安卓开发_浅谈Fragment之事务添加Fragment对象

我们都知道给一个activity动态添加fragment的时候 有下面几种添加方式

看一下布局文件

 <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
     xmlns:tools="http://schemas.android.com/tools"
     android:layout_width="match_parent"
     android:layout_height="match_parent"
     android:orientation="vertical"
     >

     <FrameLayout
         android:layout_width="wrap_content"
         android:layout_height="100dp"
         android:id="@+id/show_fragment"
         ></FrameLayout>

 </LinearLayout>

效果图:

一个帧布局动态显示Fragment对象,

1、

 package com.xqx_backfragment;

 import android.app.Activity;
 import android.app.FragmentManager;
 import android.app.FragmentTransaction;
 import android.os.Bundle;
 import android.view.View;
 import android.view.View.OnClickListener;
 import android.widget.Button;

 public class MainActivity extends Activity {

     private Button btn_new;
     private Button btn_back;
     @Override
     protected void onCreate(Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
         setContentView(R.layout.activity_main);
         btn_new  = (Button) findViewById(R.id.newfragment);
         btn_back = (Button) findViewById(R.id.backfragment);
         //新建一个新的fragment
         btn_new.setOnClickListener(new OnClickListener() {

             @Override
             public void onClick(View v) {
                 // TODO Auto-generated method stub
                 //创建管理者对象
                 FragmentManager manager = getFragmentManager();
                 //创建事务对象
                 FragmentTransaction action = manager.beginTransaction();
                 MyFragment fragment = new MyFragment();
                 action.add(R.id.show_fragment, fragment);
                 action.commit();

 //                MyFragment fragment = new MyFragment();
 //                action.add(R.id.show_fragment, fragment);
 //                action.addToBackStack(null);
 //                action.commit();
             }
         });

         //返回
         btn_back.setOnClickListener(new OnClickListener() {

             @Override
             public void onClick(View v) {
                 // TODO Auto-generated method stub
                 onBackPressed();
             }
         });
     }

 }

add

 //创建管理者对象
                 FragmentManager manager = getFragmentManager();
                 //创建事务对象
                 FragmentTransaction action = manager.beginTransaction();
                 MyFragment fragment = new MyFragment();
                 action.add(R.id.show_fragment, fragment);
                 action.commit();

每次点击新建按钮，都执行上面一段代码，也就是新建一个Fragment对象并加入到事务中，原来的fragment效果被覆盖，只显示最后加入事务的fragment对象，但是此时存在多个fragment对象，之前加入事务的fragment对象都一直存在

点击返回按钮销毁activity 退出activity

2、

 package com.xqx_backfragment;

 import android.app.Activity;
 import android.app.FragmentManager;
 import android.app.FragmentTransaction;
 import android.os.Bundle;
 import android.view.View;
 import android.view.View.OnClickListener;
 import android.widget.Button;

 public class MainActivity extends Activity {

     private Button btn_new;
     private Button btn_back;
     @Override
     protected void onCreate(Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
         setContentView(R.layout.activity_main);
         btn_new  = (Button) findViewById(R.id.newfragment);
         btn_back = (Button) findViewById(R.id.backfragment);
         //新建一个新的fragment
         btn_new.setOnClickListener(new OnClickListener() {

             @Override
             public void onClick(View v) {
                 // TODO Auto-generated method stub
                 //创建管理者对象
                 FragmentManager manager = getFragmentManager();
                 //创建事务对象
                 FragmentTransaction action = manager.beginTransaction();

                 action.replace(R.id.show_fragment, fragment);
                 action.commit();

             }
         });

         //返回
         btn_back.setOnClickListener(new OnClickListener() {

             @Override
             public void onClick(View v) {
                 // TODO Auto-generated method stub
                 onBackPressed();
             }
         });
     }

 }

replace

 //创建管理者对象
                 FragmentManager manager = getFragmentManager();
                 //创建事务对象
                 FragmentTransaction action = manager.beginTransaction();
                 MyFragment fragment = new MyFragment();
                 action.replace(R.id.show_fragment, fragment);
                 action.commit();

每次点击新建按钮，都执行上面一段代码，也就是新建一个Fragment对象并加入到事务中，并且替代原来存在的fragment对象，这种情况下R.id.show_fragment视图上始终只有一个fragment对象

点击返回按钮销毁activity 退出activity

3、

 package com.xqx_backfragment;

 import android.app.Activity;
 import android.app.FragmentManager;
 import android.app.FragmentTransaction;
 import android.os.Bundle;
 import android.view.View;
 import android.view.View.OnClickListener;
 import android.widget.Button;

 public class MainActivity extends Activity {

     private Button btn_new;
     private Button btn_back;
     @Override
     protected void onCreate(Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
         setContentView(R.layout.activity_main);
         btn_new  = (Button) findViewById(R.id.newfragment);
         btn_back = (Button) findViewById(R.id.backfragment);
         //新建一个新的fragment
         btn_new.setOnClickListener(new OnClickListener() {

             @Override
             public void onClick(View v) {
                 // TODO Auto-generated method stub
                 //创建管理者对象
                 FragmentManager manager = getFragmentManager();
                 //创建事务对象
                 FragmentTransaction action = manager.beginTransaction();

                 MyFragment fragment = new MyFragment();
                 action.add(R.id.show_fragment, fragment);
                 action.addToBackStack(null);
                 action.commit();

             }
         });

         //返回
         btn_back.setOnClickListener(new OnClickListener() {

             @Override
             public void onClick(View v) {
                 // TODO Auto-generated method stub
                 onBackPressed();
             }
         });
     }

 }

addToBackStack

 //创建管理者对象
                 FragmentManager manager = getFragmentManager();
                 //创建事务对象
                 FragmentTransaction action = manager.beginTransaction();

                 MyFragment fragment = new MyFragment();
                 action.add(R.id.show_fragment, fragment);
                 action.addToBackStack(null);
                 action.commit();

每次点击新建按钮，都执行上面一段代码，也就是新建一个Fragment对象并加入到事务中，并将对象加入到回退栈中显示出新的fragment效果图

点击返回按钮显示当前fragment之前的fragment效果图  直到没有fragment对象时activity销毁退出

----------------------------------------------------------------------------------------------------------------------------------------

根据需求选择上述三种事务添加fragment对象的方法。

注意：

1、每次添加fragment对象都要将事务提交才有效果（action.commit()） ，下面情况没有事务提交 则fragment对象没有成功加入事务

 //创建管理者对象
                 FragmentManager manager = getFragmentManager();
                 //创建事务对象
                 FragmentTransaction action = manager.beginTransaction();
                 MyFragment fragment = new MyFragment();
                 action.add(R.id.show_fragment, fragment);

正确写法：

 //创建管理者对象
                 FragmentManager manager = getFragmentManager();
                 //创建事务对象
                 FragmentTransaction action = manager.beginTransaction();
                 MyFragment fragment = new MyFragment();
                 action.add(R.id.show_fragment, fragment);
7                 action.commit();

2、每次事务提交之前都要有这个事务对象，下面情况action.commit()之后 不能继续action.commit()

 //创建管理者对象
                 FragmentManager manager = getFragmentManager();
                 //创建事务对象
                 FragmentTransaction action = manager.beginTransaction();
                 MyFragment fragment = new MyFragment();
                 action.add(R.id.show_fragment, fragment);
                 action.commit();
                 MyFragment fragment1 = new MyFragment();
                 action.add(R.id.show_fragment, fragment1);
                 action.commit();

正确写法：

 //创建管理者对象
                 FragmentManager manager = getFragmentManager();
                 //创建事务对象
                 FragmentTransaction action = manager.beginTransaction();
                 MyFragment fragment = new MyFragment();
                 action.add(R.id.show_fragment, fragment);
                 action.addToBackStack(null);
                 action.commit();

                 action = manager.beginTransaction();
                 MyFragment fragment1 = new MyFragment();
                 action.add(R.id.show_fragment, fragment1);
                 action.addToBackStack(null);
                 action.commit();