为什么片段无法转动过程中收到一个非空savedInstanceState包，如果是通过XML创建？ [英] Why Fragment unable receive a non-null savedInstanceState bundle during rotation, if it is created through XML?

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问题描述

我有以下几个非常简单的片段。

UiFragment.java 

 包com.example.test;进口android.os.Bundle;
进口android.util.Log;
进口android.view.LayoutInflater;
进口android.view.View;
进口android.view.ViewGroup;进口com.actionbarsherlock.app.SherlockFragment;/ **
 *这是显示的用户界面，将工作进行更新完成片段
 *在保留片段。
 * /
公共类UiFragment扩展SherlockFragment {
    @覆盖
    公共无效onActivityCreated（捆绑savedInstanceState）{
        Log.i（卓，UiFragment onActivityCreated）;        super.onActivityCreated（savedInstanceState）;
    }    @覆盖
    公共查看onCreateView（LayoutInflater充气器，容器的ViewGroup，
            捆绑savedInstanceState）{
        Log.i（卓，UiFragment onCreateView）;        视图V = inflater.inflate（R.layout.uifragment，集装箱，FALSE）;        返回伏;
    }    @覆盖
    公共无效的onCreate（捆绑savedInstanceState）{
        Log.i（卓，UiFragment的onCreate）;        super.onCreate（savedInstanceState）;        如果（savedInstanceState！= NULL）{
            Log.i（卓， - ＆GT; UiFragment能够得到savedInstanceState的数据：+ savedInstanceState.getInt（值））;
        }
    }    @覆盖
    公共无效的onSaveInstanceState（捆绑outState）{
        super.onSaveInstanceState（outState）;
        outState.putInt（价值，111222）;
    }
}

uifragment.xml 

 ＆LT;？XML版本=1.0编码=UTF-8＆GT？;
＆LT; LinearLayout中的xmlns：机器人=htt​​p://schemas.android.com/apk/res/android
    机器人：方向=垂直
    机器人：layout_width =match_parent
    机器人：layout_height =WRAP_CONTENT
    机器人：填充=8DP＆GT;    ＆LT;的TextView
        机器人：layout_width =WRAP_CONTENT
        机器人：layout_height =WRAP_CONTENT
        机器人：layout_gravity =中心
        机器人：textAppearance =机器人：ATTR / textAppearanceMedium
        机器人：文字=fragment_retain_instance_msg/＆GT;＆LT; / LinearLayout中＆GT;

我意识到，如果我是它通过Java code重视FragmentActivity。

MainActivity.java 

 包com.example.test;进口android.os.Bundle;
进口android.util.Log;进口com.actionbarsherlock.app.SherlockFragmentActivity;公共类MainActivity扩展SherlockFragmentActivity {    @覆盖
    保护无效的onCreate（捆绑savedInstanceState）{
        Log.i（卓，MainActivity的onCreate）;        super.onCreate（savedInstanceState）;        如果（savedInstanceState！= NULL）{
            Log.i（卓， - ＆GT; MainActivity能够得到savedInstanceState的数据：+ savedInstanceState.getInt（值））;
        }        //？
        //setContentView(R.layout.activity_main）;        如果（savedInstanceState == NULL）{
            getSupportFragmentManager（）调用BeginTransaction（）。添加（android.R.id.content，
                新UiFragment（））提交（）。
        }
    }    @覆盖
    公共无效的onSaveInstanceState（捆绑outState）{
        super.onSaveInstanceState（outState）;
        outState.putInt（价值，888999）;
    }
}

每次当我在片段能够得到非空 savedInstanceState >的onCreate 

  02-26 00：36：48.777：I /卓（17740）：MainActivity的onCreate
02-26 00：36：48.812：I /卓（17740）：UiFragment的onCreate
02-26 00：36：49.031：I /卓（17740）：UiFragment onCreateView
02-26 00：36：49.035：I /卓（17740）：UiFragment onActivityCreated
[旋转这里发生]
02-26 00：37：37.472：I /卓（17740）：MainActivity的onCreate
02-26 00：37：37.472：I /卓（17740）：UiFragment的onCreate
02-26 00：37：37.472：I /卓（17740）： - ＆GT; UiFragment能够得到savedInstanceState的数据：111222
02-26 00：37：37.472：I /卓（17740）： - ＆GT; MainActivity能够得到savedInstanceState的数据：888999
02-26 00：37：37.511：I /卓（17740）：UiFragment onCreateView
02-26 00：37：37.511：I /卓（17740）：UiFragment onActivityCreated

