1, Add RxJava2 to Android Studio

1. Add in build.Gradle:
compile 'io.reactivex.rxjava2:rxandroid:2.0.1'
compile 'io.reactivex.rxjava2:rxjava:2.1.2'
2. Click synet,
3. Add complete.

2, Simple use of RxJava2

1. Set a scene.
There is a fast food restaurant.
You ordered a fast food and left your address.
Send meals to your house.

2. Write code.

      //Create a fast food restaurant. Observable (observed)
      Observable<String> kuaicandian=Observable.create(new ObservableOnSubscribe<String>() {
          @Override
          public void subscribe(ObservableEmitter<String> e) throws Exception {
              Thread.sleep(6000);
              e.onNext("Fast food (beef noodles)");
              e.onComplete();
          }
      });

        //Create a you. Observer
        Observer<String> observer = new Observer<String>() {
            @Override
            public void onSubscribe(Disposable d) {
                Log.d("RxJava-Start delivering fast food", "subscribe");
            }

            @Override
            public void onNext(String value) {
                Log.d("RxJava-Fast food service", "" + value);
            }

            @Override
            public void onError(Throwable e) {
                Log.d("RxJava-Fast food delivery error", "error");
            }

            @Override
            public void onComplete() {
                Log.d("RxJava-Fast food delivery this task is completed", "complete");
            }
        };

        //Leave your address with the fast food restaurant. Subscribe
        observable.subscribe(observer);

3. Click "key 1", the interface is frozen (beef noodle is being made). After a while, the operation result appears

There is no error, so there are only three lines of information.

4. All codes are as follows:
Interface code:

<?xml version="1.0" encoding="utf-8"?>
 <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
         xmlns:app="http://schemas.android.com/apk/res-auto"
         xmlns:tools="http://schemas.android.com/tools"
         android:layout_width="match_parent"
         android:layout_height="match_parent"
         tools:context="com.example.ls30_rxjava2_1.MainActivity">


         <TextView
         android:id="@+id/tv"
         android:layout_width="match_parent"
             android:layout_height="wrap_content"
             android:text="TextView" />

     <LinearLayout
         android:layout_width="match_parent"
         android:layout_height="match_parent"
         android:gravity="bottom"
         android:orientation="horizontal">

         <Button
             android:id="@+id/bt1"
             android:layout_width="wrap_content"
             android:layout_height="wrap_content"
             android:layout_weight="1"
             android:text="Key 1"
             android:onClick="bt1_onClick"
             />

         <Button
             android:id="@+id/bt2"
             android:layout_width="wrap_content"
             android:layout_height="wrap_content"
             android:layout_weight="1"
             android:text="Key 2"
             android:onClick="bt2_onClick"/>

         <Button
             android:id="@+id/bt3"
             android:layout_width="wrap_content"
             android:layout_height="wrap_content"
             android:layout_weight="1"
             android:text="Key 3"
             android:onClick="bt3_onClick"/>

         <Button
             android:id="@+id/bt4"
             android:layout_width="wrap_content"
             android:layout_height="wrap_content"
             android:layout_weight="1"
             android:text="Key 4"
             android:onClick="bt4_onClick"/>
     </LinearLayout>
     </RelativeLayout>

java code

public class MainActivity extends AppCompatActivity {

  TextView tv;
  @Override
  protected void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.activity_main);
      tv=(TextView) findViewById(R.id.tv);
  }

  public void bt1_onClick(View view) {
      tv.setText("");
      //Create a fast food restaurant. Observable (observed)
      Observable<String> kuaicandian=Observable.create(new ObservableOnSubscribe<String>() {
          @Override
          public void subscribe(ObservableEmitter<String> e) throws Exception {
              Thread.sleep(6000);
              e.onNext("Fast food (beef noodles)");
              e.onComplete();
          }
      });

      Observer<String> wo=new Observer<String>() {
          @Override
          public void onSubscribe(Disposable d) {
              tv.setText(tv.getText()+"RxJava-Start delivering fast food"+"\n");
          }

          @Override
          public void onNext(String s) {
              tv.setText(tv.getText()+"RxJava-Fast food service:"+s+"\n");
          }

          @Override
          public void onError(Throwable e) {
              tv.setText(tv.getText()+"RxJava-Fast food delivery error"+"\n");
          }

          @Override
          public void onComplete() {
              tv.setText(tv.getText()+"RxJava-The fast food is delivered"+"\n");
          }
      };
      //Leave your address with the fast food restaurant. Subscribe
      kuaicandian.subscribe(wo);

  }
  public void bt3_onClick(View view) {
      tv.setText("Press button 3");
  }
    public void bt2_onClick(View view) {
      tv.setText("Press button 2");
  }
  public void bt4_onClick(View view) {
      tv.setText("Click button 4");
  }
}