onSaveInstanceState和onRestoreInstanceState的调用

最新推荐文章于 2021-01-29 17:01:56 发布

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本文详细解析了Android中onSaveInstanceState方法的调用时机及其应用场景，包括用户操作导致的Activity状态变化，如按下Home键、电源键及屏幕方向切换等。

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package com.z.onsaveinstancestateparse;

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.util.Log;
import android.view.View;

public class MainActivity extends Activity {

	private static final String TAG = MainActivity.class.getSimpleName();

	private int saveString_int;
	private String saveString_str;

	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);
		Log.i(TAG, "-----------onCreate------------");
		if (savedInstanceState != null) {
			Log.i(TAG, "-->>onCreate:" + savedInstanceState.getInt("saveString_int"));
			Log.i(TAG, "-->>onCreate:" + savedInstanceState.getString("saveString_str"));
		}
	}

	@Override
	protected void onStart() {
		super.onStart();
		Log.i(TAG, "-----------onStart------------");
	}

	@Override
	protected void onRestart() {
		super.onRestart();
		Log.i(TAG, "-----------onRestart------------");
	}

	@Override
	protected void onResume() {
		super.onResume();
		Log.i(TAG, "-----------onResume------------");
	}

	@Override
	protected void onPause() {
		super.onPause();
		Log.i(TAG, "-----------onPause------------");
	}

	@Override
	protected void onStop() {
		super.onStop();
		Log.i(TAG, "-----------onStop------------");
	}

	@Override
	protected void onDestroy() {
		super.onDestroy();
		Log.i(TAG, "-----------onDestroy------------");
	}

	@Override
	protected void onSaveInstanceState(Bundle outState) {

		Log.i(TAG, "-----------onSaveInstanceState------------");
		saveString_int = 99;
		saveString_str = "100";

		outState.putInt("saveString_int", saveString_int);
		outState.putString("saveString_str", saveString_str);
		super.onSaveInstanceState(outState);
	}

	@Override
	protected void onRestoreInstanceState(Bundle savedInstanceState) {
		super.onRestoreInstanceState(savedInstanceState);
		Log.i(TAG, "-----------onRestoreInstanceState------------");

		Log.i(TAG, "-->>onRestoreInstanceState:" + savedInstanceState.getInt("saveString_int"));
		Log.i(TAG, "-->>onRestoreInstanceState:" + savedInstanceState.getString("saveString_str"));
	}

	public void btn_jump(View v) {
		startActivity(new Intent(getApplicationContext(), TwoActivity.class));
	}
}

1.我们先开启程序,然后按home键

12-12 14:36:15.070: I/MainActivity(13358): -----------onCreate------------
12-12 14:36:15.070: I/MainActivity(13358): -----------onStart------------
12-12 14:36:15.070: I/MainActivity(13358): -----------onResume------------
12-12 14:36:22.970: I/MainActivity(13358): -----------onPause------------
12-12 14:36:23.100: I/MainActivity(13358): -----------onSaveInstanceState------------
12-12 14:36:23.100: I/MainActivity(13358): -----------onStop------------

onSaveInstanceState方法的调用是在生命周期onPause与onStop之间。然后亮屏

12-12 14:40:03.300: I/MainActivity(13358): -----------onRestart------------
12-12 14:40:03.300: I/MainActivity(13358): -----------onStart------------
12-12 14:40:03.310: I/MainActivity(13358): -----------onResume------------

2.我们先开始程序,然后按关机键，解锁亮屏

12-12 14:42:22.590: I/MainActivity(14552): -----------onCreate------------
12-12 14:42:22.590: I/MainActivity(14552): -----------onStart------------
12-12 14:42:22.590: I/MainActivity(14552): -----------onResume------------
12-12 14:42:25.890: I/MainActivity(14552): -----------onPause------------
12-12 14:42:25.890: I/MainActivity(14552): -----------onSaveInstanceState------------
12-12 14:42:25.890: I/MainActivity(14552): -----------onStop------------
12-12 14:42:28.570: I/MainActivity(14552): -----------onRestart------------
12-12 14:42:28.570: I/MainActivity(14552): -----------onStart------------
12-12 14:42:28.580: I/MainActivity(14552): -----------onResume------------

