// 首先需要创建启动的Activity对应的Intent
Intent intent = new Intent(MainActivity.this, TwoActivity.class);

// 启动Activity
startActivity(Intent intent);
startActivityForResult(Intent intent, int requestCode); // requestCode：请求码
//startActivityForResult方法以指定的请求码启动Activity，并通过重写onActivityResult方法获取返回的结果。

// 关闭Activity
finish();
finishActivity(int requestCode);
// finishActivity方法结束以startActivityForResult方法启动的Activity。

public class MainActivity extends Activity {
  Button bn;
  @Override
  public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);
    // 获取界面上的组件
    ...
    // 绑定事件监听器
    bn.setOnClickListener(new OnClickListener() {
      @Override
      public void onClick(View view) {
        Intent intent = new Intent(MainActivity.this, TwoActivity.class);
        startActivityForResult(intent, 0); // 0是请求码，用于标识该请求
      }
    });
  }
  @Override
  public void onActivityResult(int requestCode, int resultCode, Intent intent) {
    // 处理特定的结果
    if (requestCode == 0 && resultCode == 0) {
      // 取出Intent里的Extras数据
      Bundle data = intent.getExtras();
      // 取出Bundle中的数据
      String result = data.getString("test");
      Toast.makeText(getApplicationContext(), result, 0).show();
    }
  }
}

// 获取启动该Activity之前的Activity对应的Intent
Intent intent = getIntent();
intent.putExtra("test", "test");
// 设置该SelectActivity的结果码，并设置结束之后退回的Activity
SelectCityActivity.this.setResult(0, intent);
// 结束TwoActivity
TwoActivity.this.finish();

intent.putExtras(Bundle data); // 向Intent放入数据包
intent.putExtras(String name, Xxx value); // 向Intent中按key-value对的形式放入数据
intent.getExtras(); // 取出Intent中携带的数据包
intent.getXxxExtras(String name); //从Intent中按key取出指定类型的数据

Bundle bundle = new Bundle(); // 首先创建一个Bundle对象
bundle.putXxx(String key, Xxx data); // 向Bundle中放入数据
bundle.putSerializable(String key, Serializable data); // 向Bundle中放入一个可序列化的对象（即实现了java.io.Serializable接口）
bundle.getXxx(String key); // 从Bundle中取出数据
bundle.getSerializable(String key); // 从Bundle中取出一个可序列化的对象

// 重写该方法，该方法返回的View将作为Fragment显示的组件
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
  // 加载/res/layout/目录下的fragment.xml布局文件
  View view = inflater.inflate(R.layout.fragment, container, false);
  TextView name = (TextView)view.findViewById(R.id.name));
  ...
  return view;
}

public class MyFragment extends Fragment  { 
  @Override 
  public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { 
    return inflater.inflate(R.layout.fragment_my, container, false); 
  } 
}
public class TwoFragment extends Fragment  { 
  @Override 
  public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { 
    return inflater.inflate(R.layout.fragment_two, container, false); 
  } 
}

// 设置默认的Fragment
FragmentManager fm = getFragmentManager(); 
FragmentTransaction transaction = fm.beginTransaction(); 
myFragment = new MyFragment(); 
transaction.replace(R.id.fl, myFragment); 
transaction.commit();

@Override 
public void onClick(View v) { 
  FragmentManager fm = getFragmentManager(); 
  // 开启Fragment事务 
  FragmentTransaction transaction = fm.beginTransaction(); 
  twoFragment = new TwoFragment(); 
  // 使用当前Fragment的布局替代fl的控件 
  transaction.replace(R.id.fl, twoFragment); 
  // transaction.addToBackStack(); // 将事物添加到back栈，允许用户按BACK按键返回到替换Fragment之前的状态
  // 事务提交 
  transaction.commit(); 
}