Binding类中 boolean result = onFieldChange(mLocalFieldId, object, fieldId); if (result) { // 如果对象属性变化，将重新绑定 requestRebind(); }}
通过 notifyPropertyChanged 调用到 mNotifier 回调， mNotifier 通知OnPropertyChangedCallback Observable对象属性发生变化，然后在onPropertyChanged中又转给ViewDataBinding对象(生成的Binding类)处理。
- 判断是否需要重新绑定并执行，在生成的Binding类中实现
// 生成的Binding类中得方法protected boolean onFieldChange(int localFieldId, Object object, int fieldId) { // 如果变量不是Observable类型或没有添加 Bindable注解，就不会判断，直接返回false switch (localFieldId) { case 0 : return onChangeContact((com.connorlin.databinding.model.ObservableContact) object, fieldId); } return false;}
private boolean onChangeContact(com.connorlin.databinding.model.ObservableContact contact, int fieldId) { switch (fieldId) { case BR.name: { synchronized(this) { mDirtyFlags |= 0x4L;// 通过mDirtyFlags判断对象是否变化 } return true; } ... } return false;}
至此，更新过程完毕。
整个注册与更新过程可以用一张流程图来概括：
事件处理
事件处理的原理很简单，在生成Binding类中会实现View事件的监听，在构造时实例化View的事件监听，然后在绑定时将事件监听对象赋值给对应View，这样，点击时就会触发相应的监听。
这里以 DataBindingDemo 中 EventActivity部分为例：
- 生成的Binding类并实现View的事件监听
public class ActivityEventBinding extends Android.databinding.ViewDataBinding implements Android.databinding.generated.callback.OnCheckedChangeListener.Listener, Android.databinding.generated.callback.OnClickListener.Listener { // Checkbox check监听 private final Android.widget.CompoundButton.OnCheckedChangeListener mCallback3; private final Android.view.View.OnClickListener mCallback2; private final Android.view.View.OnClickListener mCallback1; // listeners private OnClickListenerImpl mAndroidViewViewOnCl; ... // Listener Stub Implementations public static class OnClickListenerImpl implements Android.view.View.OnClickListener{ private com.connorlin.databinding.handler.EventHandler value; public OnClickListenerImpl setValue(com.connorlin.databinding.handler.EventHandler value) { this.value = value; return value == null ? null : this; } @Override public void onClick(Android.view.View arg0) { this.value.onClickFriend(arg0); } } ...}
- 实例化View的事件监听
public ActivityEventBinding(Android.databinding.DataBindingComponent bindingComponent, View root) { super(bindingComponent, root, 0); ... // listeners mCallback3 = new Android.databinding.generated.callback.OnCheckedChangeListener(this, 3); mCallback2 = new Android.databinding.generated.callback.OnClickListener(this, 2); mCallback1 = new Android.databinding.generated.callback.OnClickListener(this, 1); invalidateAll();}
- 在执行绑定中绑定View事件监听
@Overrideprotected void executeBindings() { ... if ((dirtyFlags & 0x6L) != 0) { if (handler != null) { // read handler::onClickFriend AndroidViewViewOnCli = (((mAndroidViewViewOnCl == null) ? (mAndroidViewViewOnCl = new OnClickListenerImpl()) : mAndroidViewViewOnCl).setValue(handler)); } } // batch finished if ((dirtyFlags & 0x6L) != 0) { this.mboundView1.setOnClickListener(AndroidViewViewOnCli); } if ((dirtyFlags & 0x4L) != 0) { this.mboundView2.setOnClickListener(mCallback1); this.mboundView3.setOnClickListener(mCallback2); Android.databinding.adapters.CompoundButtonBindingAdapter.setListeners( this.mboundView4, mCallback3, (Android.databinding.InverseBindingListener)null); }}
- 触发事件并执行
ViewStub
原理类似，只是利用 ViewStubProxy 来延迟绑定。
- 使用layout中的ViewStub实例化一个ViewStubProxy对象赋给viewstub变量，并与Bingding关联
public ActivityViewStubBinding(Android.databinding.DataBindingComponent bindingComponent, View root) { super(bindingComponent, root, 0); final Object[] bindings = mapBindings(bindingComponent, root, 2, sIncludes, sViewsWithIds); ... this.viewStub = new Android.databinding.ViewStubProxy((Android.view.ViewStub) bindings[1]); this.viewStub.setContainingBinding(this); ...}
- 实例化ViewStubProxy的同时会注册inflate监听
private OnInflateListener mProxyListener = new OnInflateListener() { @Override public void onInflate(ViewStub stub, View inflated) { mRoot = inflated; mViewDataBinding = DataBindingUtil.bind(mContainingBinding.mBindingComponent, inflated, stub.getLayoutResource()); mViewStub = null;
if (mOnInflateListener != null) { mOnInflateListener.onInflate(stub, inflated); mOnInflateListener = null; } mContainingBinding.invalidateAll(); mContainingBinding.forceExecuteBindings(); }};
public ViewStubProxy(ViewStub viewStub) { mViewStub = viewStub; mViewStub.setOnInflateListener(mProxyListener);}
- inflate ViewStub
if (!mActivityViewStubBinding.viewStub.isInflated()) { mActivityViewStubBinding.viewStub.getViewStub().inflate();}
当ViewStub infate时，执行mProxyListener，其中会生成ViewStub的Binding，并强制执行主Binding重绑
- 绑定ViewStub
@Overrideprotected void executeBindings() { long dirtyFlags = 0; synchronized(this) { dirtyFlags = mDirtyFlags; mDirtyFlags = 0; } // batch finished if (viewStub.getBinding() != null) { viewStub.getBinding().executePendingBindings(); }}
这样，ViewStub绑定就结束了。
时间： 2024-09-24 22:58:20