FragmentManager与FragmentTransaction

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Activity管理Fragment主要依赖于FragmentManager
FragmentManager主要有一下几个功能：
1、使用findFragmentById()或findFragmentByTag()方法来获取指定Fragment。
2、调用popBackStack()方法将Fragment从后台栈中弹出（模拟用户按下BACK按键）。
3、调用addOnBackStackChangeListener()注册一个监听器，用于监听后台栈的变化。
**如果需要添加、删除、替换Fragment，则需要借助FragmentTransaction对象，FragmentTransaction代表Activity对Fragment执行多个改变。

提示：FragmentTransaction也被翻译成Fragment事务。与数据库事务类似的是，数据库事务代表了底层数组的多个更新操作；而Fragment事务代表了Activity对Fragment执行多个改变操作。
可以通过FragmentManager来获得FragmentTransaction:

        FragmentManager fragmentManager=getFragmentManager();        FragmentTransaction fragmentTransaction=fragmentManager.beginTransaction();

每个FragmentTransaction可以包含多个对Fragment的修改，比如包含调用了多个add()、remove()、和replace()操作，最后调用commit()方法提交事务。

Maintivity:

public class MainActivity extends Activity {    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);    }}

LeftFragment:

public class LeftFragment extends Fragment{    private Button btn_1;    private Button btn_2;    private Button btn_3;    private FragmentTransaction fragmentTransaction;    private FragmentManager fragmentManager;    private RightFragment rightFragment;    @Override    public void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        fragmentManager=getFragmentManager();        fragmentTransaction=fragmentManager.beginTransaction();        fragmentTransaction.add(R.id.rightfragment, new RightFragment());        fragmentTransaction.commit();    }    @Override    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {        View view=inflater.inflate(R.layout.left_fragment, container,false);        btn_1=(Button) view.findViewById(R.id.btn_1);        btn_2=(Button) view.findViewById(R.id.btn_2);        btn_1.setOnClickListener(listener);        btn_2.setOnClickListener(listener);        return view;    }    @Override    public void onPause() {        // TODO Auto-generated method stub        super.onPause();    }    private View.OnClickListener listener=new View.OnClickListener() {        public void onClick(View v) {            fragmentTransaction=fragmentManager.beginTransaction();            switch (v.getId()) {            case R.id.btn_1:                fragmentTransaction.replace(R.id.rightfragment, new RightFragment1());                break;            case R.id.btn_2:                fragmentTransaction.replace(R.id.rightfragment, new RightFragment2());                break;            default:                break;            }            fragmentTransaction.commit();               }    };}

RightFragment:

public class RightFragment extends Fragment{    @Override    public void onCreate(Bundle savedInstanceState) {        // TODO Auto-generated method stub        super.onCreate(savedInstanceState);    }    @Override    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {        View view=inflater.inflate(R.layout.right_fragment, container, false);        return view;    }}

RightFragment1:

public class RightFragment1 extends Fragment{    @Override    public void onCreate(Bundle savedInstanceState) {        // TODO Auto-generated method stub        super.onCreate(savedInstanceState);    }    @Override    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {        View view=inflater.inflate(R.layout.right_fragment1, container, false);        return view;    }}

RightFragment2:

public class RightFragment2 extends Fragment{    @Override    public void onCreate(Bundle savedInstanceState) {        // TODO Auto-generated method stub        super.onCreate(savedInstanceState);    }    @Override    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {        View view=inflater.inflate(R.layout.right_fragment2, container, false);        return view;    }}

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