RxJava学习(五)

使用RxJava从多个数据源中加载数据

需求：
1.偶尔的从网络上获取新数据。
2.尽快的恢复数据（通过缓存网络数据的结果）

我们看看用RxJava如何实现

我们给每一个数据源一个Obserable接口，然后通过concat和first这两个操作符来实现。
1.Data(模拟数据源)

public class Data {
    private static final long STALE_MS = 5 * 1000; // Data is stale after 5 seconds

    final String value;

    final long timestamp;

    public Data(String value) {
        this.value = value;
        this.timestamp = System.currentTimeMillis();
    }

    public boolean isUpToDate() {
        return System.currentTimeMillis() - timestamp < STALE_MS;
    }
}

2.Source(定义观察源)

public class Source {

    // Memory cache of data
    private Data memory = null;

    // What's currently "written" on disk
    private Data disk = null;

    // Each "network" response is different
    private int requestNumber = 0;

    // In order to simulate memory being cleared, but data still on disk
    public void clearMemory() {
        System.out.println("Wiping memory...");
        memory = null;
    }
    Observable<Data> memory(){
        Observable<Data> observable = Observable.create(new Observable.OnSubscribe<Data>() {
            @Override
            public void call(Subscriber<? super Data> subscriber) {
                subscriber.onNext(memory);
                subscriber.onCompleted();
            }
        });//使用固定的装欢把Observable进行转换
        return observable.compose(logSource("=====MEMORY"));
    }

    Observable<Data> disk(){
        Observable<Data> observable = Observable.create(new Observable.OnSubscribe<Data>() {
            @Override
            public void call(Subscriber<? super Data> subscriber) {
                subscriber.onNext(disk);
                subscriber.onCompleted();
            }
        });
        return observable.doOnNext(new Action1<Data>() {
            @Override
            public void call(Data data) {
                memory = data;
            }
        }).compose(logSource("=====DISK"));
    }

    Observable<Data> network(){
        Observable<Data> observable = Observable.create(new Observable.OnSubscribe<Data>() {
            @Override
            public void call(Subscriber<? super Data> subscriber) {
                requestNumber++;
                subscriber.onNext(new Data("Server Response #" + requestNumber));
                subscriber.onCompleted();
            }
        });
        observable.doOnNext(new Action1<Data>() {
            @Override
            public void call(Data data) {
                memory = data;
                disk = data;
            }
        });
        return observable.compose(logSource("========NETWORK"));
    }

    Observable.Transformer<Data,Data> logSource(final String resource){
        return new Observable.Transformer<Data, Data>() {
            @Override
            public Observable<Data> call(Observable<Data> dataObservable) {
                return dataObservable.doOnNext(new Action1<Data>() {
                    @Override
                    public void call(Data data) {
                        if (data == null) {
                            System.out.println(resource + " does not have any data.");
                        }
                        else if (!data.isUpToDate()) {
                            System.out.println(resource + " has stale data.");
                        }
                        else {
                            System.out.println(resource + " has the data you are looking for!");
                        }
                    }
                });
            }
        };
    }
}

3.测试类

public class MainActivity extends AppCompatActivity {
    Source mSource = new Source();
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        //concat:按顺序排列Observerable对象，
        final Observable<Data> observable = Observable.concat(
                mSource.memory(),
                mSource.disk(),//first,返回一个Observable对象，只发射第一个数据，并且进行筛选
                mSource.network()).
                first(new Func1<Data, Boolean>() {
            @Override
            public Boolean call(Data data) {
                //过滤作用，只需要不为空并且未过时的数据
                return data!=null&&data.isUpToDate();
            }
        });
        //每秒请求最新数据，每秒订阅Observable，获取最新数据
        Observable.interval(1, TimeUnit.SECONDS).flatMap(new Func1<Long, Observable<Data>>() {
            @Override
            public Observable<Data> call(Long aLong) {
                return observable;
            }
        }).subscribe(new Action1<Data>() {
            @Override
            public void call(Data data) {
                System.out.println("＝＝＝＝Received: " + data.value);
            }
        });
        //每3秒清除一次内存
        Observable.interval(3,TimeUnit.SECONDS).subscribe(new Action1<Long>() {
            @Override
            public void call(Long aLong) {
                mSource.clearMemory();
            }
        });
//
        sleep(15 * 1000);
    }
    static void sleep(long millis) {
        try {
            Thread.sleep(millis);
        }
        catch (InterruptedException e) {
            // Ignore
        }
    }
}

我们看看最终的运行效果

最后给出代码的下载地址
​点此下载源码​​