FragmentPagerAdapter 頁面類型、數量、內容更新問題
場景
存在一種需求，當用戶系統中，屬於某一組織的用戶登陸以後（或者帳戶切換），要求主頁面顯示不一樣的ViewPager + Fragment組合，而且要求app無需退出就能刷新組合以及組合中的頁面。android
此外，爲了保證Fragment和Fragment中View沒必要要的inflate和渲染，要求儘量重用已存在的Fragment和View。顯然FragmentPagerAdapter是首選。可是存在三個問題：緩存
一、FragmentPagerAdapter默認沒法更新，須要重寫getItemPosition，返回值爲PagerAdapter.POSITION_NONE才能夠更新app
二、重用的Fragment設置參數沒法從新初始化ide
三、重用的Fragment類型和新的Fragment類型存在不匹配問題，如舊的UserFragment頁面，可是新的要求是ListFragment，因此類型存在問題。oop
解決方案
咱們須要重寫FragmentPagerAdapter，但問題是存在各類不方便的因素，所以，咱們須要自定義FragmentPagerAdapter。post
public abstract class CustomFragmentPagerAdapter extends PagerAdapter {
private static final String TAG = "FragmentPagerAdapter";
private static final boolean DEBUG = false;
private final FragmentManager mFragmentManager;
private FragmentTransaction mCurTransaction = null;
private Fragment mCurrentPrimaryItem = null;
private final LongSparseArray<String> fragmentViewTypeManager = new LongSparseArray<String>();
public CustomFragmentPagerAdapter(FragmentManager fm) {
mFragmentManager = fm;
}
@Override
public void startUpdate(ViewGroup container) {
if (container.getId() == View.NO_ID) { //viewPager必須賦值ID，不然沒法添加fragment
throw new IllegalStateException("ViewPager with adapter " + this
+ " requires a view id");
}
}
@SuppressWarnings("ReferenceEquality")
@Override
public Object instantiateItem(ViewGroup container, int position) {
mCurTransaction = beginTransaction();
final long itemId = getItemId(position);
final int count = this.getFragmentTypeCount();
int fragmentType = 0;
if(count>0){
fragmentType = getItemFragmentType(position);
}
if(fragmentType>0 && fragmentType>=count){
throw new IllegalArgumentException("{fragmentType's number >= fragmentTypeCount's number} is illegal");
}
// 生成tag，用於保存和標記每一個位置的fragment
final String name = makeFragmentName(container.getId(), itemId); //生成tag
final String oldFragmentName = fragmentViewTypeManager.get(fragmentType);
Fragment fragment = mFragmentManager.findFragmentByTag(name);
if (fragment != null) {
final String fragmentClassName = fragment.getClass().getName();
if(!fragmentClassName.equals(oldFragmentName)) {
//若是發現新舊類型不一致，移除舊類型
if (DEBUG) Log.v(TAG, "Removeing item #" + itemId + ": f=" + fragment);
mCurTransaction.remove(fragment);
//獲取新類型
fragment = getItem(null,position);
if (DEBUG) Log.v(TAG, "Adding item #" + itemId + ": f=" + fragment);
mCurTransaction.add(container.getId(), fragment,name);
}else {
Fragment newFragment = getItem(fragment,position);
//獲取newFragment ，若是2次fragment不一致，移除舊的fragment
if(newFragment!=fragment){
if (DEBUG) Log.v(TAG, "Removeing item #" + itemId + ": f=" + fragment);
mCurTransaction.remove(fragment);
fragment = newFragment;
if (DEBUG) Log.v(TAG, "Adding item #" + itemId + ": f=" + fragment);
mCurTransaction.add(container.getId(), fragment,name);
}else {
//若是獲取到fragment與原來的是同一個，attach便可
if (DEBUG) Log.v(TAG, "Attaching item #" + itemId + ": f=" + fragment);
mCurTransaction.attach(fragment);
}
}
} else {
fragment = getItem(fragment,position);
if (DEBUG) Log.v(TAG, "Adding item #" + itemId + ": f=" + fragment);
mCurTransaction.add(container.getId(), fragment,name);
}
if(fragment!=null){
//保存類型，用來校驗緩存的正確性
fragmentViewTypeManager.put(fragmentType,fragment.getClass().getName());
}
if (fragment != mCurrentPrimaryItem) {
fragment.setMenuVisibility(false);
fragment.setUserVisibleHint(false);
}
return fragment;
}
@Override
public void destroyItem(ViewGroup container, int position, Object object) {
mCurTransaction = beginTransaction();
if (DEBUG) Log.v(TAG, "Detaching item #" + getItemId(position) + ": f=" + object
+ " v=" + ((Fragment)object).getView());
mCurTransaction.detach((Fragment)object); //dattach fragment
}
@SuppressWarnings("ReferenceEquality")
@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; //設置當前的fragment
}
}
@Override
public void finishUpdate(ViewGroup container) {
if (mCurTransaction != null) {
mCurTransaction.commitNowAllowingStateLoss();
