RX转换符 map
map()函数接受一个Func1类型的参数(就像这样map(Func1 func)),然后吧这个Func1应用到每一个由Observable发射的值上，将发射的只转换为我们期望的值
用法，Observable.just(
举个列子，现在我们传入的Integer类型数据，但是要对这些数据做处理，成String类型的数据，例子代码如下
Observable.just(1,2,3,4).map(new Function() {
@Override
public String apply(Integer arg0) throws Exception {
// TODO Auto-generated method stub
return ""+arg0;
}
}).subscribe(new Observer() {
@Override
public void onSubscribe(Disposable disposable) {
}
@Override
public void onNext(String t) {
System.out.println("onNext:"+t);
}
@Override
public void onError(Throwable e) {
// TODO Auto-generated method stub
}
@Override
public void onComplete() {
// TODO Auto-generated method stub
System.out.println("onComplete");
}
});
打印结果如下
onNext:1
onNext:2
onNext:3
onNext:4
onComplete
确实奏效了
现在查看源码
Observavle的just方法，这里调用了fromArray方法
public static Observable just(T item1, T item2, T item3, T item4) {
ObjectHelper.requireNonNull(item1, "The first item is null");
ObjectHelper.requireNonNull(item2, "The second item is null");
ObjectHelper.requireNonNull(item3, "The third item is null");
ObjectHelper.requireNonNull(item4, "The fourth item is null");
return fromArray(new Object[]{item1, item2, item3, item4});
}
查看fromArray方法，里面封装成一个ObservableFromArray类
public static Observable fromArray(T... items) {
ObjectHelper.requireNonNull(items, "items is null");
return items.length == 0?empty():(items.length == 1?just(items[0]):RxJavaPlugins.onAssembly(new ObservableFromArray(items)));
}
继续map方法，把ObservableFromArray又封装到一个ObservableMap类
public final Observable map(Function mapper) {
ObjectHelper.requireNonNull(mapper, "mapper is null");
return RxJavaPlugins.onAssembly(new ObservableMap(this, mapper));
}
最后subscribe方法
public final void subscribe(Observer observer) {
ObjectHelper.requireNonNull(observer, "observer is null");
try {
observer = RxJavaPlugins.onSubscribe(this, observer);
ObjectHelper.requireNonNull(observer, "Plugin returned null Observer");
this.subscribeActual(observer);
} catch (NullPointerException var4) {
throw var4;
} catch (Throwable var5) {
Exceptions.throwIfFatal(var5);
RxJavaPlugins.onError(var5);
NullPointerException npe = new NullPointerException("Actually not, but can't throw other exceptions due to RS");
npe.initCause(var5);
throw npe;
}
}
也就是说封装的顺序ObservableFromArray->ObservableMap
而ObservableMap 的subscribeActual方法，调用了Observavle的subscribe方法，我们都知道，Observavle会调用子类实现的subscribeActual方法，
ObservableMap 的subscribeActual方法
public void subscribeActual(Observer t) {
this.source.subscribe(new ObservableMap.MapObserver(t, this.function));
}
而这里的source是ObservableFromArray类，因此我们查看ObservableFromArray类的subscribeActual方法
ObservableFromArray类的subscribeActual方法。这里调用了传入对象的onSubscribe方法，我们传入的是ObservableMap.MapObserver对象
public void subscribeActual(Observer s) {
ObservableFromArray.FromArrayDisposable d = new ObservableFromArray.FromArrayDisposable(s, this.array);
s.onSubscribe(d);
if(!d.fusionMode) {
d.run();
}
}
调用ObservableMap.MapObserver对象的onSubscribe方法，ObservableMap.MapObserver对象的onSubscribe又会调用我们传入的Observer
查看run方法，里面这个array就行just方法传入进来的数组，这里遍历了数组，因为构造器ObservableFromArray.FromArrayDisposable(s, this.array)的第一个参数传入的是ObservableMap.MapObserver对象，所以这里依次调用了ObservableMap.MapObserver的onNext方法。调用完onNext方法
ObservableFromArray.FromArrayDisposable的run方法
void run() {
T[] a = this.array;
int n = a.length;
for(int i = 0; i < n && !this.isDisposed(); ++i) {
T value = a[i];
if(value == null) {
this.actual.onError(new NullPointerException("The " + i + "th element is null"));
return;
}
this.actual.onNext(value);
}
if(!this.isDisposed()) {
this.actual.onComplete();
}
}
而ObservableMap.MapObserver构造器里面传入的是我们创建的new Function
因此这里的mapper调用的就是我们Function对象里面的apply方法，这里就是把Integer类型的数据转换为String类型的数据，并且转换后的对象作为参数，传入subscribe(new Observer
ObservableMap.MapObserver的onNext方法
public void onNext(T t) {
if(!this.done) {
if(this.sourceMode != 0) {
this.actual.onNext((Object)null);
} else {
Object v;
try {
v = ObjectHelper.requireNonNull(this.mapper.apply(t), "The mapper function returned a null value.");
} catch (Throwable var4) {
this.fail(var4);
return;
}
this.actual.onNext(v);
}
}
}
继续查看run方法，调用完onNext方法，后调用了onComplete方法
ObservableFromArray.FromArrayDisposable的run方法
void run() {
T[] a = this.array;
int n = a.length;
for(int i = 0; i < n && !this.isDisposed(); ++i) {
T value = a[i];
if(value == null) {
this.actual.onError(new NullPointerException("The " + i + "th element is null"));
return;
}
this.actual.onNext(value);
}
if(!this.isDisposed()) {
this.actual.onComplete();
}
}