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http请求一直是开发中无法避免的存在,生命周期的管理也一直是开发者的痛点,稍不注意就在回调是抛出异常,如NullPointerException,showDialog导致的WindowLeaked等。
Google 最新推荐的 Lifecycle 架构就是可以让你自己的类拥有像 activity 或 fragment 一样生命周期的功能。
于是我决定采用lifecycle结合retrofit 将http请求和Activity或Fragment的生命周期相结合
本文将从以下几个方面一步步实现功能
多线程分发Lifecycle. Event
retrofit如何与其关联?自定义 CallAdapter.Factory
异步请求如何关联
同步请求如何关联
如果有不熟悉lifecycle的可以自行学习,这里不做介绍了
lifecycle官方文档地址:
https://developer.android.com/topic/libraries/architecture/lifecycle
为什么要使用lifecycle?
activity 和fragment 是有声明周期的,有时候,我们的很多操作需要写在声明周期的方法中,比如,下载,文件操作等,这样很多情况下回导致,我们在activity中的声明周期方法中写越来越多的代码,activity或者fragment 越来越臃肿,代码维护越来越困难。使用lifecycle就可以很好的解决这类问题。
一 、分发lifecycle event
对于event的分发我们采用观察者模式,需要支持多线程环境,因为http请求可能在任意线程中发起。
首先定义一个 LifecycleProvider
类,如下
/** * 统一分发Activity和 Fragment的生命周期时间. */public interface LifecycleProvider { /** * Adds an observer to the list. The observer cannot be null and it must not already * be registered. * * @param observer the observer to register * @throws IllegalArgumentException the observer is null */ void observe(Observer observer); /** * Removes a previously registered observer. The observer must not be null and it * must already have been registered. * * @param observer the observer to unregister * @throws IllegalArgumentException the observer is null */ void removeObserver(Observer observer); /** * A simple callback that can receive from {@link android.arch.lifecycle.Lifecycle} */ interface Observer { /** * Called when the event is changed. * * @param event The new event */ void onChanged(@NonNull Lifecycle.Event event); }}
实现类 为AndroidLifecycle
继承了LifecycleObserver
接口监听Lifecycle event
public final class AndroidLifecycle implements LifecycleProvider, LifecycleObserver { private final Object mLock = new Object(); @GuardedBy("mLock") private final ArrayListmObservers = new ArrayList<>(); /** * 缓存当前的Event事件 */ @GuardedBy("mLock") @Nullable private Lifecycle.Event mEvent; @MainThread public static LifecycleProvider createLifecycleProvider(LifecycleOwner owner) { return new AndroidLifecycle(owner); } private AndroidLifecycle(LifecycleOwner owner) { owner.getLifecycle().addObserver(this); } @OnLifecycleEvent(Lifecycle.Event.ON_ANY) void onEvent(LifecycleOwner owner, Lifecycle.Event event) { synchronized (mLock) { //保证线程的可见性 mEvent = event; for (int i = mObservers.size() - 1; i >= 0; i--) { mObservers.get(i).onChanged(event); } } if (event == Lifecycle.Event.ON_DESTROY) { owner.getLifecycle().removeObserver(this); } } @Override public void observe(Observer observer) { if (observer == null) { throw new IllegalArgumentException("The observer is null."); } synchronized (mLock) { if (mObservers.contains(observer)) { return; } mObservers.add(observer); if (mEvent != null) { observer.onChanged(mEvent); } } } @Override public void removeObserver(Observer observer) { if (observer == null) { throw new IllegalArgumentException("The observer is null."); } synchronized (mLock) { int index = mObservers.indexOf(observer); if (index == -1) { return; } mObservers.remove(index); } }}
使用时只要在onChanged方法中就可以处理对应的事件,使用如下
LifecycleProvider provider = AndroidLifecycle.createLifecycleProvider(this); @Override protected void onCreate(@Nullable Bundle savedInstanceState) { super.onCreate(savedInstanceState); provider.observe(new LifecycleProvider.Observer() { @Override public void onChanged(@NonNull Lifecycle.Event event) { //do... } }); }
observe
方法不依赖于主线程,可以在任何地方调用。这样二次分发设计的目的有两个
owner.getLifecycle().addObserver(LifecycleObserver)
方法是线程不安全的,需要依赖主线程可以缓存最新的Lifecycle.Event
二、retrofit 关联生命周期
retrofit 如何才能关联生命周期呢,通用的做法肯定是自定义CallAdapter.Factory
,我们可以返回我们想要的自定义Call,在Call接口添加bindToLifecycle
方法于LifecycleProvider
相关联
自定义Call接口如下,添加了绑定生命周期的方法,这里只展示核心方法
public interface Call
