做网站插背景图片如何变大,交互式网站定义,idea15网站开发,wordpress google翻译插件现在很多Android App的开发开始使用Rxjava#xff0c;但是Rxjava以学习曲线陡峭著称#xff0c;入门有些困难。经过一段时间的学习和使用#xff0c;这里来介绍一下我对Rxjava的理解。 说到Rxjava首先需要了解的两个东西#xff0c;一个是Observable#xff08;被观察者但是Rxjava以学习曲线陡峭著称入门有些困难。经过一段时间的学习和使用这里来介绍一下我对Rxjava的理解。 说到Rxjava首先需要了解的两个东西一个是Observable被观察者事件源和 Subscriber观察者是 Observer的子类。Observable发出一系列事件Subscriber处理这些事件。首先来看一个基本的例子我们如何创建并使用Observable。 Observable.create(new Observable.OnSubscribeString() { Override public void call(Subscriber? super String subscriber) { subscriber.onNext(hello); } }).subscribe(new SubscriberString(){ Override public void onCompleted() {} Override public void onError(Throwable e) { } Override public void onNext(String s) { Log.d(rx-info, s); } });创建Observable的最基本的方法是通过Observable.create() 来进行当有Subscriber通过Observable.subscribe() 方法进行订阅之后Observable就会发射事件注意必须要有订阅者订阅才会发射事件。发射的方式是通过调用 Observable中的 OnSubsribe 类型的成员来实现每个Observable有一个final OnSubscribeT onSubscribe 成员该成员是一个接口后面详细说在 Onsubsribe类型成员中调用 call() 方法注意这个call方法的参数就是 Observable.subscribe() 方法传入的 Subsriber实例。总的一句话就是在Obsubscribe 的 call方法中执行订阅者Subscriber的三个方法 onNext(), onCompleted() 和 onError()。 一开始就是一堆 Observable , Subscribersubscribe() , OnSubscribe 估计看得头晕因此我们需要先来对这些东西有一个了解。这里只列出一个帮助理解的大概。 public class ObservableT {final OnSubscribeT onSubscribe;protected Observable(OnSubscribeT f) {this.onSubscribe f;}public final static T ObservableT create(OnSubscribeT f) {return new ObservableT(hook.onCreate(f));}public interface OnSubscribeT extends Action1Subscriber? super T {// cover for generics insanity}public final Subscription subscribe(Subscriber? super T subscriber) {return Observable.subscribe(subscriber, this);}public interface OperatorR, T extends Func1Subscriber? super R, Subscriber? super T {// cover for generics insanity}
} public interface Action1T extends Action {void call(T t);
} public interface Subscription {void unsubscribe();boolean isUnsubscribed();
}
public interface ObserverT {void onCompleted();void onError(Throwable e);void onNext(T t);
}public abstract class SubscriberT implements ObserverT, Subscription {//...
}通过上面的代码帮助理清楚 Observable, Observer, Subscriber, OnSubsriber, subscribe() 之间的关系。这里额外提一下 Observable.subscribe() 方法有多个重载 Subscription subscribe()
Subscription subscribe(Action1? super T onNext)
Subscription subscribe(Action1? super T onNext, Action1 java.lang .Throwable onError)
Subscription subscribe(Action1? super T onNext, Action1 java.lang .Throwable onError, Action0 onComplete)
Subscription subscribe(Observer? super T observer)
Subscription subscribe(Subscriber? super T subscriber)其它的ActionX 和 FuncX 请大家自行去查阅定义。 介绍了基本的创建Observable和 Observable是怎么发射事件的之后来介绍一下Rxjava的Operator和Operator的原理。 Rxjava的Operator常见的有map, flatMap, concat, merge之类的。这里就不介绍Operator的使用了介绍一下其原理。介绍原理还是来看源码以map为例。 首先看一下使用map的例子 Observable.create(new Observable.OnSubscribeString() {Overridepublic void call(Subscriber? super String subscriber) {subscriber.onNext(hello);}
})
.map(new Func1String, String() {Overridepublic String call(String s) {return s word;}
})
.subscribe(new SubscriberString() {Overridepublic void onCompleted() {}Overridepublic void onError(Throwable e) {}Overridepublic void onNext(String s) {Log.d(info-rx, s);}
