简书链接:腾讯bugly文章fragment懒加载代码
文章字数:596,阅读全文大约需要2分钟
原文: https://mp.weixin.qq.com/mp/profile_ext?action=home&__biz=MzA3NTYzODYzMg==&scene=124&#wechat_redirect

plaintext
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
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) {
//异步初始化,在初始化后显示正常UI
loadData();
}
}

private void loadData() {
new Thread() {
public void run() {
//1. 加载数据
//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();
}
}

注意点:

在Fragment中有两个变量控制是否需要做数据加载:

mIsPrepared:表示UI是否准备好,因为数据加载后需要更新UI,如果UI还没有inflate,就不需要做数据加载,因为setUserVisibleHint()会在onCreateView()之前调用一次,如果此时调用,UI还没有inflate,因此不能加载数据。

mIsInited:表示是否已经做过数据加载,如果做过了就不需要做了。因为setUserVisibleHint(true)在界面可见时都会调用,如果滑到该界面做过数据加载后,滑走,再滑回来,还是会调用setUserVisibleHint(true),此时由于mIsInited=true,因此不会再做一遍数据加载。

lazyLoad():懒加载的核心类,在该方法中,只有界面可见(getUserVisibleHint()==true)、UI准备好(mIsPrepared==true)、过去没做过数据加载(mIsInited==false)时,才需要调loadData()做数据加载,数据加载做完后把mIsInited置为true。

布局XML主要分两个container,一个是初始显示的状态,即R.id.container_empty,当数据加载完成,就显示R.id.container:

plaintext
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
<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="正在加载"
/>

</RelativeLayout>
<RelativeLayout
android:id="@+id/container"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:visibility="gone"
>
...
</RelativeLayout>
</FrameLayout>

最后附上我改的懒加载类

plaintext
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
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) {
//异步初始化,在初始化后显示正常UI
init(inflater, container);
mIsInited = true;
}
}

//1. 加载数据
//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();
}

懒加载有一个严重的bug,我至今没搞出来,第一个fragment 会空白,第一次不会,再次切换的时候空白了.

参考文献

入门(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

(https://stackoverflow.com/questions/9156406/whats-the-difference-between-detaching-a-fragment-and-removing-it)

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的区别(https://stackoverflow.com/questions/25695960/difference-between-madded-mactive-in-source-code-of-support-fragmentmanager)

如何避免IllegalStateException异常(http://www.androiddesignpatterns.com/2013/08/fragment-transaction-commit-state-loss.html)