extends Callable , Cloneable { //忽略其他代码 /** * 绑定生命周期 * * @param provider LifecycleProvider * @param event {@link Lifecycle.Event}, {@link Lifecycle.Event#ON_ANY} is not allowed * @return LifeCall */ LifeCall bindToLifecycle(LifecycleProvider provider, Lifecycle.Event event); /** * default event is {@link Lifecycle.Event#ON_DESTROY} * * @param provider LifecycleProvider * @return LifeCall * @see Call#bindToLifecycle(LifecycleProvider, Lifecycle.Event) */ LifeCall bindUntilDestroy(LifecycleProvider provider);} 且看如何实现此接口
RealCall
final class RealCall
implements Call { //忽略其他代码 @Override public LifeCall bindToLifecycle(LifecycleProvider provider, Lifecycle.Event event) { Utils.checkNotNull(provider, "provider==null"); Utils.checkNotNull(event, "event==null"); if (event == Lifecycle.Event.ON_ANY) { throw new IllegalArgumentException("ON_ANY event is not allowed."); } return new RealLifeCall<>(clone(), event, provider); } @Override public LifeCall bindUntilDestroy(LifecycleProvider provider) { return bindToLifecycle(provider, Lifecycle.Event.ON_DESTROY); }} LifeCall 生命周期管理的接口类,它继承了
LifecycleProvider.Observer
,因此可以在onChanged
方法接收分发的Lifecycle.Eventpublic interface LifeCall
extends Callable , LifecycleProvider.Observer { /** * Returns true if this call has been disposed. * * @return true if this call has been disposed */ boolean isDisposed(); /** * The method may be called concurrently from multiple * threads; the method must be thread safe. Calling this method multiple * times has no effect. * * like {@code Observable#doOnDispose(Action)},{@code SingleSubject#onSuccess(Object)} *
* you can invoke with {@link Lifecycle.Event#ON_ANY} to dispose from outside immediately. */ @Override void onChanged(@NonNull Lifecycle.Event event);}
且看如何实现此接口
RealLifeCall
在
onChanged
中判断,当event参数为指定的event时取消请求,并且标记为disposed,从provider中移除RealLifeCall
观察对象。注意的是可以手动调用LifeCall.onChanged(LifeCycle.Event.ON_ANY)
取消请求用于你想处理的任何场景,如果isDisposed()
返回为true,在异步Callback调用的情况下是不会回调的。final class RealLifeCall
implements LifeCall { private final Call delegate; private final Lifecycle.Event event; private final LifecycleProvider provider; private final AtomicBoolean once = new AtomicBoolean(); RealLifeCall(Call delegate, Lifecycle.Event event, LifecycleProvider provider) { this.delegate = delegate; this.event = event; this.provider = provider; provider.observe(this); } //忽略其他代码 @Override public void onChanged(@NonNull Lifecycle.Event event) { if (this.event == event || event == Lifecycle.Event.ON_DESTROY //Activity和Fragment的生命周期是不会传入 {@code Lifecycle.Event.ON_ANY}, //可以手动调用此方法传入 {@code Lifecycle.Event.ON_ANY},用于区分是否为手动调用 || event == Lifecycle.Event.ON_ANY) { if (once.compareAndSet(false, true)/*保证原子性*/) { delegate.cancel(); provider.removeObserver(this); } } } @Override public boolean isDisposed() { return once.get(); }} 如何返回Call ?自定义
CallAdapter.Factory
retrofit的解耦灵活我们可以做很多自定义的配置,自定义Factory返回我们的
Call
接口对象,只需在创建retrofit对象是调用addCallAdapterFactory(CallAdapterFactory.INSTANCE)
添加进去即可。注:executor默认为Android主线程调度使用,
Callback
回调函数会在对应线程执行。详情可以看retrofit2.Platform.Android.defaultCallbackExecutor()
方法public final class CallAdapterFactory extends CallAdapter.Factory { private static final String RETURN_TYPE = Call.class.getSimpleName(); public static final CallAdapter.Factory INSTANCE = new CallAdapterFactory(); private static final Executor OPTIONAL_NULL_EXECUTOR = new Executor() { @Override public void execute(@NonNull Runnable command) { command.run(); } }; private CallAdapterFactory() { } @Override public CallAdapter get(Type returnType, Annotation[] annotations, Retrofit retrofit) { if (getRawType(returnType) != Call.class) { return null; } if (!(returnType instanceof ParameterizedType)) { throw new IllegalArgumentException( String.format("%s return type must be parameterized as %s
or %s ", RETURN_TYPE, RETURN_TYPE, RETURN_TYPE)); } final Type responseType = getParameterUpperBound(0, (ParameterizedType) returnType); final Executor executor = Utils.isAnnotationPresent(annotations, SkipCallbackExecutor.class) ? null : retrofit.callbackExecutor(); return new CallAdapter 丰富的
