Android 动态申请权限

     public class Main2Activity extends AppCompatActivity {
        private static final int MY_PERMISSIONS_REQUEST = 1001;

        private ImageView ivMusic;
        private SurfaceView surfaceView;
        private Button btnCamera;
        private SurfaceView cammerSurfaceView;
        private Camera camera;


        /**
           * 需要申请的运行时权限
         */
        private String[] permissions = new String[]{
             Manifest.permission.CAMERA,
             Manifest.permission.WRITE_EXTERNAL_STORAGE
        };
        /**
         * 被用户拒绝的权限列表
         */
        private List<String> mPermissionList = new ArrayList<>();

        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main2);
            checkPermissions();

            btnCamera = (Button) findViewById(R.id.btn_camera);
            btnCamera.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    onCamera();
                }
            });
            cammerSurfaceView = (SurfaceView) findViewById(R.id.suface_view);

            camera = Camera.open();
            camera.setDisplayOrientation(90);   // 打开摄像头并将展示方向旋转90度
        }

        private void onCamera(){
            cammerSurfaceView.getHolder().addCallback(new SurfaceHolder.Callback() {
                @Override
                public void surfaceCreated(SurfaceHolder holder) {
                    try {
                        camera.setPreviewDisplay(holder);
                        camera.startPreview();
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
  
                }

                @Override
                public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {

                }

                @Override
                public void surfaceDestroyed(SurfaceHolder holder) {
                    camera.stopPreview();
                    camera.release();
                    camera = null;
                }
            });
        }

        @Override
        public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {
            if (requestCode == MY_PERMISSIONS_REQUEST) {
                for (int i = 0; i < grantResults.length; i++) {
                    if (grantResults[i] != PackageManager.PERMISSION_GRANTED) {
                        Log.i("-->", permissions[i] + " 权限被用户禁止！");
                    }
                }
                // 运行时权限的申请不是本demo的重点，所以不再做更多的处理，请同意权限申请。
            }
        }
        private void checkPermissions() {
            // Marshmallow开始才用申请运行时权限
            if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
                for (int i = 0; i < permissions.length; i++) {
                    if (ContextCompat.checkSelfPermission(this, permissions[i]) !=
                        PackageManager.PERMISSION_GRANTED) {
                        mPermissionList.add(permissions[i]);
                    }
                }
                if (!mPermissionList.isEmpty()) {
                    String[] permissions = mPermissionList.toArray(new String[mPermissionList.size()]);
                    ActivityCompat.requestPermissions(this, permissions, MY_PERMISSIONS_REQUEST);
                }
            }
        }
    }