Android-Fragment(2)-在Activity中动态添加删除

1. 前言

接着上一篇

2. 开发步骤

1. 取得FragmentTransaction实例

  FragmentManager manager=getFragmentManager();         
  FragmentTransaction           transaction=manager.beginTransaction();      

2. 调用add方法添加fragment到布局

transaction.add(R.id.main, first);

• 这里R.id.main是布局的地址，自己可以在activity_main.xml设置
  android:id="@+id/main"
• first是所创建的Fragment类的实例

   Fragment first;
   first =new FirstFragment();

3. 调用commit()方法

transaction.commit();
为了给Activity提交改变事物，必须调用commit方法

到这里就可以正常的添加fragment了。
注意：每个事务（提交给Activity的每个变化称为一个事务）都需要一个取得一次fragmenttransaction对象

当然，我们的每次变化都可以用transaction.addToBackStack(null);方法保存到Activity的back stack,这是一个栈，可以返回你之前存入其中的状态

当fragment移除时，fragment会被销毁，而在commit()提交之前使用addToBackStack，他只会停止，如果导航回来，fragment就会恢复。

3. 代码;

activity_main.xml

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/main"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="com.example.second.MainActivity" >
RelativeLayout>

firstfragment.xml

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="200dp"
    android:background="#FF0000" >
    <TextView
        android:layout_width="match_parent"
        android:layout_height="146dp"
        android:text="this is first fragment" />
FrameLayout>

secondfragment.xml

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
     android:layout_width="match_parent"
    android:layout_height="200dp"
    android:background="#FFFF11"
    android:layout_marginTop="300dp"
   >
    <TextView
        android:id="@+id/textView1"
        android:layout_width="match_parent"
        android:layout_height="100dp"
        android:text="this is second fragment" />  
FrameLayout>

FirstFragment.java

public class FirstFragment extends Fragment {
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        return inflater.inflate(R.layout.firstfrgment,container,false);
    }
}

SecondFragment.java

public class SecondFragment extends Fragment {
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        return inflater.inflate(R.layout.secondfragment,container,false);
    }
}

MainActivity.java

public class MainActivity extends ActionBarActivity {
    FirstFragment first;
    SecondFragment second;
    FragmentTransaction transaction;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
         first =new FirstFragment();
         second =new SecondFragment();             
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
         FragmentManager manager=getFragmentManager();          
            transaction=manager.beginTransaction();


        int id = item.getItemId();
        if (id == R.id.add_first) {
            transaction.add(R.id.main, first);  
            transaction.addToBackStack(null);


        }
        else if(id==R.id.add_second){
            transaction.add(R.id.main, second);
            transaction.addToBackStack(null);//Log下显示BackStack元素个数

        }
        else if(id==R.id.remove_first){
            //transaction.replace(R.id.main, first);
            transaction.remove(first);
            transaction.addToBackStack(null);


        }
        else if(id==R.id.remove_second){
            transaction.remove(second);
            transaction.addToBackStack(null);

        }
        transaction.commit();
         int TAG = getFragmentManager().getBackStackEntryCount();
        Log.d("TAG",String.valueOf(TAG));
        if(TAG>0)
            Log.d("TAG",getFragmentManager().getBackStackEntryAt(TAG-1).toString());
        return true;
    }
}

效果图: