public class LazyFragment extends Fragment { private View mRootView;
private boolean mIsInited;
private boolean mIsPrepared; @Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
mRootView = inflater.inflate(R.layout.fragment_lazy, container, false);
mIsPrepared = true;
lazyLoad();
return mRootView;
}
public void lazyLoad() {
if (getUserVisibleHint() && mIsPrepared && !mIsInited) {
//異步初始化彼宠，在初始化后顯示正常UI
loadData();
}
}
private void loadData() {
new Thread() {
public void run() {
//1. 加載數(shù)據(jù)
//2. 更新UI
//3. mIsInited = true
}
}.start();
}
@Override
public void setUserVisibleHint(boolean isVisibleToUser) {
super.setUserVisibleHint(isVisibleToUser);
if (isVisibleToUser) {
lazyLoad();
}
}
public static LazyFragment newInstance() {
return new LazyFragment();
}
}
注意點：
在Fragment中有兩個變量控制是否需要做數(shù)據(jù)加載：
mIsPrepared：表示UI是否準(zhǔn)備好煤蹭，因為數(shù)據(jù)加載后需要更新UI复濒，如果UI還沒有inflate赎瞎，就不需要做數(shù)據(jù)加載，因為setUserVisibleHint()會在onCreateView()之前調(diào)用一次，如果此時調(diào)用，UI還沒有inflate，因此不能加載數(shù)據(jù)链烈。
mIsInited：表示是否已經(jīng)做過數(shù)據(jù)加載，如果做過了就不需要做了挚躯。因為setUserVisibleHint(true)在界面可見時都會調(diào)用强衡，如果滑到該界面做過數(shù)據(jù)加載后，滑走码荔，再滑回來食侮，還是會調(diào)用setUserVisibleHint(true)，此時由于mIsInited=true目胡，因此不會再做一遍數(shù)據(jù)加載锯七。
lazyLoad()：懶加載的核心類，在該方法中誉己，只有界面可見（getUserVisibleHint()==true）眉尸、UI準(zhǔn)備好（mIsPrepared==true）、過去沒做過數(shù)據(jù)加載（mIsInited==false）時，才需要調(diào)loadData()做數(shù)據(jù)加載噪猾，數(shù)據(jù)加載做完后把mIsInited置為true霉祸。
布局XML主要分兩個container，一個是初始顯示的狀態(tài)袱蜡，即R.id.container_empty丝蹭，當(dāng)數(shù)據(jù)加載完成，就顯示R.id.container：
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical" android:layout_width="match_parent"
android:layout_height="match_parent">
<RelativeLayout
android:id="@+id/container_empty"
android:layout_width="match_parent"
android:layout_height="match_parent">
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_centerInParent="true"
android:text="正在加載"
/>
</RelativeLayout>
<RelativeLayout
android:id="@+id/container"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:visibility="gone"
>
...
</RelativeLayout>
</FrameLayout>
最后附上我改的懶加載類
package cn.qssq666.quickdevelopframe.base.fragment;
import android.os.Bundle;
import android.support.annotation.Nullable;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
/**
* Created by qssq on 2017/11/14 qssq666@foxmail.com
*/
public abstract class LazyFragment extends Fragment {
public View getRootView() {
return mRootView;
}
private View mRootView;
private boolean mIsInited;
private boolean mIsPrepared;
public View onCreateViewFix(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
return inflater.inflate(getLayoutID(), container, false);
}
@Override
public final View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
mRootView = onCreateViewFix(inflater, container, savedInstanceState);
mIsPrepared = true;
lazyLoad(inflater, container);
return mRootView;
}
public void lazyLoad(LayoutInflater inflater, ViewGroup container) {
if (getUserVisibleHint() && mIsPrepared && !mIsInited) {
//異步初始化坪蚁，在初始化后顯示正常UI
init(inflater, container);
mIsInited = true;
}
}
//1. 加載數(shù)據(jù)
//2. 更新UI
//3. mIsInited = true
public abstract void init(LayoutInflater inflater, ViewGroup container);
@Override
public void setUserVisibleHint(boolean isVisibleToUser) {
super.setUserVisibleHint(isVisibleToUser);
if (isVisibleToUser) {
lazyLoad(null, null);
}
}
@Override
public void onDestroyView() {
super.onDestroyView();
if (getRootView() != null) {
ViewGroup viewGroup = ((ViewGroup) getRootView());
if (viewGroup != null) {
viewGroup.removeView(getRootView());
}
}
}
protected abstract int getLayoutID();
}
懶加載有一個嚴(yán)重的bug,我至今沒搞出來奔穿，第一個fragment 會空白，第一次不會敏晤，再次切換的時候空白了.
參考文獻(xiàn)
入門(https://www.raywenderlich.com/169885/android-fragments-tutorial-introduction-2)
教程1
(http://assets.en.oreilly.com/1/event/68/Fragments%20for%20All%20Presentation.pdf)
教程2
(http://vinsol.com/blog/2014/09/15/advocating-fragment-oriented-applications-in-android/)
生命周期(https://github.com/xxv/android-lifecycle)
detach vs remove
Google I/O 2016: What the Fragment?(https://www.youtube.com/watch?v=k3IT-IJ0J98)
Google I/O 2017: Fragment Tricks
(https://www.youtube.com/watch?v=eUG3VWnXFtg)
mAdded和mActive的區(qū)別(https://stackoverflow.com/questions/25695960/difference-between-madded-mactive-in-source-code-of-support-fragmentmanager)
如何避免IllegalStateException異常(http://www.androiddesignpatterns.com/2013/08/fragment-transaction-commit-state-loss.html)
