TabLayout+ViewPager+Fragment模式在应用中必不可少，有时候我们可能会遇到tab栏会动态改变的问题，如新增，或删减，这时候就需要把viewpager内相应的fragment新增或删减;
如想做以下等操作？
1、更新单个item
mDataList.remove(0);
mPagerAdapter.notifyDataSetChanged();
1、删掉viewpager内的所有view
viewpage.removeAllViews();
2、在adapter中重现以下方法
@Override
public int getItemPosition(Object object) {
// 最简单解决 notifyDataSetChanged() 页面不刷新问题的方法
return POSITION_NONE;
}
@Override
public void destroyItem(ViewGroup container, int position, Object object) {
// 把 Object 强转为 View，然后将 view 从 ViewGroup 中清除
container.removeView((View) object);
}
...................
你会发现都会无效，
具体原因如下：
罪魁祸首是FragmentPagerAdapter，相关文章介绍，这个adapter会默认把我们的所有加载的view放到缓存中，每次会先从缓存中加载，提升效率，这就难怪了，怎么删都删不掉。
最终发现了 我们还有另外一个PagerAdapter可以使用，那就是FragmentStatePagerAdapter也是最终的解决方法，该 PagerAdapter 的实现将只保留当前页面，当页面离开视线后，就会被消除，释放其资源。
一下是两种场景的使用方法
1、继承v4包的fragment使用
直接继承FragmentStatePagerAdapter即可跟FragmentPagerAdapter一样使用，但还是需要重写一下方法
@Override
public int getItemPosition(Object object) {
// 最简单解决 notifyDataSetChanged() 页面不刷新问题的方法
return POSITION_NONE;
}
@Override
public void destroyItem(ViewGroup container, int position, Object object) {
// 把 Object 强转为 View，然后将 view 从 ViewGroup 中清除
container.removeView((View) object);
}
2、继承app包的fragment的使用，
由于相关的adapter默认的都是继承v4包的，但当我们的fragment是继承app包的时候就会出现问题，解决方法就是把继承v4包的FragmentStatePagerAdapter源码拷贝出来把里面的继承v4包的类全部改为继承app包，当然最终的父类PagerAdapter是不能修改的还是继承的v4包，这个可以不用管。同时在你的子类中同样需要重写以下方法
@Override
public int getItemPosition(Object object) {
// 最简单解决 notifyDataSetChanged() 页面不刷新问题的方法
return POSITION_NONE;
}
@Override
public void destroyItem(ViewGroup container, int position, Object object) {
// 把 Object 强转为 View，然后将 view 从 ViewGroup 中清除
container.removeView((View) object);
}
以下是继承app包的FragmentStatePagerAdapter类，可直接使用：
package cn.longmaster.hospital.doctor.ui.college.adapter;
import android.app.Fragment;
import android.app.FragmentManager;
import android.app.FragmentTransaction;
import android.os.Bundle;
import android.os.Parcelable;
import android.support.v4.view.PagerAdapter;
import android.util.Log;
import android.view.View;
import android.view.ViewGroup;
import java.util.ArrayList;
/**
* Created by W·H·K on 2018/9/17.
*/
public abstract class MyFragmentStatePagerAdapter extends PagerAdapter {
private static final String TAG = "FragmentStatePagerAdapter";
private static final boolean DEBUG = false;
private final FragmentManager mFragmentManager;
private FragmentTransaction mCurTransaction = null;
private ArrayList<Fragment.SavedState> mSavedState = new ArrayList<Fragment.SavedState>();
private ArrayList<Fragment> mFragments = new ArrayList<Fragment>();
private Fragment mCurrentPrimaryItem = null;
public MyFragmentStatePagerAdapter(FragmentManager fm) {
mFragmentManager = fm;
}
/**
* Return the Fragment associated with a specified position.
*/
public abstract Fragment getItem(int position);
@Override
public void startUpdate(ViewGroup container) {
}
@Override
public Object instantiateItem(ViewGroup container, int position) {
// If we already have this item instantiated, there is nothing
// to do. This can happen when we are restoring the entire pager
// from its saved state, where the fragment manager has already
// taken care of restoring the fragments we previously had instantiated.
if (mFragments.size() > position) {
Fragment f = mFragments.get(position);
if (f != null) {
return f;
}
}
if (mCurTransaction == null) {
mCurTransaction = mFragmentManager.beginTransaction();
}
Fragment fragment = getItem(position);
if (mSavedState.size() > position) {
Fragment.SavedState fss = mSavedState.get(position);
if (fss != null) {
fragment.setInitialSavedState(fss);
}
}
while (mFragments.size() <= position) {
mFragments.add(null);
}
fragment.setMenuVisibility(false);
fragment.setUserVisibleHint(false);
mFragments.set(position, fragment);
mCurTransaction.add(container.getId(), fragment);
return fragment;
}
@Override
public void destroyItem(ViewGroup container, int position, Object object) {
Fragment fragment = (Fragment) object;
if (mCurTransaction == null) {
mCurTransaction = mFragmentManager.beginTransaction();
}
while (mSavedState.size() <= position) {
mSavedState.add(null);
}
mSavedState.set(position, mFragmentManager.saveFragmentInstanceState(fragment));
mFragments.set(position, null);
mCurTransaction.remove(fragment);
}
@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();
}
}
@Override
public boolean isViewFromObject(View view, Object object) {
return ((Fragment) object).getView() == view;
}
@Override
public Parcelable saveState() {
Bundle state = null;
if (mSavedState.size() > 0) {
state = new Bundle();
Fragment.SavedState[] fss = new Fragment.SavedState[mSavedState.size()];
mSavedState.toArray(fss);
state.putParcelableArray("states", fss);
}
for (int i = 0; i < mFragments.size(); i++) {
Fragment f = mFragments.get(i);
if (f != null && f.isAdded()) {
if (state == null) {
state = new Bundle();
}
String key = "f" + i;
mFragmentManager.putFragment(state, key, f);
}
}
return state;
}
@Override
public void restoreState(Parcelable state, ClassLoader loader) {
if (state != null) {
Bundle bundle = (Bundle) state;
bundle.setClassLoader(loader);
Parcelable[] fss = bundle.getParcelableArray("states");
mSavedState.clear();
mFragments.clear();
if (fss != null) {
for (int i = 0; i < fss.length; i++) {
mSavedState.add((Fragment.SavedState) fss[i]);
}
}
Iterable<String> keys = bundle.keySet();
for (String key : keys) {
if (key.startsWith("f")) {
int index = Integer.parseInt(key.substring(1));
Fragment f = mFragmentManager.getFragment(bundle, key);
if (f != null) {
while (mFragments.size() <= index) {
mFragments.add(null);
}
f.setMenuVisibility(false);
mFragments.set(index, f);
} else {
Log.w(TAG, "Bad fragment at key " + key);
}
}
}
}
}
}