3.开始程序,跳转另一个activity,然后在返回

12-12 14:44:42.660: I/MainActivity(14886): -----------onCreate------------
12-12 14:44:42.660: I/MainActivity(14886): -----------onStart------------
12-12 14:44:42.660: I/MainActivity(14886): -----------onResume------------
12-12 14:44:44.940: I/MainActivity(14886): -----------onPause------------
12-12 14:44:45.090: I/MainActivity(14886): -----------onSaveInstanceState------------
12-12 14:44:45.090: I/MainActivity(14886): -----------onStop------------
12-12 14:44:51.250: I/MainActivity(14886): -----------onRestart------------
12-12 14:44:51.250: I/MainActivity(14886): -----------onStart------------
12-12 14:44:51.250: I/MainActivity(14886): -----------onResume------------

这里其实1、2、3生命周期的是一样的

4.开始程序,横屏在恢复竖屏。

12-12 14:48:07.820: I/MainActivity(15372): -----------onCreate------------
12-12 14:48:07.820: I/MainActivity(15372): -----------onStart------------
12-12 14:48:07.820: I/MainActivity(15372): -----------onResume------------
12-12 14:48:14.000: I/MainActivity(15372): -----------onPause------------
12-12 14:48:14.000: I/MainActivity(15372): -----------onSaveInstanceState------------
12-12 14:48:14.000: I/MainActivity(15372): -----------onStop------------
12-12 14:48:14.000: I/MainActivity(15372): -----------onDestroy------------
12-12 14:48:14.080: I/MainActivity(15372): -----------onCreate------------
12-12 14:48:14.080: I/MainActivity(15372): -->>onCreate:99
12-12 14:48:14.080: I/MainActivity(15372): -->>onCreate:100
12-12 14:48:14.080: I/MainActivity(15372): -----------onStart------------
12-12 14:48:14.080: I/MainActivity(15372): -----------onRestoreInstanceState------------
12-12 14:48:14.080: I/MainActivity(15372): -->>onRestoreInstanceState:99
12-12 14:48:14.080: I/MainActivity(15372): -->>onRestoreInstanceState:100
12-12 14:48:14.080: I/MainActivity(15372): -----------onResume------------
12-12 14:48:17.570: I/MainActivity(15372): -----------onPause------------
12-12 14:48:17.570: I/MainActivity(15372): -----------onSaveInstanceState------------
12-12 14:48:17.570: I/MainActivity(15372): -----------onStop------------
12-12 14:48:17.570: I/MainActivity(15372): -----------onDestroy------------
12-12 14:48:17.630: I/MainActivity(15372): -----------onCreate------------
12-12 14:48:17.630: I/MainActivity(15372): -->>onCreate:99
12-12 14:48:17.630: I/MainActivity(15372): -->>onCreate:100
12-12 14:48:17.630: I/MainActivity(15372): -----------onStart------------
12-12 14:48:17.630: I/MainActivity(15372): -----------onRestoreInstanceState------------
12-12 14:48:17.630: I/MainActivity(15372): -->>onRestoreInstanceState:99
12-12 14:48:17.630: I/MainActivity(15372): -->>onRestoreInstanceState:100
12-12 14:48:17.630: I/MainActivity(15372): -----------onResume------------

onSaveInstanceState方法会在什么时候被执行，有这么几种情况：

1、当用户按下HOME键时。

这是显而易见的，系统不知道你按下HOME后要运行多少其他的程序，自然也不知道activity A是否会被销毁，故系统会调用onSaveInstanceState，让用户有机会保存某些非永久性的数据。以下几种情况的分析都遵循该原则

2、长按HOME键，选择运行其他的程序时。

3、按下电源按键（关闭屏幕显示）时。

4、从activity A中启动一个新的activity时。

5、屏幕方向切换时，例如从竖屏切换到横屏时。

在屏幕切换之前，系统会销毁activity A，在屏幕切换之后系统又会自动地创建activity A，所以onSaveInstanceState一定会被执行

总而言之，onSaveInstanceState的调用遵循一个重要原则，即当系统“未经你许可”时销毁了你的activity，则onSaveInstanceState会被系统调用，这是系统的责任，因为它必须要提供一个机会让你保存你的数据（当然你不保存那就随便你了）。

至于onRestoreInstanceState方法，需要注意的是，onSaveInstanceState方法和onRestoreInstanceState方法“不一定”是成对的被调用的，onRestoreInstanceState被调用的前提是，activity A“确实”被系统销毁了，而如果仅仅是停留在有这种可能性的情况下，则该方法不会被调用，例如，当正在显示activity A的时候，用户按下HOME键回到主界面，然后用户紧接着又返回到activity A，这种情况下activity A一般不会因为内存的原因被系统销毁，故activity A的onRestoreInstanceState方法不会被执行

另外，onRestoreInstanceState的bundle参数也会传递到onCreate方法中，你也可以选择在onCreate方法中做数据还原

参考： http://blog.youkuaiyun.com/lccly/article/details/6089667