//提交，注意該方法將任務加入到mainLooper中，可能產生延遲
mCurTransaction = null;
}
}
@Override
public boolean isViewFromObject(View view, Object object) {
return ((Fragment)object).getView() == view;
}
@Override
public Parcelable saveState() {
return null;
}
@Override
public void restoreState(Parcelable state, ClassLoader loader) {
}
/**
*
* 獲取每一個fragment的id，注意保證惟一性
*/
public long getItemId(int position) {
return position;
}
//生成tag
public static String makeFragmentName(int viewId, long id) {
return "android:switcher:" + viewId + ":" + id;
}
public FragmentTransaction beginTransaction(){
if (mCurTransaction == null) {
mCurTransaction = mFragmentManager.beginTransaction();
}
return mCurTransaction;
}
public FragmentManager getFragmentManager(){
return mFragmentManager;
}
/**
* 獲取當前位置的fragment
*/
public abstract Fragment getItem(Fragment contentFragment,int position);
/**
* 獲取當前位置的type FragmentType
*/
public abstract int getItemFragmentType(int position);
/**
* 獲取當前類型的數量 FragmentCount
*/
public abstract int getFragmentTypeCount();
/**
* 在ViewPager中調用，告訴ViewPager該位置的Fragment是能夠被替換和更新的
* 這裏人能夠繼續優化，因爲ViewPager.LayoutParams中的position是非public的，所以要優化能夠在該類的基類中完成
*/
@Override
public int getItemPosition(Object object) {
if(!(object instanceOf Fragment))
{
return PagerAdapter.POSITION_NONE;
}
return PagerAdapter.POSITION_UNCHANGED;
}
public boolean isEmpty(){
return getCount()==0;
}
}
到這裏，咱們即可以實現他的子類優化
static class MyPagerAdapter extends CustomFragmentPagerAdapter{
private ArrayList<FragmentTabEntity> dataEntities;
private final String TAG_NAME = "MyPagerAdapter ";
public MyPagerAdapter(FragmentManager fm,List<FragmentTabEntity> dataEntities) {
super(fm);
this.dataEntities = new ArrayList<>();
this.dataEntities.addAll(dataEntities);
}
@SuppressWarnings("unchecked")
public void updateDataEntities(List<FragmentTabEntity> dataEntities) {
this.dataEntities.clear();
if(dataEntities!=null && dataEntities.size()>0){
this.dataEntities.addAll(dataEntities);
}
this.notifyDataSetChanged();
}
@Override
public CharSequence getPageTitle(int position) {
final FragmentTabEntity entity = dataEntities.get(position);
return entity.getTitle();
}
@Override
public int getItemFragmentType(int position) {
final FragmentTabEntity dataEntity = dataEntities.get(position);
return dataEntity.getType(position); //獲取類型，注意，最大值不能大於getFragmentTypeCount()
}
@Override
public int getFragmentTypeCount() {
return FragmentTabEntity.getTotalTypeCount();
//獲取全部fragment的類型數量，通常是固定值，主要看程序實現方式了
}
@Override
public Fragment getItem(Fragment contentFragment,int position) {
final int fragmentType = getItemFragmentType(position);
final FragmentTabEntity dataEntity = dataEntities.get(position);
BaseFragment fragment = null;
if(contentFragment==null) {
if (fragmentType == 0) {
fragment = new IndexFragment();
} else if(fragmentType ==1){
fragment = new UserFragment();
} else if(fragmentType ==2){
fragment = new WebFragment();
}else if(fragmentType ==3){
fragment = new ListFragment();
}
}else{
fragment = (BaseFragment) contentFragment;
}
fragment.setPosition(position);
if(fragment!=null) {
Bundle fb = new Bundle();
fb.putString(BaseFragment.KEY_TYPE, dataEntity.getType());
fb.putString(BaseFragment.KEY_TITLE, dataEntity.getTitle());
fragment.setNoneStateArguments(fb); //使用非狀態參數傳遞方法
}
return fragment;
}
@Override
public int getCount() {
return dataEntities.size();
}
}
使用方法ui
private MyPagerAdapter mTabPagerAdapter;
public void updatePager(List<FragmentTabEntity> data)
{
if((pager.getAdapter() instanceof MyPagerAdapter)){
mTabPagerAdapter = (MyPagerAdapter) pager.getAdapter();
}
if(mTabPagerAdapter==null){
mTabPagerAdapter = new MyPagerAdapter(getChildFragmentManager(),data);
pager.setAdapter(mTabPagerAdapter);
}else{
mTabPagerAdapter.updateDataEntities(data);
}
}
Fragment ViewCache問題 & 生命週期問題
到這一步事實上咱們的自定義FragmentPagerAdapter已經完成了，可是這裏還存在不完美的問題，那就是Fragment中添加了View Cache的狀況，此外，對於生命週期的控制，可能或多或少出現舊頁面向新頁面過渡時閃爍問題。this
一、View Cache 問題spa
先來看看這種Fragment的定義方式
