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" android:drawableTop="@drawable/bottom_1" /> <RadioButton android:id="@+id/radio_button1" android:drawableTop="@drawable/bottom_2" /> <RadioButton android:id="@+id/radio_button2" android:drawableTop="@drawable/bottom_3" /> <RadioButton android:id="@+id/radio_button3" android:drawableTop="@drawable/bottom_4" /> <RadioButton android:id="@+id/radio_button4" 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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