});继续来看 map的定义 public final R ObservableR map(Func1? super T, ? extends R func) {return lift(new OperatorMapT, R(func));}简单说一下Func1其中的T表示传入的参数类型R表示方法返回的参数类型。Operator的操作原理最核心的就是lift的实现。 public final R ObservableR lift(final Operator? extends R, ? super T operator) {return new ObservableR(new OnSubscribeR() {Overridepublic void call(Subscriber? super R o) {try {Subscriber? super T st hook.onLift(operator).call(o);try {// new Subscriber created and being subscribed with so onStart itst.onStart();onSubscribe.call(st);} catch (Throwable e) {// localized capture of errors rather than it skipping all operators // and ending up in the try/catch of the subscribe method which then// prevents onErrorResumeNext and other similar approaches to error handlingExceptions.throwIfFatal(e);st.onError(e);}} catch (Throwable e) {Exceptions.throwIfFatal(e);// if the lift function failed all we can do is pass the error to the final Subscriber// as we dont have the operator available to uso.onError(e);}}});}lift方法看起来太过复杂稍作简化 public final R ObservableR lift(final Operator? extends R, ? super T operator) {return new ObservableR(...);
}lift方法实际是产生一个新的 Observable。在map()调用之后我们操作的就是新的Observable对象我们可以把它取名为Observable$2我们这里调用subscribe就是Observable$2.subscribe继续看到subscribe里重要的几个调用 hook.onSubscribeStart(observable, observable.onSubscribe).call(subscriber);
return hook.onSubscribeReturn(subscriber);注意这里的observable是Observable$2也就是说这里的onSubscribe是lift中定义的 回过头来看lift方法中创建新Observable的过程 return new ObservableR(new OnSubscribeR() {Overridepublic void call(Subscriber? super R o) {try {Subscriber? super T st hook.onLift(operator).call(o);try {// new Subscriber created and being subscribed with so onStart itst.onStart();onSubscribe.call(st); //请注意我 这个onSubscribe是原始的OnSubScribe对象} catch (Throwable e) {// localized capture of errors rather than it skipping all operators // and ending up in the try/catch of the subscribe method which then// prevents onErrorResumeNext and other similar approaches to error handlingif (e instanceof OnErrorNotImplementedException) {throw (OnErrorNotImplementedException) e;}st.onError(e);}} catch (Throwable e) {if (e instanceof OnErrorNotImplementedException) {throw (OnErrorNotImplementedException) e;}// if the lift function failed all we can do is pass the error to the final Subscriber// as we dont have the operator available to uso.onError(e);}}
});一定一定要注意这段函数执行的上下文这段函数中的onSubscribe对象指向的是外部类也就是第一个Observable的onSubScribe而不是Observable$2中的onSubscribe接下来看 Subscriber? super T st hook.onLift(operator).call(o);这行代码就是定义operator生成一个经过operator操作过的Subscriber看下OperatorMap这个类中的call方法 Override
public Subscriber? super T call(final Subscriber? super R o) {return new SubscriberT(o) {Overridepublic void onCompleted() {o.onCompleted();}Overridepublic void onError(Throwable e) {o.onError(e);}Overridepublic void onNext(T t) {try {o.onNext(transformer.call(t));} catch (Throwable e) {Exceptions.throwIfFatal(e);onError(OnErrorThrowable.addValueAsLastCause(e, t));}}};
}没错对传入的Subscriber做了一个代理把转换后的值传入。这样就生成了一个代理的Subscriber最后我们最外层的OnSubscribe对象对我们代理的Subscriber进行了调用 Override
public void call(Subscriber? super String subscriber) {//此处的subscriber就是被map包裹(wrapper)后的对象。subscriber.onNext(hello);
}然后这个subscriber传入到内部链式的通知最后通知到我们在subscribe函数中定义的对象。 分析lift的原理其实还是回到了一开始介绍的Observable必须要有订阅者进行订阅才能发射事件。lift方法会产生一个新的Observable并且这个Observable位于原始Observable和后面的Subsriber之间因此lift方法也需要提供一个新的Subscriber来使得新产生的Observable发射事件这个新的Subsriber就是对事件链后方的Subscriber就行包装做一个代理。 详细使用Rxjava可参见 1. 给 Android 开发者的 RxJava 详解 2.Rxjava使用基础合集 转载于:https://www.cnblogs.com/zhuyp1015/p/5215381.html
