先來講一下寫這篇文章的原因：就是Fragment懶加載網(wǎng)上的代碼弄過來以后配合ViewPager的FragmentPagerAdapter都沒問題统屈，但是畢竟使用FragmentPagerAdapter每個(gè)fragment都會(huì)保持在內(nèi)存中商乎。而且自己項(xiàng)目中有幾十個(gè)Fragment所以部分機(jī)型就OOM了
接下來附上網(wǎng)上的fragment懶加載代碼 在代碼中我會(huì)注釋我改了哪里娶桦。
package com.global.motortravel.ui.base;
import android.annotation.TargetApi;
import android.app.Activity;
import android.content.Context;
import android.content.Intent;
import android.os.Build;
import android.os.Bundle;
import android.support.annotation.Nullable;
import android.support.v4.app.Fragment;
import android.util.DisplayMetrics;
import android.util.Log;
import android.view.View;
import com.global.motortravel.R;
public abstract class BaseFragment extends Fragment {
/**
* 是否已被加載過一次，第二次就不再去請(qǐng)求數(shù)據(jù)了
*/
protected boolean mHasLoadedOnce;
/**
* rootView是否初始化標(biāo)志，防止回調(diào)函數(shù)在rootView為空的時(shí)候觸發(fā)
*/
private boolean hasCreateView;
/**
* 當(dāng)前Fragment是否處于可見狀態(tài)標(biāo)志，防止因ViewPager的緩存機(jī)制而導(dǎo)致回調(diào)函數(shù)的觸發(fā)
*/
private boolean isFragmentVisible;
//使用屬性保存當(dāng)前狀態(tài)FragmentStatePagerAdapter 跨好幾個(gè)頁面切換時(shí)getUserVisibleHint()在 onViewCreated中獲取到的值不準(zhǔn)確
private boolean isVisibleToUser=false;
protected boolean mHasLoadData=false;//在頁面被銷毀后是否保持了之前加載的數(shù)據(jù)穴店，此字段決定是否重新加載數(shù)據(jù)這樣就可以達(dá)到FragmentPagerAdapter的效果
/**
* onCreateView()里返回的view，修飾為protected,所以子類繼承該類時(shí)拿穴，在onCreateView里必須對(duì)該變量進(jìn)行初始化
*/
protected View rootView;
protected int mScreenWidth;
protected int mScreenHeight;
public Context context;
public Activity activity;
@TargetApi(23)
@Override
public void onAttach(Context context) {
super.onAttach(context);
onAttachToContext(context);
}
/*
* Deprecated on API 23
* Use onAttachToContext instead
*/
@SuppressWarnings("deprecation")
@Override
public void onAttach(Activity activity) {
super.onAttach(activity);
if (Build.VERSION.SDK_INT < Build.VERSION_CODES.M) {
onAttachToContext(activity);
}
if (this.activity == null) {
this.activity = activity;
}
}
protected void onAttachToContext(Context context) {
this.context = context;
}
@Override
public void onCreate(@Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
DisplayMetrics dm = getResources().getDisplayMetrics();
mScreenWidth = dm.widthPixels;
mScreenHeight = dm.heightPixels;
if (this.activity == null) {
this.activity = getActivity();
}
initPresenter();
}
protected void initEvents() {
}
protected void initViews() {
}
protected void initPresenter() {
}
@Override
public void onViewCreated(View view, @Nullable Bundle savedInstanceState) {
super.onViewCreated(view, savedInstanceState);
if (!hasCreateView && isVisibleToUser) {//網(wǎng)上這里是getUserVisibleHint()這里跨多個(gè)fragment切換時(shí)取到的值不對(duì)所以直接使用剛才在setUserVisibleHint賦值的屬性
onFragmentVisibleChange(true);
isFragmentVisible = true;
}
}
/**************************************************************
* 自定義的回調(diào)方法泣洞，子類可根據(jù)需求重寫
*************************************************************/
/**
* 當(dāng)前fragment可見狀態(tài)發(fā)生變化時(shí)會(huì)回調(diào)該方法
* 如果當(dāng)前fragment是第一次加載，等待onCreateView后才會(huì)回調(diào)該方法默色，其它情況回調(diào)時(shí)機(jī)跟 {@link #setUserVisibleHint(boolean)}一致
* 在該回調(diào)方法中你可以做一些加載數(shù)據(jù)操作球凰，甚至是控件的操作，因?yàn)榕浜蟜ragment的view復(fù)用機(jī)制腿宰，你不用擔(dān)心在對(duì)控件操作中會(huì)報(bào) null 異常
*
* @param isVisible true 不可見 -> 可見
* false 可見 -> 不可見
*/
protected void onFragmentVisibleChange(boolean isVisible) {
}
@Override
public void setUserVisibleHint(boolean isVisibleToUser) {
super.setUserVisibleHint(isVisibleToUser);
this.isVisibleToUser=isVisibleToUser;//跨好幾個(gè)fragment切換此次的isVisibleToUser正常的所以在這里賦值
if (rootView == null) {
return;
}
hasCreateView = true;
if (isVisibleToUser) {
onFragmentVisibleChange(true);
isFragmentVisible = true;
return;
}
if (isFragmentVisible) {
onFragmentVisibleChange(false);
isFragmentVisible = false;
}
}
}
接下來將下我們繼承Basefragment的fragment
@Override
protected void onFragmentVisibleChange(boolean isVisible) {
//不可見 或不是第一次加載數(shù)據(jù)就返回
if (!isVisible || mHasLoadedOnce) {
return;
}
//頁面是否被銷毀過 沒有銷毀過就去加載數(shù)據(jù)
if (!mHasLoadData) {
binding.swipeLayout.setRefreshing(true);
binding.swipeLayout.postDelayed(new Runnable() {
@Override
public void run() {
presenter.getHotTravelList(page, pageSize);
}
}, 800);
}
mHasLoadedOnce = true;
}
然后就是頁面銷毀數(shù)據(jù)保存和頁面重新創(chuàng)建直接拿原先的數(shù)據(jù)
@Nullable
@Override
public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
//savedInstanceState 不為空說明頁面銷毀過呕诉，把銷毀前的數(shù)據(jù)取回來，這樣不要再次加載
if (savedInstanceState != null) {
travelInfoList = savedInstanceState.getParcelableArrayList(Constants.TRAVEL_INFO_LIST);
if (travelInfoList != null && travelInfoList.size() > 0)
//這里表示數(shù)據(jù)已經(jīng)加載無需去請(qǐng)求
mHasLoadData = true;
}
if (rootView == null) {
binding = DataBindingUtil.inflate(inflater, R.layout.fm_hot_travel, container, false);
rootView = binding.getRoot();
initViews();
}
return rootView;
}
@Override
public void onSaveInstanceState(Bundle outState) {
if (adapter.getTravelInfoList() != null) {
//保存當(dāng)前fragment的數(shù)據(jù)
outState.putParcelableArrayList(Constants.TRAVEL_INFO_LIST, (ArrayList<? extends Parcelable>) adapter.getTravelInfoList());
}
super.onSaveInstanceState(outState);
}
大致這么多吃度，同事都是吃飯了我也跟上甩挫。上面效果達(dá)到 fragment 頁面 加載數(shù)據(jù) 緩存setOffscreenPageLimit(1);你所設(shè)置頁面 過后銷毀 重新創(chuàng)建拉回之前數(shù)據(jù)也不需要加載，內(nèi)存還不會(huì)隨fragment過多而OOM椿每。
