android viewpager使用Fragment懒加载，滑到当前fragment才进行数据加载

前言：如果不做fragment的懒加载则每次进入activity就会初始化没必要的数据，消耗内存和网络流量，再每次自动销毁后也需要重新初始化fragment的数据，为此优化，我们要做fragment的懒加载，网络上关于懒加载的文章数不胜数，可是详细、全面，又有实际源码和例子的很少，下面是我摘抄的技术代码，原文地址见文章下面.

PagerFragment里面适配的fragment只需要继承自LazyFragment处理懒加载关系，而LazyFragment继承自BaseFragment，BaseFragment处理fragment初始化控件和fragment销毁时和activity分离的事情

下面献上LazyFragment的源码:

public class LazyFragment extends BaseFragment
{
private boolean isInit=false;//真正要显示的view是否已经被初始化(正常加载)
private Bundle savedInstancseState;
public static final String INTENT_BOOLEAN_LAZYLOAD="intent_boolean_lazyLoad";
private boolean isLazyLoad=true;//默认状态需要懒加载
private FrameLayout layout;
private boolean isStart=false;// 是否处于可见状态，in the screen
@override
protected final void onCreateView(Bundle savedInstancseState)
{
super.onCreateView(savedInstancseState);
Bundle bundle=getArguments();
if(bundle!=null)
{
isLazyLoad=bundle.getBoolean(INTENT_BOOLEAN_LAZYLOAD,isLazyLoad);
}
//判断是否懒加载
if(isLazyLoad)
{
//一旦isVisibleToUser==true即可对真正需要的显示内容进行加载
if(getUserVisibleHint()&&!isInint)
{
this.savedInstancseState=savedInstancseState;
onCreateViewLazy(savedInstancseState);
isInint=true;
}else{
//进行懒加载
layout=new FrameLayout(getApplicationContext);
layout.setLayoutParams(new LayoutParams(LayoutParams.MATCH_PARENT,LayoutParams.MATCH_PARENT));
View view=LayoutInflater.from(getApplicationContext()).inflate(R.layout.fragment_lazy_loading,null);
layout.addView(view);
super.setContentView(layout);
}
}else
{
//不需要懒加载，开门见山，调用onCreateViewLazy正常加载显示内容即可
onCreateViewLazy(savedInstancseState);
isInint=true;
}
}
@override
public void setUserVisibleHint(boolean isVisibleToUser)
{
super.setUserVisibleHint(isVisibleToUser);
Log.d("TAG", "setUserVisibleHint() called with: " + "isVisibleToUser = [" + isVisibleToUser + "]");
//一旦isVisibleToUser==true即可进行对真正需要的显示内容的加载
//可见，但还没被初始化
if(isVisibleToUser&&!isInint&&getContentView()!=null)
{
onCreateViewLazy(savedInstancseState);
isInint=true;
onResumeLazy();//TODO
}
//已经被初始化(正常加载)过了
if(isInint&&getContentView!=null)
{
if(isVisibleToUser)
{
isStart=true;
onFragmentStartLazy();//TODO
}else{
isStart=false;
onFragmentStopLazy();
}
}
@override
public void setContentView(int layoutResID)
{
//判断若isLazyLoad=true,移除所有lazy view，加载真正要显示的view
if(isLazyLoad&&getContentView()!=null&&getContentView().getParent()!=null)
{
layout.removeAllViews();
View view=inflater.inflate(layoutResID,layout,false);
layout.addView(view);
}else
{
super.setContentView(layoutResID);
}
}
@override
public void setContentView(View view)
{
//判断若isLazyLoad=true,移除所有lazy view，加载真正要显示的view
if(isLazyLoad&&getContentView()!=null&&getContentView().getParent!=null)
{
layout.removeAllViews();
layout.addView(view);
}else
{
//否则开门见山，直接加载
super.setContentView(view);
}
}
@override
public final void onStart()
{
Log.d("TAG", "onStart() : " + "getUserVisibleHint():" + getUserVisibleHint());
super.onStart();
if(isInit&&!isStart&&getUserVisibleHint())
{
isStart=true;
onFragmentStartLazy();
}
}
//当Fragment被滑到可见的位置时，调用
protected void onFragmentStartLazy() {
Log.d("TAG", "onFragmentStartLazy() called with: " + "");
}