Callback
接口支持开始、结束、成功、失败、异常统一解析、简单的数据二次处理操作,
HttpError
统一包装异常信息public interface Callback
{ /** * @param call The {@code Call} that was started */ void onStart(Call call); @NonNull HttpError parseThrowable(Call call, Throwable t); /** * 过滤一次数据,如剔除List中的null等,默认可以返回t */ @NonNull T transform(Call call, T t); void onError(Call call, HttpError error); void onSuccess(Call call, T t); /** * @param t 请求失败的错误信息 */ void onCompleted(Call call, @Nullable Throwable t);} 异步调用
定义接口
@FormUrlEncoded@POST("user/login")Call
getLogin(@Field("username") String username, @Field("password") String password); 安全的异步发起请求:
public class MainActivity extends AppCompatActivity { LifecycleProvider provider = AndroidLifecycle.createLifecycleProvider(this); @Override protected void onCreate(@Nullable Bundle savedInstanceState) { super.onCreate(savedInstanceState); RetrofitFactory.create(ApiService.class) .getLogin("loginName", "password") //.bindUntilDestroy(provider) .bindToLifecycle(provider, Lifecycle.Event.ON_STOP) .enqueue(new DefaultCallback
() { @Override public void onStart(Call call) { showLoading(); } @Override public void onError(Call call, HttpError error) { Toast.makeText(MainActivity.this, error.msg, Toast.LENGTH_SHORT).show(); } @Override public void onSuccess(Call call, LoginInfo loginInfo) { Toast.makeText(MainActivity.this, "登录成功", Toast.LENGTH_SHORT).show(); } @Override public void onCompleted(Call call, @Nullable Throwable t){ hideLoading(); } }); }} 如何同步调用
一般同步调用的场景不多,一些连续且相互依赖的请求可以使用同步请求减少逻辑复杂性
如:注册成功后直接登录,如果采用异步的方式实现,回调接口缠绕在一起,代码不好维护。采用同步的方式实现更为方便。
@FormUrlEncoded@POST("user/register")Call
register(@Field("username") String username, @Field("password") String password);@FormUrlEncoded@POST("user/login")Call getLogin(@Field("username") String username, @Field("password") String password); new Thread(){ @Override public void run() { super.run(); try { RegisterInfo registerInfo=RetrofitFactory.create(ApiService.class) .register("loginName", "password") .bindToLifecycle(provider, Lifecycle.Event.ON_STOP) .execute(); //注册成功开始登录 LoginInfo loginInfo=RetrofitFactory.create(ApiService.class) .getLogin("loginName", "password") .bindToLifecycle(provider, Lifecycle.Event.ON_STOP) .execute(); //登录成功 } catch (Throwable throwable) { //异常处理 throwable.printStackTrace(); } }}.start();
这里涉及二个问题
关于Thread,可以自行用线程池实现,这里制作演示
线程调度,成功和失败的结果需要回调到主线程中,android中回调主线程采用的
Handler.post(Runnable)
或者postDelayed(Runnable, long)
方法实现,当主线程调度执行run
方法是可能Activity或者Fragment已经被销毁。那么怎样才能安全的回调到主线程呢?调度方法和生命周期关联,在主线程执行时再次做判断。NetTaskExecutor 是做的Handler的封装
public final class ToMainThread implements LifecycleProvider.Observer { @Nullable private volatile Lifecycle.Event mEvent; private final LifecycleProvider provider; public ToMainThread(LifecycleProvider provider) { this.provider = provider; provider.observe(this); } public void to(@NonNull final Runnable runnable, final Lifecycle.Event event) { NetTaskExecutor.getInstance().postToMainThread(new Runnable() { @Override public void run() { if (mEvent == event || mEvent == Lifecycle.Event.ON_DESTROY) return; runnable.run(); } }); } public void toDelayed(@NonNull final Runnable runnable, final Lifecycle.Event event, long delayMillis) { NetTaskExecutor.getInstance().postToMainThreadDelayed(new Runnable() { @Override public void run() { if (mEvent == event || mEvent == Lifecycle.Event.ON_DESTROY) return; runnable.run(); } }, delayMillis); } @Override public void onChanged(@NonNull Lifecycle.Event event) { this.mEvent = event; if (event == Lifecycle.Event.ON_DESTROY) { provider.removeObserver(this); } }}
完整的同步执行代码如下,这样处理完全关联了生命周期。不会出任何问题
结束
github 地址:https://github.com/xchengDroid/retrofit-helper
欢迎提出疑问和建议。
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