LiveData升级版 LiveData升级版

前言
系统的Livedata由于内部使用ObserverWrapper封装Observer，通过粘性效果实现通知，有些时候不需要粘性通知，需要在订阅之后再观察事件，通过反射修改如下：

public class BusMutableLiveData extends MutableLiveData {@Override public void observe(@NonNull LifecycleOwner owner, @NonNull Observer observer) { super.observe(owner, observer); hook(observer); }private void hook(Observer observer) { Class liveDataClass = LiveData.class; try { //获取field private SafeIterableMap, ObserverWrapper> mObservers Field mObservers = liveDataClass.getDeclaredField("mObservers"); mObservers.setAccessible(true); //获取SafeIterableMap集合mObservers Object observers = mObservers.get(this); Class observersClass = observers.getClass(); //获取SafeIterableMap的get(Object obj)方法 Method methodGet = observersClass.getDeclaredMethod("get", Object.class); methodGet.setAccessible(true); //获取到observer在集合中对应的ObserverWrapper对象 Object objectWrapperEntry = methodGet.invoke(observers, observer); Object objectWrapper = null; if (objectWrapperEntry instanceof Map.Entry) { objectWrapper = ((Map.Entry) objectWrapperEntry).getValue(); } if (objectWrapper == null) { throw new NullPointerException("ObserverWrapper can not be null"); } //获取ObserverWrapper的Class对象LifecycleBoundObserver extends ObserverWrapper Class wrapperClass = objectWrapper.getClass().getSuperclass(); //获取ObserverWrapper的field mLastVersion Field mLastVersion = wrapperClass.getDeclaredField("mLastVersion"); mLastVersion.setAccessible(true); //获取liveData的field mVersion Field mVersion = liveDataClass.getDeclaredField("mVersion"); mVersion.setAccessible(true); Object mV = mVersion.get(this); //把当前ListData的mVersion赋值给 ObserverWrapper的field mLastVersion mLastVersion.set(objectWrapper, mV); mObservers.setAccessible(false); methodGet.setAccessible(false); mLastVersion.setAccessible(false); mVersion.setAccessible(false); } catch (Exception e) { e.printStackTrace(); } } }

封装
【LiveData升级版】上面试Livedata的封装，平时使用的情况下简化过程，封装工具类如下：

public class LiveDataBus {private final Map> mBus; private LiveDataBus() { mBus = new ArrayMap<>(); }private static abstract class SingleHolder { private static final LiveDataBus DATA_BUS = new LiveDataBus(); }public static LiveDataBus get() { return SingleHolder.DATA_BUS; }/** * 订阅事件 * * @param event */ public void subscribe(T event) { if (null == event) { throw new IllegalArgumentException("Subscribed events must be not null!"); }String eventName = event.getClass().getName(); if (!mBus.containsKey(eventName)) { mBus.put(eventName, new BusMutableLiveData<>()); }BusMutableLiveData liveData = https://www.it610.com/article/mBus.get(eventName); if (null != liveData) { liveData.setValue(event); } }/** * 观察事件 * * @param eventType * @return */ public T observable(Class eventType) { String eventName = eventType.getName(); if (TextUtils.isEmpty(eventName)) { throw new IllegalArgumentException("Observered events must be not null!"); } return mBus.get(eventName).getValue(); }/** * 观察事件 * * @param eventType * @return */ public LiveData postObservable(Class eventType) { String eventName = eventType.getName(); if (TextUtils.isEmpty(eventName)) { throw new IllegalArgumentException("Observered events must be not null!"); } BusMutableLiveData tBusMutableLiveData = https://www.it610.com/article/mBus.get(eventName); if(tBusMutableLiveData==null) { throw new IllegalArgumentException("The event you observe has not been subscribed!"); } return mBus.get(eventName); }}

第二种

public class LifecycleBus {private MutableLiveData liveData; public final static boolean MODE_SYSTEM = false; private LifecycleBus() { }private static abstract class SingleHolder { private static final LifecycleBus DATA_BUS = new LifecycleBus(); }public static LifecycleBus get() { return LifecycleBus.SingleHolder.DATA_BUS; }/** * 订阅事件 * * @param event */ protected void subscribe(T event) { subscribe(MODE_SYSTEM,event); }/** * 订阅事件 * * @param event */ protected void subscribe(boolean useSystem,T event) { if (null == event) { throw new IllegalArgumentException("Subscribed events must be not null!"); } liveData = https://www.it610.com/article/useSystem ? new MutableLiveData() : new LifecycleLiveData(); liveData.setValue(event); }/** * 观察事件 * * @param activity * @param observer */ public void observe(@NonNull AppCompatActivity activity, @NonNull Observer observer) { if (liveData =https://www.it610.com/article/= null) { throw new IllegalArgumentException("The event you observe has not been subscribed!"); } if (liveData instanceof LifecycleLiveData) { LifecycleLiveData lifecycleLiveData = https://www.it610.com/article/(LifecycleLiveData) liveData; lifecycleLiveData.observe(activity, observer); } else { liveData.observe(activity, observer); } }/** * 观察事件 * * @param fragment * @param observer */ public void observe(@NonNull Fragment fragment, @NonNull Observer observer) { if (liveData =https://www.it610.com/article/= null) { throw new IllegalArgumentException("The event you observe has not been subscribed!"); } if (liveData instanceof LifecycleLiveData) { LifecycleLiveData lifecycleLiveData = https://www.it610.com/article/(LifecycleLiveData) liveData; lifecycleLiveData.observe(fragment, observer); } else { liveData.observe(fragment, observer); } }/** * 内部类继承 * MutableLiveData * * @param */ public class LifecycleLiveData extends MutableLiveData {private final HashMap observers = new HashMap<>(); public void observe(@NonNull AppCompatActivity activity, @NonNull Observer observer) { LifecycleOwner owner = activity; Integer storeId = System.identityHashCode(activity.getViewModelStore()); observe(storeId, owner, observer); }public void observe(@NonNull Fragment fragment, @NonNull Observer observer) { LifecycleOwner owner = fragment.getViewLifecycleOwner(); Integer storeId = System.identityHashCode(fragment.getViewModelStore()); observe(storeId, owner, observer); }private void observe(@NonNull Integer storeId, @NonNull LifecycleOwner owner, @NonNull Observer observer) { if (observers.get(storeId) == null) { observers.put(storeId, true); } super.observe(owner, t -> { if (!observers.get(storeId)) { observers.put(storeId, true); } if (t != null) { observer.onChanged(t); } }); }/** * 禁用此方法 * * @param observer */ @Override public void observe(@NonNull LifecycleOwner owner, @NonNull Observer observer) { }/** * 禁用此方法 * * @param observer */ @Override public void observeForever(@NonNull Observer observer) { }@Override public void setValue(T value) { if (value != null) { for (Map.Entry entry : observers.entrySet()) { entry.setValue(false); } super.setValue(value); } }/** * 清理 */ public void clear() { super.setValue(null); } }}