這裡不用Intent傳值，主要簡單介紹下interface的使用

效果如下：

首先新建兩個頁面MainActivity和HomeActivity,佈局很簡單，TextView和Button，看也看出來了，不多說了

接著建立一個觀察者介面：

public interface Watcher {
    void update(String str);
}

然後是被觀察者：

public interface Watched {
    public void addWatcher(Watcher wtcher);
    public void notifyWatcher(String str);
 
}

然後宣告具體的被觀察者：

public class ConcreateWatched implements Watched {
    private List<Watcher> list = new ArrayList<>();
@Override
public void addWatcher(Watcher watcher) {
        list.add(watcher);
}

    @Override
public void notifyWatcher(String str) {
        for (Watcher watcher : list
 
) {
            watcher.update(str);
}
    }
}

緊接著，宣告具體的觀察者，也就是我們的MainActivity:

public class MainActivity extends AppCompatActivity implements Watcher{
    private static final String TAG = "TAG";
@BindView(R.id.tv_first)
    TextView tvFirst;
   public static String text = "資料：";
@Override
protected void 
 
onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
ButterKnife.bind(this);
}

    @OnClick(R.id.btn_firstJump)
    public void onViewClicked() {
        Intent intent = new Intent(this,HomeActivity.class);
startActivity(intent);
}


    @Override
public void update(String str) {
        text = str;
}

    @Override
protected void onResume() {
        super.onResume();
Log.e(TAG, "onResume: " );
tvFirst.setText(text);
}



    private long exitTime = 0;//點選2次返回，退出程式
//點選兩次退出
@Override
public boolean onKeyDown(int keyCode, KeyEvent event) {
        if (keyCode == KeyEvent.KEYCODE_BACK
&& event.getAction() == KeyEvent.ACTION_DOWN) {
            if ((System.currentTimeMillis() - exitTime) > 2000) {//兩秒內再次點選返回則退出
Toast.makeText(getApplicationContext(), "再按一次退出程式",
Toast.LENGTH_SHORT).show();
exitTime = System.currentTimeMillis();
} else {
                System.exit(0);
}
            return true;
}

        return super.onKeyDown(keyCode, event);
}
}

最後在HomeActivity裡回撥介面就可以了：

public class HomeActivity extends AppCompatActivity {
    Watched watched;
@Override
protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
setContentView(R.layout.activity_home);
ButterKnife.bind(this);
watched = new ConcreateWatched();
Watcher watcher = new MainActivity();
watched.addWatcher(watcher);
watched.notifyWatcher("資料：我是第二個頁面的資料");
}

    @OnClick(R.id.btn_return)
    public void onViewClicked() {
        finish();
}
}

這裡只是簡單介紹介面的用法，一般用在Activity上點選，然後fragment某個控價發生變化時可以用，那個時候intent不能用了吧！

僅供參考，有不對的歡迎提出。