RxJava concat operator processing multiple data sources

Overview

From the Concatmap operation we know that the concat operator is definitely also ordered, and the concat operator is to receive a number of observables, the emission data is ordered, will not cross.

Using the example

Example One

The following example uses the concat operator to implement a multi-data source, such as a product detail needs to display information about a product, artist information, a product similar to that item, and may require access to three interfaces. You can use the concat operator at this time.

Seller Information

private Observable<Object> sellerInfo = Observable.create(new Observable.OnSubscribe<Object>() {        @Override        publicvoidcallsuper Object> subscriber) {            Seller d = goodsApi.getSeller();            ifnull) {                subscriber.onNext(d);            }            subscriber.onCompleted();        }    }).subscribeOn(Schedulers.io());

Product Information

private Observable<Object> goodsInfo = Observable.create(new Observable.OnSubscribe<Object>() {        @Override        publicvoidcallsuper Object> subscriber) {            Goods d = goodsApi.getGoodInfo();            ifnull) {                subscriber.onNext(d);            }            subscriber.onCompleted();        }    }).subscribeOn(Schedulers.io());

Similar works recommended

private Observable<Object> relateGoods = Observable.create(new Observable.OnSubscribe<Object>() {        @Override        publicvoidcallsuper Object> subscriber) {            List<Goods> d = goodsApi.getRelateGoods();            ifnull) {                subscriber.onNext(d);            }            subscriber.onCompleted();        }    }).subscribeOn(Schedulers.io());

Observable.concat (Sellerinfo, Goodsinfo, Relategoods). Observeon (Androidschedulers.mainthread ()) . Subscribe (NewAction1<object> () {@Override                             Public void Pager(Object s) {Printlog (Tvlogs,"Getting data from", s);//push data to UI                                //for example:if (S instanceof User)}                        },NewAction1<throwable> () {@Override                             Public void Pager(Throwable throwable)                                {Throwable.printstacktrace (); Printlog (Tvlogs,"Error:", Throwable.getmessage ()); }                        });

Why generics are set to object, because Observable.concat only accepts parameters of the same generic type.

May be asked to obtain the product information when there is no way to pass the parameters AH (such as Product ID), the outer bread layer method can be, the method parameter is Goodid.

Example Two

The cache is checked using the concat operator, such as: Memory cache, local cache, network, and that layer has data immediately returned.

Use an array to represent three data sources:

String  data[] = {null, null, "network"};//String  data[] = {null, "disk", "network"};//String  data[] = {"memory", null, "network"};//String  data[] = {"memory", "disk",null};//String  data[] = {"memory", "disk", "network"};

Memory Cache

  private Observable<String> memorySource = Observable.create(new Observable.OnSubscribe<String>() {        @Override        publicvoidcallsuper String> subscriber) {            String d = data[0];            """----start check memory data. value is null? "null));            ifnull) {                subscriber.onNext(d);            }            subscriber.onCompleted();        }    });

Local cache

private  observable< string> Disksource = observable.create (new  observable.onsubscribe<string > () { @Override  public  void  call  (subscriber<? super             string> subscriber) {String d = data[1 ]; Printlog (tvlogs, ,  "----start check disk data. Value is NULL?            " + (d = = null )); if  (d! = null )            {Subscriber.onnext (d);        } subscriber.oncompleted (); }}). Subscribeon (Schedulers.io ());  

Network

private  observable< string> Networksource = observable.create (new  observable.onsubscribe<  String> () { @Override  public  void  call  (subscriber<? super             string> subscriber) {String d = data[2 ]; Printlog (tvlogs, ,  "----start check network data. Value is NULL?            " + (d = = null )); if  (d! = null )            {Subscriber.onnext (d);        } subscriber.oncompleted (); }}). Subscribeon (Schedulers.io ());  

From Example 1 we know that the concat will be requested by three data sources. How to make which layer has data to use which layer, then do not go behind the logic.

This effect can be achieved with the first () operator.

Observable.concat (Memorysource, Disksource, Networksource). First (). Observe On (Androidschedulers.mainthread ()). Subscribe (NewAction1<string> () {@Override                             Public void Pager(String s) {Printlog (Tvlogs,"Getting data from", s); }                        },NewAction1<throwable> () {@Override                             Public void Pager(Throwable throwable)                                {Throwable.printstacktrace (); Printlog (Tvlogs,"Error:", Throwable.getmessage ()); }                        });

It should be noted that if Memorysource, Disksource, networksource return null, then an exception will be reported:
Java.util.NoSuchElementException:Sequence contains no elements ...

You can use the Takefirst operation, which does not report an exception even if there is no data.

Observable.concat (Memorysource, Disksource, Networksource)//first (), if no data from observables would cause exception:                        //java.util.nosuchelementexception:sequence contains no elements                        //takefirst-no exception. Takefirst (NewFunc1<string, boolean> () {@Override                             PublicBooleanPager(String s) {returns! =NULL; }}). Observeon (Androidschedulers.mainthread ()). Subs Cribe (NewAction1<string> () {@Override                             Public void Pager(String s) {Printlog (Tvlogs,"Getting data from", s); }                        },NewAction1<throwable> () {@Override                             Public void Pager(Throwable throwable)                                {Throwable.printstacktrace (); Printlog (Tvlogs,"Error:", Throwable.getmessage ()); }                        });

Transferred from: http://blog.csdn.net/johnny901114/article/details/51568562

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RxJava concat operator processing multiple data sources