Lifecycle簡介
官方簡介如此:
Lifecycle-aware components perform actions in response to a change in the lifecycle status of another component, such as activities and fragments. These components help you produce better-organized, and often lighter-weight code, that is easier to maintain.
生命週期感知組件可以響應另一個組件生命週期的變化(例如Activity和Fragment的生命週期狀態更改)。 這些(實現了Lifecycle的)組件可幫助你構建組織性更好、更輕、更易於維護的代碼。
聽起來很強大吧,先來來看看使用效果吧。
Lifecycle網絡回調示例
常規RxJava&Retrofit網絡回調:
@Deprecated
private void getData(){
new MyApi().getGankMeizhi(20)
.subscribe(new OldObserver<GankMeizhi>() {
@Override
public void onSubscribe(Disposable d) {
//需記錄然後手動釋放該Disposable。
}
@Override
public void onNext(GankMeizhi gankMeizhi) {
//需判斷是否可以安全地執行UI刷新。
if (isFinishing()){
return;
}
if (!gankMeizhi.error) {
mMyAdapter.refreshData(gankMeizhi);
}
}
});
}
實現了Lifecycle的RxJava&Retrofit網絡安全回調:
private void getDataSafe() {
new MyApi().getGankMeizhi(20)
.subscribe(new SafeObserver<GankMeizhi>(getLifecycle()) {
@Override
public void onNext(GankMeizhi gankMeizhi) {
//可以安全地執行UI操作。
if (!gankMeizhi.error) {
mMyAdapter.refreshData(gankMeizhi);
}
}
});
}
可以發現,結合Lifecycle,回調不僅簡潔,而且更爲安全。Lifecycle可以讓開發者更專注地實現功能而非小心翼翼地做生命週期判斷。
如何實現
首先,我們Lifecycle庫引入到項目。在app模塊build.gradle文件dependencies內添加以下代碼即可:
// Java8 support for Lifecycles
implementation 'android.arch.lifecycle:common-java8:1.1.1'
接着,我們爲自定義的RxObserver實現LifecycleObserver接口:
import android.arch.lifecycle.Lifecycle;
import android.arch.lifecycle.LifecycleObserver;
import android.arch.lifecycle.OnLifecycleEvent;
import android.util.Log;
import io.reactivex.Observer;
import io.reactivex.disposables.Disposable;
/**
* 一個生命週期安全的RxObserver。
* Created on 2018/4/18.
*
* @author ice
*/
public abstract class SafeObserver<T> implements LifecycleObserver, Observer<T> {
public static final String TAG = "SafeObserver";
private Lifecycle mLifecycle;
private Disposable mDisposable;
/*不傳入Lifecycle,手動管理該Observer的生命週期*/
public SafeObserver() {
//unSafe
}
/*傳入Lifecycle,自動保證回調安全*/
public SafeObserver(Lifecycle lifecycle) {
//lifecycle safe.
mLifecycle = lifecycle;
}
@Override
public void onSubscribe(Disposable d) {
mDisposable = d;
if (mLifecycle != null)
mLifecycle.addObserver(this); //加入到lifecycle觀察者。
}
@Override
public void onError(Throwable e) {
e.printStackTrace();
onEnd();
}
@Override
public void onComplete() {
onEnd();
}
protected void onEnd() {
Log.i(TAG, "onEnd");
onDisPose(); //RxObserver結束後自動釋放。
}
/*釋放Rx觀察者(在Lifecycle的ON_DESTROY事件發生時會自動調用該方法)*/
@OnLifecycleEvent(Lifecycle.Event.ON_DESTROY)
public void onDisPose() {
Log.i(TAG, "dispose");
if (mLifecycle != null)
mLifecycle.removeObserver(this);//解除與lifecycle的綁定。
if (mDisposable != null && !mDisposable.isDisposed())
mDisposable.dispose();
}
}
然後,我們需要爲Activity(或Fragment)實現LifecycleOwner接口(AppCompatActivity與v4Fragment已實現)。
我們需要在Activity(或Fragment)生命週期中處理Lifecycle事件(在Base類裏做一次即可,2018年8月補充:高版本的buildTools已經不需要手動處理):
//AppCompatActivity與v4Fragment自帶LifecycleRegistry,所以通過強轉獲取即可。
protected LifecycleRegistry mLifecycleRegistry = (LifecycleRegistry) getLifecycle();
@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
//...
handleLifecycleEvent(Lifecycle.Event.ON_CREATE);
}
@Override
protected void onStart() {
super.onStart();
handleLifecycleEvent(Lifecycle.Event.ON_START);
}
@Override
protected void onResume() {
super.onResume();
handleLifecycleEvent(Lifecycle.Event.ON_RESUME);
}
@Override
protected void onPause() {
handleLifecycleEvent(Lifecycle.Event.ON_PAUSE);
super.onPause();
}
@Override
protected void onStop() {
handleLifecycleEvent(Lifecycle.Event.ON_STOP);
super.onStop();
}
@Override
protected void onDestroy() {
handleLifecycleEvent(Lifecycle.Event.ON_DESTROY);
super.onDestroy();
}
public void handleLifecycleEvent(@NonNull Lifecycle.Event event) {
mLifecycleRegistry.handleLifecycleEvent(event);
}
好了,大功告成!這樣一來,訂閱該lifecycle的觀察者(比如前面的SafeObserver)就能接收到該lifecycle對應Activity(或Fragment)生命週期的回調了。
相關資料
本文Demo: LifecyclePractice
使用了Lifecycle的一個輕圖文App: Now
Lifecycle官方文檔: Handling Lifecycles with Lifecycle-Aware Components