最近项目做优化,主页面用的是viewpager + Fragment 实现。发现每次启动应用后,就会有其他页面会发起接口请求,这点很不好。虽然说可以提前加载其他页面的数据,但是会在某一短时间内发起很多的请求,加大内存的消耗。同时,这样也不合使用习惯,页面还没有看见就发起了请求,加载了页面。
最后解决办法使用Fragment 的 setUserVisibleHint 的方法,解释如下:
/**
* Set a hint to the system about whether this fragment's UI is currently visible
* to the user. This hint defaults to true and is persistent across fragment instance
* state save and restore.
*
* <p>An app may set this to false to indicate that the fragment's UI is
* scrolled out of visibility or is otherwise not directly visible to the user.
* This may be used by the system to prioritize operations such as fragment lifecycle updates
* or loader ordering behavior.</p>
*
* @param isVisibleToUser true if this fragment's UI is currently visible to the user (default),
* false if it is not.
*/
</pre><pre name="code" class="html"> <pre name="code" class="html"> @Override
public void setUserVisibleHint(boolean isVisibleToUser) {
super.setUserVisibleHint(isVisibleToUser);
if (isVisibleToUser) {// onResume
mIsResume = true;
isVisible = true;
lazyLoad();
} else {// onPause
isVisible = false;
}
}
public abstract void lazyLoad();
/**
* 标志位,标志已经初始化完成
*/
private boolean isPrepared;
/**
* 是否已被加载过一次,第二次就不再去请求数据了
*/
private boolean mHasLoadedOnce;
</pre><pre name="code" class="html"> <pre name="code" class="html">public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
super.onCreateView(inflater, container, savedInstanceState);
View view = inflater.inflate(R.layout.fragment_base_listview, null);
isPrepared = true;
return view;
}
@Override
public void lazyLoad() {
super.lazyLoad();
LogUtils.d(TAG, "lazyload isPrepared = " + isPrepared + " isVisible == " + isVisible + " mHasLoadedOnce == " + mHasLoadedOnce);
if (!isPrepared || !isVisible || mHasLoadedOnce) {
return;
}
if (null != mAdapter && mAdapter.getCount() == 0 && mLoadOver && needRequest()) {
LogUtils.d(TAG, " initData--->");
mPtrFrame.postDelayed(new Runnable() {
@Override
public void run() {
mHasLoadedOnce = true;
mPtrFrame.autoRefresh();
}
}, 100);
}
}
由于页面的嵌套很深, 还遇到了一种情况。项目最外层结构是Viewpager + Fragment 。 但是在一个Fragment 中又有 FragmentA, FragmentB。 其中FragmentA 包含 Viewpager + Fragment。 这里面子FragmentC 还包含两种样式的布局。在这种情况下,最里层Fragment的 <span style="font-family: Arial, Helvetica, sans-serif;">getUserVisibleHint()为false。但是我们可以通过判断parentFragment的状态还判断子Fragment的。</span>
<span style="font-family: Arial, Helvetica, sans-serif;"> </span><pre name="code" class="html"> android.support.v4.app.Fragment parentFragment = getParentFragment();
if(parentFragment != null){
if(parentFragment.getUserVisibleHint()){
isVisible = true;
LogUtils.d(TAG, " isVisible = true");
}
}
当activity 里加载Fragment ,此时判断fragment 的 getUserVisibleHint()为false, 需要手动的设为true。