Android 保存Fragment 切换状态实例代码

2019-12-12 05:55:07

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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。

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