@override
public final void onStop()
{
super.onStop();
if(isInit&&isStart&&getUserVisibleHint())
{
isStart=false;
onFragmentStopLazy();
}
}
@Override
@Deprecated
public final void onResume() {
Log.d("TAG", "onResume() : " + "getUserVisibleHint():" + getUserVisibleHint());
super.onResume();
if (isInit) {
onResumeLazy();
}
}
@Override
@Deprecated
public final void onResume() {
Log.d("TAG", "onResume() : " + "getUserVisibleHint():" + getUserVisibleHint());
super.onResume();
if (isInit) {
onResumeLazy();
}
}

@Override
@Deprecated
public final void onPause() {
Log.d("TAG", "onPause() : " + "getUserVisibleHint():" + getUserVisibleHint());
super.onPause();
if (isInit) {
onPauseLazy();
}
}
@Override
@Deprecated
public final void onDestroyView() {
Log.d("TAG", "onDestroyView() : " + "getUserVisibleHint():" + getUserVisibleHint());
super.onDestroyView();
if (isInit) {
onDestroyViewLazy();
}
isInit = false;
}

//当Fragment被滑到不可见的位置，offScreen时，调用
protected void onFragmentStopLazy() {
Log.d("TAG", "onFragmentStopLazy() called with: " + "");
}

protected void onCreateViewLazy(Bundle savedInstanceState) {
Log.d("TAG", "onCreateViewLazy() called with: " + "savedInstanceState = [" + savedInstanceState + "]");
}

protected void onResumeLazy() {
Log.d("TAG", "onResumeLazy() called with: " + "");
}

protected void onPauseLazy() {
Log.d("TAG", "onPauseLazy() called with: " + "");
}

protected void onDestroyViewLazy() {

}

}

Basefragment的源码如下:

public class BaseFragment extends Fragment
{
protected LayoutInflater inflater;
private View contentView;
private Context context;
private ViewGroup container;
@override
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
context=getActivity().getApplicationContext();
}
//子类通过重写onCreateView，调用setContentView进行布局设置，否者contentView==null,返回Null
@override
public final View onCreateView(LayoutInflater inflater,ViewGroup container,Bundle savedInstanceState)
{
this.inflater=inflater;
this.container=container;
onCreateView(savedInstanceState);
if(contentView==null)
return super.onCreateView(inflater,container,savedInstanceState);
return contentView;
}
protected void onCreateView(Bundle savedInstanceState)
{

}
@override
public void onDestroyView()
{
super.onDestroyView();
contentView=null;
container=null;
inflater=null;
}
public Context getApplicationContex()
{
return context;
}
public void setContentView(int layoutResID)
{
setContetnView((ViewGroup)inflater.inflate(layoutResID,container,false));
}
public void setContentView(View view)
{
contentView=view;
}
public void getContentView()
{
return contentView;
}
public View findViewById(int id)
{
if(contentView!=null)
{
return contentView.findViewById(id);
}
return null;
}
// http://stackoverflow.com/questions/15207305/getting-the-error-java-lang-illegalstateexception-activity-has-been-destroyed @Override
public void onDetach() {
Log.d("TAG", "onDetach() : ");
super.onDetach();
try {
Field childFragmentManager = Fragment.class.getDeclaredField("mChildFragmentManager");
childFragmentManager.setAccessible(true);
childFragmentManager.set(this, null);

} catch (NoSuchFieldException e) {
throw new RuntimeException(e);
} catch (IllegalAccessException e) {
throw new RuntimeException(e);
}
}

@Override
public void onDestroy() {
Log.d("TAG", "onDestroy() : ");
super.onDestroy();
}

}

亲测有效

备注:转载地址 (http://www.jianshu.com/p/8a772b9df6d5)