但是，如果我更换code在 MainActivity 的的onCreate 

 如果（savedInstanceState == NULL）{
    getSupportFragmentManager（）调用BeginTransaction（）。添加（android.R.id.content，
        新UiFragment（））提交（）。
}

通过XML片断创建

 的setContentView（R.layout.activity_main）;

activity_main.xml中

 ＆LT;的RelativeLayout的xmlns：机器人=htt​​p://schemas.android.com/apk/res/android
    的xmlns：工具=htt​​p://schemas.android.com/tool​​s
    机器人：layout_width =match_parent
    机器人：layout_height =match_parent
    机器人：paddingBottom会=@扪/ activity_vertical_margin
    机器人：paddingLeft =@扪/ activity_horizo​​ntal_margin
    机器人：paddingRight =@扪/ activity_horizo​​ntal_margin
    机器人：paddingTop =@扪/ activity_vertical_margin
    工具：上下文=MainActivity。＆GT;    ＆LT;片段类=com.example.test.UiFragment
        机器人：layout_width =match_parent
        机器人：layout_height =match_parent/＆GT;＆LT; / RelativeLayout的＆GT;

我会得到以下日志，当我进行旋转。

  02-26 00：39：23.437：I /卓（18055）：MainActivity的onCreate
02-26 00：39：23.734：I /卓（18055）：UiFragment的onCreate
02-26 00：39：23.734：I /卓（18055）：UiFragment onCreateView
02-26 00：39：23.754：I /卓（18055）：UiFragment onActivityCreated
[旋转这里发生]
02-26 00：39：27.703：I /卓（18055）：MainActivity的onCreate
02-26 00：39：27.703：I /卓（18055）： - ＆GT; MainActivity能够得到savedInstanceState的数据：888999
02-26 00：39：27.746：I /卓（18055）：UiFragment的onCreate
02-26 00：39：27.746：I /卓（18055）：UiFragment onCreateView
02-26 00：39：27.750：I /卓（18055）：UiFragment onActivityCreated

为什么在片段等行为的区别？ 为什么片段收不到旋转过程中一个非空savedInstanceState束，如果是通过XML创建？


解决方案

  

被实例化的片段必须有某种独特的
  标识符，以便它可以与previous例如，如果重新关联
  父活动需要被破坏并重新创建。这可以是
  提供这些方式：


供应ID，以片段XML标签解决问题。

 ＆LT;片段类=com.example.test.UiFragment
    机器人：ID =@ + ID / myFragment
    机器人：layout_width =match_parent
    机器人：layout_height =match_parent/＆GT;

I have the following very simple Fragment.

UiFragment.java

package com.example.test;

import android.os.Bundle;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

import com.actionbarsherlock.app.SherlockFragment;

/**
 * This is a fragment showing UI that will be updated from work done
 * in the retained fragment.
 */
public class UiFragment extends SherlockFragment {


    @Override
    public void onActivityCreated(Bundle savedInstanceState) {
        Log.i("CHEOK", "UiFragment onActivityCreated");

        super.onActivityCreated(savedInstanceState);
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        Log.i("CHEOK", "UiFragment onCreateView");

        View v = inflater.inflate(R.layout.uifragment, container, false);

        return v;
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        Log.i("CHEOK", "UiFragment onCreate");

        super.onCreate(savedInstanceState);

        if (savedInstanceState != null) {
            Log.i("CHEOK", "--> UiFragment able get savedInstanceState's data : " + savedInstanceState.getInt("value"));
        }       
    }

    @Override
    public void onSaveInstanceState(Bundle outState) {
        super.onSaveInstanceState(outState);
        outState.putInt("value", 111222);        
    }    
}

uifragment.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:padding="8dp">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center"
        android:textAppearance="?android:attr/textAppearanceMedium"
        android:text="fragment_retain_instance_msg" />

</LinearLayout>

I realize if I were attach it to FragmentActivity through Java code.

