Fragment_StateLoss

问题 ，Activity恢复后 mStateSaved,是怎么恢复的？

就是onSavedInstanceState 的官方API文档2

这里问题的场景是Activity已经关闭了,rpc请求很久再回来,导致了这个问题,所以我觉得判断livedate激活状态就可以了

可是这个改动应该只能在resume吧？

LiveData started 和 resumed 都可以

Livedata 会感知activity生命周期

这个有可能 activity 也在 started / resumed 状态下发出吧？ 这样的话，showDialog 应该也还会崩溃，因为onSavedInstanceState 是在 paused 时候发生的，这个时候应该还是 started 状态。

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/**

* 后续考虑做个技改把它加到[BaseDialogFragment]里面

*/

fun showWithLifecycle(fragmentActivity: FragmentActivity, tag: String? = null) {

  val liveData = showWithLifecycleLiveData ?: MutableLiveData<Boolean>().also {

    it.observe(fragmentActivity) { this.show(fragmentActivity.supportFragmentManager, tag) }

    showWithLifecycleLiveData = it

  }

  liveData.value = true

}

onSaveInstanceState保存分析

https://juejin.cn/post/6995791487426363405

状态恢复

https://www.jianshu.com/p/58579627f70a

https://juejin.cn/post/7057564670567120903

can not perform this action after onsaveinstancestate dialogfragment show

developer -> 不保留活动

onSaveInstanceState以下5种情况被调用：

1、当用户按下手机home键的时候。

2、长按手机home键或者按下菜单键时。

3、手机息屏时。

4、FirstActivity启动SecondActivity，FirstActivity就会调用，也就是说打开新Activity时，原Activity就会调用。

5、默认情况下横竖屏切换时。

打开Activity -> Home -> 再从后台拿出来

20220919212018

既然状态的保存与恢复都必须要把Fragment带上，那么一旦当Fragment的状态已保存过了，那么就不应该再改变Fragment的状态。因此FragmentManager的每一个操作前，都会调用一个方法来检查状态是否保存过了：

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private void checkStateLoss() {
    if (mStateSaved) {
        throw new IllegalStateException(
                    "Can not perform this action after onSaveInstanceState");
    }
    if (mNoTransactionsBecause != null) {
        throw new IllegalStateException(
                    "Can not perform this action inside of " + mNoTransactionsBecause);
    }
}
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/**
 * This is the same as {@link #onSaveInstanceState} but is called for activities
 * created with the attribute {@link android.R.attr#persistableMode} set to
 * <code>persistAcrossReboots</code>. The {@link android.os.PersistableBundle} passed
 * in will be saved and presented in {@link #onCreate(Bundle, PersistableBundle)}
 * the first time that this activity is restarted following the next device reboot.
 *
 * @param outState Bundle in which to place your saved state.
 * @param outPersistentState State which will be saved across reboots.
 *
 * @see #onSaveInstanceState(Bundle)
 * @see #onCreate
 * @see #onRestoreInstanceState(Bundle, PersistableBundle)
 * @see #onPause
 */
public void onSaveInstanceState(@NonNull Bundle outState,
        @NonNull PersistableBundle outPersistentState) {
    onSaveInstanceState(outState);
}

为什么会有这个异常

https://blog.csdn.net/lzf_acraftsman/article/details/108831949

https://juejin.cn/post/6844903458605105160

fragment重叠原因

Fragment懒加载

Fragment和ViewPager一起使用会有个预加载机制，会把旁白的Fragment的生命周期方法
前半段先执行，然后执行自身的生命周期方法

在项目终从其他页面回到MainAcitivty的时候，三个页面的生命周期方法都跑了一遍

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　  D/FinanceFragment         Test: onStart()
D/WealthFragment         Test: onStart()
D/MineFragment         Test: onStart()
D/FinanceFragment         Test: onResume()
D/WealthFragment         Test: onResume()
D/MineFragment         Test: onResume()
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    private boolean isPrepared;  //判断view是否加载完成,在视图未初始化的时候，在lazyLoad当中就使用的话，就会有空指针的异常
    private boolean isVisible;  //判断当前Fragment是否可见状态,标志已经初始化完成，因为setUserVisibleHint是在onCreateView之前调用的
	  @Override
    public void onViewCreated(View view, @Nullable Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);
        isPrepared = true;
        lazyLoad();
    }


