（1）combineLatest基礎(chǔ)

RxJava的combineLatest()函數(shù)有點(diǎn)像zip()函數(shù)的特殊形式。

• zip()作用于最近未打包的兩個(gè)Observables揖闸，其中一個(gè)Observable發(fā)射數(shù)據(jù)項(xiàng)后揍堕，組合所有Observable最早一個(gè)未被組合的數(shù)據(jù)項(xiàng)相反；

• combineLatest()作用于最近發(fā)射的數(shù)據(jù)項(xiàng)汤纸，在其中一個(gè)Observable發(fā)射數(shù)據(jù)項(xiàng)后鹤啡，組合所有Observable所發(fā)射的最后一個(gè)數(shù)據(jù)項(xiàng)（前提是所有的Observable都至少發(fā)射過(guò)一個(gè)數(shù)據(jù)項(xiàng)）,如下圖所示;
  

  combineLatest.png
  
  其原理即：如果Observable1發(fā)射了1,接著Observable2發(fā)射了A，combineLatest()將會(huì)處理1和A蹲嚣，組合成1A递瑰；而Observable1發(fā)射了2，此時(shí)Observable2只發(fā)射了A隙畜，所以combineLatest()將處理2和A抖部，組合成2A；待Observable2發(fā)射了B時(shí)议惰，此時(shí)Observable1發(fā)射的最后一個(gè)數(shù)據(jù)是2慎颗，combineLatest()將處理2和B，組合成2B言询；以此類(lèi)推組合成2C俯萎，2D，3D等等运杭。

（2）combineLatest項(xiàng)目實(shí)戰(zhàn)

• EditText表單的校驗(yàn)
  這個(gè)示例中夫啊，包含用戶(hù)名、密碼輸入框辆憔，它們的長(zhǎng)度要求分別為2~8 和 4~16撇眯，如果兩者都正確报嵌，那么登錄按鈕的文案變?yōu)椤暗卿洝保駝t顯示“用戶(hù)名或密碼無(wú)效”熊榛。

public class CombineLatestActivity extends AppCompatActivity {
   private EditText mEtName;
   private EditText mEtPassword;
   private Button mBtLogin;
   private PublishSubject<String> mNameSubject;
   private PublishSubject<String> mPasswordSubject;
   private CompositeDisposable mCompositeDisposable;

   @Override
   protected void onCreate(Bundle savedInstanceState) {
       super.onCreate(savedInstanceState);
       setContentView(R.layout.activity_combine_latest);
       mEtName = (EditText) findViewById(R.id.et_name);
       mEtPassword = (EditText) findViewById(R.id.et_password);
       mBtLogin = (Button) findViewById(R.id.bt_login);
       //創(chuàng)建Subject
       mNameSubject = PublishSubject.create();
       mPasswordSubject = PublishSubject.create();
      //添加EditText輸入監(jiān)聽(tīng)
       mEtName.addTextChangedListener(new EditTextMonitor(mNameSubject));
       mEtPassword.addTextChangedListener(new EditTextMonitor(mPasswordSubject));
       //創(chuàng)建被觀(guān)察者
       Observable<Boolean> observable = Observable.combineLatest(mNameSubject, mPasswordSubject, new BiFunction<String, String, Boolean>() {
           @Override
           public Boolean apply(String name, String password) throws Exception {
               int nameLen = name.length();
               int passwordLen = password.length();
               return nameLen >= 2 && nameLen <= 8 && passwordLen >= 4 && passwordLen <= 16;
           }
       });
       //創(chuàng)建觀(guān)察者
       DisposableObserver<Boolean> disposable = new DisposableObserver<Boolean>() {
           @Override
           public void onNext(Boolean value) {
               mBtLogin.setText(value ? "登錄" : "用戶(hù)名或密碼無(wú)效");
           }
           @Override
           public void onError(Throwable e) {
           }
           @Override
           public void onComplete() {
           }
       };
       observable.subscribe(disposable);
       mCompositeDisposable = new CompositeDisposable();
       mCompositeDisposable.add(disposable);
   }

    private class EditTextMonitor implements TextWatcher {
        private PublishSubject<String> mPublishSubject;
        EditTextMonitor(PublishSubject<String> publishSubject) {
            mPublishSubject = publishSubject;
        }

        @Override
        public void beforeTextChanged(CharSequence s, int start, int count, int after) {
        }

        @Override
        public void onTextChanged(CharSequence s, int start, int before, int count) {
        }

        @Override
        public void afterTextChanged(Editable s) {
            //發(fā)射數(shù)據(jù)
            mPublishSubject.onNext(s.toString());
        }
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        mCompositeDisposable.clear();
    }
}

• 需求-對(duì)A對(duì)象上的某個(gè)List屬性進(jìn)行RxJava操作, 然后把操作的結(jié)果再重新賦給原來(lái)的A對(duì)象

比如返回一個(gè)用戶(hù)信息User, 里面有List屬性表示他的好友, 但好友的信息只有id, 需要再次通過(guò)id獲取好友具體信息

//獲取用戶(hù)信息
userApi.fetchUserInfo()
        .flatMap(new Func1<User, Observable<User>>() {
            @Override
            public Observable<User> call(User user) {
                printLog(tvLogs, "----fetch a user---- \n", getUserString(user))
                return fetchFriendsInfo(user);
            }
        })
        .subscribeOn(Schedulers.io())
        .observeOn(AndroidSchedulers.mainThread())
        .subscribe(new Action1<User>() {
            @Override
            public void call(User user) {
                printLog(tvLogs, "----process his friends by id---- \n", getUserString(user));
            }
        }, new Action1<Throwable>() {
            @Override
            public void call(Throwable throwable) {
                throwable.printStackTrace();
            }
        });

獲取好友信息并組合

//這個(gè)方法才是實(shí)現(xiàn)的核心
private Observable<User> fetchFriendsInfo(User user) {
    
    //保存User的數(shù)據(jù)
    Observable<User> observableUser = Observable.just(user);
    
    //對(duì)User的好友列表進(jìn)行單獨(dú)處理
    Observable<List<User>> observableUsers = Observable.from(user.getFriends())
            .flatMap(new Func1<User, Observable<User>>() {
                @Override
                public Observable<User> call(User user) {
                    //根據(jù)好友ID獲取更完整的信息
                    return userApi.fetchUserInfo(user.getId() + "");
                }
            })
            .toList();

    //對(duì)用戶(hù)User信息和他的好友信息進(jìn)行合并.
    return Observable.combineLatest(observableUser, observableUsers, new Func2<User, List<User>, User>() {
        @Override
        public User call(User user, List<User> users) {
            user.setFriends(users);
            return user;
        }
    });
}

上面大致的意思就是把User信息分為兩個(gè)部分:一部分是用戶(hù)信(Observable<User>), 一部分是好友列表(Observable<List<User>>)信息 锚国，然后把兩個(gè)最終數(shù)據(jù)進(jìn)行組合