作者:xcheng_ 链接:https://www.jianshu.com/p/07fe489a53f2 声明:本文已获
xcheng_
投稿发表,转发等请联系原作者授权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
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
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。 lifecycle代码简洁,我们可以通过实现LifecycleObserver 接口,来监听声明周期,然后我们在activity和fragment中去注册监听。
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 ArrayList<Observer> mObservers = 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
RealCall
final class RealCall<T> implements Call<T> { //忽略其他代码 @Override public LifeCall<T> 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<T> bindUntilDestroy(LifecycleProvider provider) { return bindToLifecycle(provider, Lifecycle.Event.ON_DESTROY); } }LifecycleProvider.Observer
,因此可以在onChanged
方法接收分发的Lifecycle.Event
public interface LifeCall<T> extends Callable<T>, 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. * <p> * like {@code Observable#doOnDispose(Action)},{@code SingleSubject#onSuccess(Object)} * <p> * you can invoke with {@link Lifecycle.Event#ON_ANY} to dispose from outside immediately. */ @Override void onChanged(@NonNull Lifecycle.Event event); }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<T> implements LifeCall<T> { private final Call<T> delegate; private final Lifecycle.Event event; private final LifecycleProvider provider; private final AtomicBoolean once = new AtomicBoolean(); RealLifeCall(Call<T> 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(); } }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<Foo> or %s<? extends Foo>", 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<Object, Call<?>>() { @Override public Type responseType() { return responseType; } @Override public Call<Object> adapt(retrofit2.Call<Object> call) { if (executor != null) { return new RealCall<>(executor, call); } return new RealCall<>(OPTIONAL_NULL_EXECUTOR, call); } }; } }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<T> { /** * @param call The {@code Call} that was started */ void onStart(Call<T> call); @NonNull HttpError parseThrowable(Call<T> 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<T> call, T t); void onError(Call<T> call, HttpError error); void onSuccess(Call<T> call, T t); /** * @param t 请求失败的错误信息 */ void onCompleted(Call<T> call, @Nullable Throwable t); }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
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 toMainThread.to(new Runnable() { @Override public void run() { Toast.makeText(MainActivity.this, "登录成功", Toast.LENGTH_SHORT).show(); } }, Lifecycle.Event.ON_STOP); } catch (Throwable throwable) { //异常处理,这里只做简单的演示 //你可以对throwable做解析分类 toMainThread.to(new Runnable() { @Override public void run() { Toast.makeText(MainActivity.this, "服务异常", Toast.LENGTH_SHORT).show(); } }, Lifecycle.Event.ON_STOP); } } };github 地址: https://github.com/xchengDroid/retrofit-helper
欢迎提出疑问和建议。