Android TabLayout+ViewPager+Fragment實現tab欄的時候，無法實時更新ViewPager內的Fragment問題終極解決方法
TabLayout+ViewPager+Fragment模式在應用中必不可少，有時候我們可能會遇到tab欄會動態改變的問題，如新增，或刪減，這時候就需要把viewpager內相應的fragment新增或刪減;
如想做以下等操作？
1、更新單個item
mDataList.remove(0);
mPagerAdapter.notifyDataSetChanged();
1、刪掉viewpager內的所有view
viewpage.removeAllViews();
2、在adapter中重現以下方法
@Override
public int getItemPosition(Object object) {
// 最簡單解決 notifyDataSetChanged() 頁面不重新整理問題的方法
return POSITION_NONE;
}
@Override
public void destroyItem(ViewGroup container, int position, Object object) {
// 把 Object 強轉為 View，然後將 view 從 ViewGroup 中清除
container.removeView((View) object);
}
...................
你會發現都會無效，
具體原因如下：
罪魁禍首是
最終發現了 我們還有另外一個PagerAdapter可以使用，那就是FragmentStatePagerAdapter也是最終的解決方法，該 PagerAdapter 的實現將只保留當前頁面，當頁面離開視線後，就會被消除，釋放其資源。
一下是兩種場景的使用方法
1、繼承v4包的fragment使用
直接繼承FragmentStatePagerAdapter即可跟FragmentPagerAdapter
@Override
public int getItemPosition(Object object) {
// 最簡單解決 notifyDataSetChanged() 頁面不重新整理問題的方法
return POSITION_NONE;
}
@Override
public void destroyItem(ViewGroup container, int position, Object object) {
// 把 Object 強轉為 View，然後將 view 從 ViewGroup 中清除
container.removeView((View) object);
}
2、繼承app包的fragment的使用，
由於相關的adapter預設的都是繼承v4包的，但當我們的fragment是繼承app包的時候就會出現問題，解決方法就是把繼承v4包的FragmentStatePagerAdapter原始碼拷貝出來把裡面的繼承v4包的類全部改為繼承app包，當然最終的父類PagerAdapter是不能修改的還是繼承的v4包，這個可以不用管。同時在你的子類中同樣需要重寫以下方法
@Override
public int getItemPosition(Object object) {
// 最簡單解決 notifyDataSetChanged() 頁面不重新整理問題的方法
return POSITION_NONE;
}
@Override
public void destroyItem(ViewGroup container, int position, Object object) {
// 把 Object 強轉為 View，然後將 view 從 ViewGroup 中清除
container.removeView((View) object);
}
以下是繼承app包的FragmentStatePagerAdapter類，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);
}
}
}
}
}
}