前言

 一般频繁切换Fragment会导致频繁的释放和创建，如果Fragment比较臃肿体验就非常不好了，这里分享一个方法。

 正文

 一、应用场景

  1、不使用ViewPager

  2、不能用replace来切换Fragment，会导致Fragment释放（调用onDestroyView）

 二、实现

1、xml

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

 <FrameLayout
  android:id="@+id/container"
  android:layout_width="match_parent"
  android:layout_height="0dip"
  android:layout_weight="1.0" >
 </FrameLayout>

 <RadioGroup
  android:id="@+id/main_radio"
  android:layout_width="fill_parent"
  android:layout_height="wrap_content"
  android:layout_gravity="bottom"
  android:gravity="bottom"
  android:layout_marginBottom="-6dp"
  android:orientation="horizontal" >

  <RadioButton
   android:id="@+id/radio_button0"
   style="@style/main_tab_bottom"
   android:drawableTop="@drawable/bottom_1" />

  <RadioButton
   android:id="@+id/radio_button1"
   style="@style/main_tab_bottom"
   android:drawableTop="@drawable/bottom_2" />

  <RadioButton
   android:id="@+id/radio_button2"
   style="@style/main_tab_bottom"
   android:drawableTop="@drawable/bottom_3" />

  <RadioButton
   android:id="@+id/radio_button3"
   style="@style/main_tab_bottom"
   android:drawableTop="@drawable/bottom_4" />

  <RadioButton
   android:id="@+id/radio_button4"
   style="@style/main_tab_bottom"
   android:drawableTop="@drawable/bottom_5" />
 </RadioGroup>

</LinearLayout>

代码说明：

    非常常见的底部放5个RadioButton，点击切换不同的Fragment。

  2、Activity

   为RadioButton设置setOnCheckedChangeListener事件，其他代码:

 public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
  if (isChecked) {
   Fragment fragment = (Fragment) mFragmentPagerAdapter.instantiateItem(mContainer, buttonView.getId());
   mFragmentPagerAdapter.setPrimaryItem(mContainer, 0, fragment);
   mFragmentPagerAdapter.finishUpdate(mContainer);
  } 
 }

 private FragmentPagerAdapter mFragmentPagerAdapter = new FragmentPagerAdapter(getSupportFragmentManager()) {

  @Override
  public Fragment getItem(int position) {
   switch (position) {
   case R.id.radio_button1:
    return new Fragment1();
   case R.id.radio_button2:
    return new Fragment2();
   case R.id.radio_button3:
    return new Fragment3();
   case R.id.radio_button4:
    return new Fragment4();
   case R.id.radio_button0:
   default:
    return new Fragment0();
   }
  }

  @Override
  public int getCount() {
   return 5;
  }
 };

代码说明：

   instantiateItem从FragmentManager中查找Fragment，找不到就getItem新建一个，setPrimaryItem设置隐藏和显示，最后finishUpdate提交事务， mContainer就是xml中的FrameLayout。

 三、FragmentPagerAdapter核心代码

 @Override
 public Object instantiateItem(ViewGroup container, int position) {
  if (mCurTransaction == null) {
   mCurTransaction = mFragmentManager.beginTransaction();
  }

  final long itemId = getItemId(position);

  // Do we already have this fragment?
  String name = makeFragmentName(container.getId(), itemId);
  Fragment fragment = mFragmentManager.findFragmentByTag(name);
  if (fragment != null) {
   if (DEBUG) Log.v(TAG, "Attaching item #" + itemId + ": f=" + fragment);
   mCurTransaction.attach(fragment);
  } else {
   fragment = getItem(position);
   if (DEBUG) Log.v(TAG, "Adding item #" + itemId + ": f=" + fragment);
   mCurTransaction.add(container.getId(), fragment,
     makeFragmentName(container.getId(), itemId));
  }
  if (fragment != mCurrentPrimaryItem) {
   fragment.setMenuVisibility(false);
   fragment.setUserVisibleHint(false);
  }

  return fragment;
 }

 @Override
 public void destroyItem(ViewGroup container, int position, Object object) {
  if (mCurTransaction == null) {
   mCurTransaction = mFragmentManager.beginTransaction();
  }
  if (DEBUG) Log.v(TAG, "Detaching item #" + getItemId(position) + ": f=" + object
    + " v=" + ((Fragment)object).getView());
  mCurTransaction.detach((Fragment)object);
 }

 @Override
 public void setPrimaryItem(ViewGroup container, int position, Object object) {
  Fragment fragment = (Fragment)object;
  if (fragment != mCurrentPrimaryItem) {
   if (mCurrentPrimaryItem != null) {
    mCurrentPrimaryItem.setMenuVisibility(false);
    mCurrentPrimaryItem.setUserVisibleHint(false);
   }
   if (fragment != null) {
    fragment.setMenuVisibility(true);
    fragment.setUserVisibleHint(true);
   }
   mCurrentPrimaryItem = fragment;
  }
 }

 @Override
 public void finishUpdate(ViewGroup container) {
  if (mCurTransaction != null) {
   mCurTransaction.commitAllowingStateLoss();
   mCurTransaction = null;
   mFragmentManager.executePendingTransactions();
  
} 
 public void setMenuVisibility(boolean menuVisible) {
        super.setMenuVisibility(menuVisible);
        if (this.getView() != null)
            this.getView().setVisibility(menuVisible ? View.VISIBLE : View.GONE);
    }
 }

FragmentPagerAdapter是support包自带的类。

四、注意

  之前自己模拟ViewPager用attach、setMenuVisibility、setUserVisibleHint来控制Fragment的显示隐藏，经常会出现Fragment重叠现象，非常头疼，换了这个之后目前没有发现重叠现象。

 结束：以上就是对Android Fragment 实例说明，希望能帮助有需要的同学。