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

 1 <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
 2     xmlns:tools="http://schemas.android.com/tools"
 3     android:layout_width="match_parent"
 4     android:layout_height="match_parent"
 5     android:orientation="vertical"
 6     >
 7 
 8     <FrameLayout 
 9         android:layout_width="wrap_content"
10         android:layout_height="100dp"
11         android:id="@+id/show_fragment"
12         ></FrameLayout>
13     
14 </LinearLayout>

效果图:

一个帧布局动态显示Fragment对象,

1、

 1 package com.xqx_backfragment;
 2 
 3 import android.app.Activity;
 4 import android.app.FragmentManager;
 5 import android.app.FragmentTransaction;
 6 import android.os.Bundle;
 7 import android.view.View;
 8 import android.view.View.OnClickListener;
 9 import android.widget.Button;
10 
11 public class MainActivity extends Activity {
12     
13     private Button btn_new;
14     private Button btn_back;
15     @Override
16     protected void onCreate(Bundle savedInstanceState) {
17         super.onCreate(savedInstanceState);
18         setContentView(R.layout.activity_main);
19         btn_new  = (Button) findViewById(R.id.newfragment);
20         btn_back = (Button) findViewById(R.id.backfragment);
21         //新建一个新的fragment
22         btn_new.setOnClickListener(new OnClickListener() {
23             
24             @Override
25             public void onClick(View v) {
26                 // TODO Auto-generated method stub
27                 //创建管理者对象
28                 FragmentManager manager = getFragmentManager();
29                 //创建事务对象
30                 FragmentTransaction action = manager.beginTransaction();            
31                 MyFragment fragment = new MyFragment();
32                 action.add(R.id.show_fragment, fragment);
33                 action.commit();
34                 
35 //                MyFragment fragment = new MyFragment();
36 //                action.add(R.id.show_fragment, fragment);
37 //                action.addToBackStack(null);
38 //                action.commit();
39             }
40         });
41         
42         //返回
43         btn_back.setOnClickListener(new OnClickListener() {
44             
45             @Override
46             public void onClick(View v) {
47                 // TODO Auto-generated method stub
48                 onBackPressed();
49             }
50         });
51     }
52     
53     
54 
55 }

1 //创建管理者对象
2                 FragmentManager manager = getFragmentManager();
3                 //创建事务对象
4                 FragmentTransaction action = manager.beginTransaction();            
5                 MyFragment fragment = new MyFragment();
6                 action.add(R.id.show_fragment, fragment);
7                 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、

 1 package com.xqx_backfragment;
 2 
 3 import android.app.Activity;
 4 import android.app.FragmentManager;
 5 import android.app.FragmentTransaction;
 6 import android.os.Bundle;
 7 import android.view.View;
 8 import android.view.View.OnClickListener;
 9 import android.widget.Button;
10 
11 public class MainActivity extends Activity {
12     
13     private Button btn_new;
14     private Button btn_back;
15     @Override
16     protected void onCreate(Bundle savedInstanceState) {
17         super.onCreate(savedInstanceState);
18         setContentView(R.layout.activity_main);
19         btn_new  = (Button) findViewById(R.id.newfragment);
20         btn_back = (Button) findViewById(R.id.backfragment);
21         //新建一个新的fragment
22         btn_new.setOnClickListener(new OnClickListener() {
23             
24             @Override
25             public void onClick(View v) {
26                 // TODO Auto-generated method stub
27                 //创建管理者对象
28                 FragmentManager manager = getFragmentManager();
29                 //创建事务对象
30                 FragmentTransaction action = manager.beginTransaction();
31             
32                 action.replace(R.id.show_fragment, fragment);
33                 action.commit();
34                 
35             }
36         });
37         
38         //返回
39         btn_back.setOnClickListener(new OnClickListener() {
40             
41             @Override
42             public void onClick(View v) {
43                 // TODO Auto-generated method stub
44                 onBackPressed();
45             }
46         });
47     }
48     
49     
50 
51 }

1 //创建管理者对象
2                 FragmentManager manager = getFragmentManager();
3                 //创建事务对象
4                 FragmentTransaction action = manager.beginTransaction();            
5                 MyFragment fragment = new MyFragment();
6                 action.replace(R.id.show_fragment, fragment);
7                 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、

 1 package com.xqx_backfragment;
 2 
 3 import android.app.Activity;
 4 import android.app.FragmentManager;
 5 import android.app.FragmentTransaction;
 6 import android.os.Bundle;
 7 import android.view.View;
 8 import android.view.View.OnClickListener;
 9 import android.widget.Button;
10 
11 public class MainActivity extends Activity {
12     
13     private Button btn_new;
14     private Button btn_back;
15     @Override
16     protected void onCreate(Bundle savedInstanceState) {
17         super.onCreate(savedInstanceState);
18         setContentView(R.layout.activity_main);
19         btn_new  = (Button) findViewById(R.id.newfragment);
20         btn_back = (Button) findViewById(R.id.backfragment);
21         //新建一个新的fragment
22         btn_new.setOnClickListener(new OnClickListener() {
23             
24             @Override
25             public void onClick(View v) {
26                 // TODO Auto-generated method stub
27                 //创建管理者对象
28                 FragmentManager manager = getFragmentManager();
29                 //创建事务对象
30                 FragmentTransaction action = manager.beginTransaction();
31             
32                 MyFragment fragment = new MyFragment();
33                 action.add(R.id.show_fragment, fragment);
34                 action.addToBackStack(null);
35                 action.commit();
36                 
37             }
38         });
39         
40         //返回
41         btn_back.setOnClickListener(new OnClickListener() {
42             
43             @Override
44             public void onClick(View v) {
45                 // TODO Auto-generated method stub
46                 onBackPressed();
47             }
48         });
49     }
50     
51     
52 
53 }

1 //创建管理者对象
2                 FragmentManager manager = getFragmentManager();
3                 //创建事务对象
4                 FragmentTransaction action = manager.beginTransaction();
5             
6                 MyFragment fragment = new MyFragment();
7                 action.add(R.id.show_fragment, fragment);
8                 action.addToBackStack(null);
9                 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

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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

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

正确写法：

1 //创建管理者对象
2                 FragmentManager manager = getFragmentManager();
3                 //创建事务对象
4                 FragmentTransaction action = manager.beginTransaction();            
5                 MyFragment fragment = new MyFragment();
6                 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()

 1 //创建管理者对象
 2                 FragmentManager manager = getFragmentManager();
 3                 //创建事务对象
 4                 FragmentTransaction action = manager.beginTransaction();            
 5                 MyFragment fragment = new MyFragment();
 6                 action.add(R.id.show_fragment, fragment);
 7                 action.commit();
 8                 MyFragment fragment1 = new MyFragment();
 9                 action.add(R.id.show_fragment, fragment1);
10                 action.commit();

正确写法：

 1 //创建管理者对象
 2                 FragmentManager manager = getFragmentManager();
 3                 //创建事务对象
 4                 FragmentTransaction action = manager.beginTransaction();            
 5                 MyFragment fragment = new MyFragment();
 6                 action.add(R.id.show_fragment, fragment);
 7                 action.addToBackStack(null);
 8                 action.commit();
 9                 
10                 action = manager.beginTransaction();            
11                 MyFragment fragment1 = new MyFragment();
12                 action.add(R.id.show_fragment, fragment1);
13                 action.addToBackStack(null);
14                 action.commit();