MainActivity.java

package com.example.test;

import android.os.Bundle;
import android.util.Log;

import com.actionbarsherlock.app.SherlockFragmentActivity;

public class MainActivity extends SherlockFragmentActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        Log.i("CHEOK", "MainActivity onCreate");

        super.onCreate(savedInstanceState);

        if (savedInstanceState != null) {
            Log.i("CHEOK", "--> MainActivity able get savedInstanceState's data : " + savedInstanceState.getInt("value"));
        }

        // ???
        //setContentView(R.layout.activity_main);

        if (savedInstanceState == null) {
            getSupportFragmentManager().beginTransaction().add(android.R.id.content,
                new UiFragment()).commit();
        }       
    }

    @Override
    public void onSaveInstanceState(Bundle outState) {
        super.onSaveInstanceState(outState);
        outState.putInt("value", 888999);        
    }   
}

Everytime when I perform rotation, my Fragment able to get non-null savedInstanceState during onCreate

02-26 00:36:48.777: I/CHEOK(17740): MainActivity onCreate
02-26 00:36:48.812: I/CHEOK(17740): UiFragment onCreate
02-26 00:36:49.031: I/CHEOK(17740): UiFragment onCreateView
02-26 00:36:49.035: I/CHEOK(17740): UiFragment onActivityCreated
[Rotation happens here]
02-26 00:37:37.472: I/CHEOK(17740): MainActivity onCreate
02-26 00:37:37.472: I/CHEOK(17740): UiFragment onCreate
02-26 00:37:37.472: I/CHEOK(17740): --> UiFragment able get savedInstanceState's data : 111222
02-26 00:37:37.472: I/CHEOK(17740): --> MainActivity able get savedInstanceState's data : 888999
02-26 00:37:37.511: I/CHEOK(17740): UiFragment onCreateView
02-26 00:37:37.511: I/CHEOK(17740): UiFragment onActivityCreated

However, if I were replace the code in MainActivity's onCreate

if (savedInstanceState == null) {
    getSupportFragmentManager().beginTransaction().add(android.R.id.content,
        new UiFragment()).commit();
}

with fragment creation through XML

setContentView(R.layout.activity_main);

activity_main.xml

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context=".MainActivity" >

    <fragment class="com.example.test.UiFragment"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />

</RelativeLayout>

I will get the following log when I perform rotation.

02-26 00:39:23.437: I/CHEOK(18055): MainActivity onCreate
02-26 00:39:23.734: I/CHEOK(18055): UiFragment onCreate
02-26 00:39:23.734: I/CHEOK(18055): UiFragment onCreateView
02-26 00:39:23.754: I/CHEOK(18055): UiFragment onActivityCreated
[Rotation happens here]
02-26 00:39:27.703: I/CHEOK(18055): MainActivity onCreate
02-26 00:39:27.703: I/CHEOK(18055): --> MainActivity able get savedInstanceState's data : 888999
02-26 00:39:27.746: I/CHEOK(18055): UiFragment onCreate
02-26 00:39:27.746: I/CHEOK(18055): UiFragment onCreateView
02-26 00:39:27.750: I/CHEOK(18055): UiFragment onActivityCreated

Why there is such difference in Fragment behavior? Why Fragment unable receive a non-null savedInstanceState bundle during rotation, if it is created through XML?

解决方案

The fragment being instantiated must have some kind of unique identifier so that it can be re-associated with a previous instance if the parent activity needs to be destroyed and recreated. This can be provided these ways:

Supplying id to fragment XML tag solve the problem.

<fragment class="com.example.test.UiFragment"
    android:id="@+id/myFragment"
    android:layout_width="match_parent"
    android:layout_height="match_parent" />

这篇关于为什么片段无法转动过程中收到一个非空savedInstanceState包，如果是通过XML创建？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！

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