    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, Bundle savedInstanceState) {
//        Log.d(TAG + "         Test", " onCreateView()");

        if (rootView == null) {
            int view = setLayoutId();
            if (view != 0) {
                rootView = inflater.inflate(view, container, false);
            }
        } else {
            ViewGroup parent = (ViewGroup) rootView.getParent();
            if (parent != null) {
                parent.removeView(rootView);
            }
        }
        initView(rootView);
        return rootView;
    }

    //  http://www.10tiao.com/html/565/201702/2247483988/1.html
    // 标志位，标志已经初始化完成，因为setUserVisibleHint是在onCreateView之前调用的，
    // 在视图未初始化的时候，在lazyLoad当中就使用的话，就会有空指针的异常
    private boolean isPrepared;
    //标志当前页面是否可见
    private boolean isVisible;

    @Override
    public void setUserVisibleHint(boolean isVisibleToUser) {
        super.setUserVisibleHint(isVisibleToUser);
//        Log.d(TAG + "         Test", " setUserVisibleHint() is Visible : ?  " + isVisibleToUser);

        if (getUserVisibleHint()) {
            isVisible = true;
            onVisible();
        } else {
            isVisible = false;
            onInvisible();
        }
    }

    protected void onInvisible() {

    }

    protected void onVisible() {
        lazyLoad();
    }

    private void lazyLoad() {
        if (!isVisible || !isPrepared) {
            return;
        }
        requestData();
    }

    /**
     * 请求数据
     */
    protected void requestData() {
        Log.d(TAG + "         Test", " requestData ");
    }


http://www.10tiao.com/html/565/201702/2247483988/1.html

Activity dialogFragment 的事件回调

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interface ISelectListener {
    fun getItemPosition(position: Int)
}

var mListener: ISelectListener? = null

override fun onAttach(context: Context) {
    super.onAttach(context)
    if (parentFragment is ISelectListener){
        mListener = parentFragment  as ISelectListener
    }else if (context is ISelectListener) {
        mListener = context
    } else {
        throw RuntimeException(context!!.toString() + " must implement ISelectListener")
    }
}

https://developer.android.com/guide/components/fragments.html

onHiddenChanged切换刷新

使用hide()/show()发现生命周期基本不执行，不过可以用到这个onHiddenChanged();

看下执行的生命周期; 从 SecondFragment 页面开始到 ->FirstFragment

07-18 15:53:25.128 7758-7758/com.mineutils D/SecondFragment: onAttach(Context context)
07-18 15:53:25.129 7758-7758/com.mineutils D/SecondFragment: onCreate()
07-18 15:53:25.142 7758-7758/com.mineutils D/SecondFragment: onCreateView()
07-18 15:53:25.148 7758-7758/com.mineutils D/SecondFragment: onViewCreated
onActivityCreated()
onStart()
​ onResume()

07-18 15:53:34.200 7758-7758/com.mineutils D/SecondFragment: onHiddenChanged hidden true
07-18 15:53:34.207 7758-7758/com.mineutils D/FirstFragment: onCreateView()
07-18 15:53:34.208 7758-7758/com.mineutils D/FirstFragment: onViewCreated
onActivityCreated()
​ onStart()

07-18 15:53:53.968 7758-7758/com.mineutils D/FirstFragment: onHiddenChanged hidden true
07-18 15:53:53.968 7758-7758/com.mineutils D/SecondFragment: onHiddenChanged hidden false

https://blog.csdn.net/cml_blog/article/details/41411451

导航栏

https://wizardforcel.gitbooks.io/w3school-android/content/77.html

https://juejin.im/post/5901b564570c35005804424b

Fragment not attached to a context

https://weidianhuang.medium.com/android-fragment-not-attached-to-a-context-24d00fac4f3d

ANDROID
#Fragment
Fragment_StateLoss
https://noteforme.github.io/2022/09/15/Fragment-StateLoss/
Author
Jon
Posted on
September 15, 2022
Licensed under