的onCreate（...）被调用两次设备旋转后 [英] onCreate(...) is called twice after the device is rotated

问题描述

我有一个关于旋转Android设备的问题。我的code将记录静态和非静态的属性中的onCreate（...）。

进口android.app.Activity; 进口android.os.Bundle; 进口android.util.Log; 公共类MainActivity延伸活动{     静态INT SN;     INT N;     @覆盖     公共无效的onCreate（包savedInstanceState）{         super.onCreate（savedInstanceState）;         的setContentView（R.layout.main）;         SN ++;         ñ++;         Log.i（的onCreate的String.Format（SN =％DN =％D，SN，N））;     } }

屏幕方向是纵向。当我第一次跑了code，我得到了：

 的onCreate（）：SN = 1 N = 1
 

在我旋转屏幕为横向，我得到了：

 的onCreate（）：SN = 2 N = 1
 

在我再次旋转屏幕为纵向，我得到了：

 的onCreate（）：SN = 3 N = 1
的onCreate（）：SN = 4 N = 1
 

我的问题是：

1. 如何prevent的onCreate（...）被调用两次当设备旋转回肖像？
2. 如何保存非静态变量的值时，该设备旋转？

解决方案

每当屏幕方向改变时，该活动被破坏，新的活动开始由的onCreate（）方法。 所以每次旋转屏幕，活动会被破坏，新的活动开始由的onCreate（）方法。 您可以通过覆盖的onSaveInstanceState（包B）方法保存非静态成员。 Android把这种方法每当屏幕旋转，并且，鉴于叠B将被传递给的OnCreate（束B）从中可以提取您的非静态成员。

I have a question about rotating the Android device. My code logs a static and non-static attribute in onCreate(...).

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

public class MainActivity extends Activity {
    static int sn;
    int n;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        sn++;
        n++;

        Log.i("onCreate", String.format("sn=%d n=%d", sn, n));
    }
}

The screen orientation is portrait. When I first ran the code, I got:

onCreate(): sn=1 n=1

After I rotated the screen to landscape, I got:

onCreate(): sn=2 n=1

After I rotated the screen again to portrait, I got:

onCreate(): sn=3 n=1
onCreate(): sn=4 n=1

My questions are:

1. How can I prevent onCreate(...) to be called twice when the device is rotated back to portrait?
2. How can I save the value of non-static variable when the device is rotated?

解决方案

Whenever the screen orientation is changed, that Activity is destroyed and a new activity starts by onCreate() method. so every time you rotate the screen that activity will be destroyed and a new activity starts by onCreate() method. You can save Non Static member by overriding onSaveInstanceState(Bundle b) method. Android calls this method whenever the screen is rotated, and that given bundle b would be passed to oncreate(Bundle b) from which you can extract your non static member.

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