public class BaseFragment extends Fragment{
private SoftReference<View> mRootViewCache = null; //實現viewcache
private boolean isFinishedInflated = false;
private Bundle mNoneStateArguments;
private int position = -1;
public void setPosition(int position){
this.position = position;
}
public int getPosition(){
return this.position;
}
@Nullable
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState){
View root = null;
if(!cacheIsEmpty()){
root = mRootViewCache.get();
}
if(root==null){
root = inflater.inflate(R.layout.base_view_layout, container, false);
root.findViewById(R.id.toolbar).setVisibility(View.GONE);
mRootViewCache = new SoftReference<View>(root);
}
return root;
}
@Override
public void onViewCreated(View view, @Nullable Bundle savedInstanceState) {
super.onViewCreated(view, savedInstanceState);
try {
isFinishedInflated = true;
renderFragmentView(view);
} catch (Exception e) {
e.printStackTrace();
}
}
private boolean cacheIsEmpty(){
return mRootViewCache==null || mRootViewCache.get()==null;
}
@Override
public void onResume() {
super.onResume();
if(getUserVisibleHint() ){
onFragmetShow();
}
}
@Override
public void setUserVisibleHint(boolean isVisibleToUser) {
super.setUserVisibleHint(isVisibleToUser);
if(!isFinishedInflated) return;
if( getUserVisibleHint()){
onFragmetShow();
}else if(isResumed()){
onFragmetHide();
}
}
@Override
public void onStop() {
super.onStop();
if(getUserVisibleHint()){
onFragmetHide();
}
}
public void onFragmetShow(){
if(getView()==null) return ;
getView().post(new Runnable(){
public void run(){
//這裏能夠用來獲取Fragment的參數，而後更新
}
});
}
public void onFragmetHide(){
}
public void setNoneStateArguments(Bundle bundle){ //解決已初始化狀態的參數刷新問題
this.mNoneStateArguments = bundle;
}
public void getNoneStateArguments(){
return this.mNoneStateArguments!=null? this.mNoneStateArguments:new Bundle();
}
}
對於原生頁面，新舊頁面閃爍並非很明顯，可是對於Webview頁面，這種閃爍很明顯，致使該問題的緣由是View Cache，所以，咱們須要在Fragment中添加clearView方法來清空一下Cache
public void clearView() {
if(mRootViewCache!=null){
mRootViewCache.clear();
}
}
在MyPagerAdapter的getItem方法中，咱們有必要植入一個flag
@Override
public Fragment getItem(Fragment contentFragment,int position) {
final int fragmentType = getItemFragmentType(position);
final FragmentTabEntity dataEntity = dataEntities.get(position);
BaseFragment fragment = null;
if(contentFragment==null) {
if (viewType == 0) {
fragment = new IndexFragment();
} else if(fragmentType ==1){
fragment = new UserFragment();
} else if(fragmentType ==2){
fragment = new WebFragment();
}else if(fragmentType ==3){
fragment = new ListFragment();
}
}else{
fragment = (BaseFragment) contentFragment;
}
final Bundle fa = fragment.getArguments();
if(fa!=null) {
final String oldTag = fa.getString("md5", "");
if (!TextUtils.isEmpty(oldTag) && !oldUrl.oldTag(dataEntity.getMd5())) {
fragment.clearView(); //若是tag不一致，清空一下view cache
}
}
if(fragment!=null) {
Bundle fb = new Bundle();
fb.putString("md5",dataEntity.getMd5()); //植入新的md5 tag
fb.putString(BaseFragment.KEY_TYPE, dataEntity.getType());
fb.putString(BaseFragment.KEY_TITLE, dataEntity.getTitle());
fragment.setArguments(fb);
}
return fragment;
}
二、生命週期問題
關於onFragmentShow與onFragmentHide的生命週期用法，請參考《Fragment頁面切換》，這裏咱們主要說一下mainLooper問題
public void onFragmetShow(){
if(getView()==null) return ;
getView().post(new Runnable(){
public void run(){
//這裏能夠用來獲取Fragment的參數，而後更新
}
});
}
若是要更新UI，咱們建議這裏使用post將消息發送到mainLooper，爲何要這樣呢？
主要緣由是FragmentPagerAdapter的finishUpdate中使用了commit方法，這個方法是將任務發送到mainLooper的隊列中，而不是當即執行。
@Override
public void finishUpdate(ViewGroup container) {
if (mCurTransaction != null) {
mCurTransaction.commitNowAllowingStateLoss();
mCurTransaction = null;
}
}
基於隊列的先進先出，FragmentTransaction將更新消息加入到Fragment add/attach消息以後，咱們若是直接獲取argument可能出現數據不一致的問題，所以咱們須要將咱們的方法做爲任務一樣放入到mainLooper中。若是不這麼作，可能致使獲取到的argument是舊的，致使咱們更新時使用了舊的參數。固然，能夠參考《Android Fragment重複添加問題解決方法》，原理基本相同。
以上是通常常見的問題，至於其餘問題，能夠留言。
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