Android兼容之摄像头权限关闭后应用生命周期和单例数据变化-创新互联

描述：当app摄像头权限打开后，运行中的app和单例中的数据正常；切换到设置页面关闭摄像头权限后；再切换到app发生的变化
结果： activity会重新绘制，activity历史栈会保留，但是回退到历史栈的activity会重新从onCreate(***)开始；且单例中的数据被重置，例如：int 数据被重置为0，对象被重置为null

单例代码

public class CountManager {private CountManager() {}

    public static CountManager getInstance() {return SingleHolder.instance;
    }

    private static class SingleHolder {private static final CountManager instance = new CountManager();
    }

    private int mCount = 0;

    public void addCount() {mCount++;
    }

    public int getCount() {return mCount;
    }
}

第一个activity

public class MainActivity extends AppCompatActivity {private static final String TAG = "MainActivity-1";

    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_second);
        CountManager.getInstance().addCount(); //单例中数据增加
        findViewById(R.id.btn_second_click).setOnClickListener(new View.OnClickListener() {@Override
            public void onClick(View v) {startActivity(new Intent(MainActivity.this, SecondActivity.class));
            }
        });
        Log.d(TAG, "onCreate: ");
    }

    @Override
    protected void onResume() {super.onResume();
        Log.d(TAG, "onResume: " + CountManager.getInstance().getCount());
    }

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

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

第二个activity

public class SecondActivity extends AppCompatActivity {private static final String TAG = "MainActivity-Second";

    @Override
    protected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        CountManager.getInstance().addCount();
         if (savedInstanceState == null) {getSupportFragmentManager().beginTransaction()
                    .replace(R.id.container, MainFragment.newInstance())
                    .commitNow();
        }
        Log.d(TAG, "onCreate: ");
    }

    @Override
    protected void onResume() {super.onResume();
        Log.d(TAG, "onResume: "+ CountManager.getInstance().getCount());
    }

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

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

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

备注：记得app增加摄像头权限

1、启动app后，在MainActivity，点击跳转到SecondActivity

D  onCreate: 
15:28:09.177 com.xiaoma.testc                     D  onResume: 1

15:28:11.663 com.xiaoma.testc                     D  onPause: 
15:28:11.708 com.xiaoma.testc                     D  onCreate: 
15:28:11.751 com.xiaoma.testc                     D  onResume: 2

2、切换到桌面，摄像头权限进行关闭操作或者打开后再关闭

15:31:44.956 com.xiaoma.testc                     D  onPause: 
15:31:44.989 com.xiaoma.testc                     D  onStop: 
---------------------------- PROCESS ENDED (31143) for package com.xiaoma.testc ----------------------------

可以看到进程关闭了的信息
3、再次点击app，查看里面的数据，然后进行回退历史栈

---------------------------- PROCESS STARTED (32348) for package com.xiaoma.testc ----------------------------
15:32:57.135 com.xiaoma.testc                     D  onCreate: 
15:32:57.170 com.xiaoma.testc                     D  onResume: 1
15:33:13.688 com.xiaoma.testc                     D  onPause: 
//返回操作后
15:33:13.751 com.xiaoma.testc                     D  onCreate: 
15:33:13.755 com.xiaoma.testc                     D  onResume: 2
15:33:14.162 com.xiaoma.testc                     D  onStop: 
15:33:14.167 com.xiaoma.testc                     D  onDestroy:

可以看到重启启动了进程，且历史栈存在

对于开发SDK的，由于需要宿主传递接口回调，会导致回调为null，所以在页面需要进行回调判断，进行相关的业务处理。

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