没有UI的Fragment的妙用——截屏

最近测试了一下Android的截图工具，最开始是这么设计的：

public class ScreenCaptor{    public static final int REQUEST_CAPTURE = 4;    public interface OnCaptureFinishedListener {        void onCaptureSuccess(Bitmap bitmap);        void onCaptureFailure();    }    public void startCapture(int requestCode, OnCaptureFinishedListener onCaptureFinishedListener) {        //...    }    public void setOnCaptureGranted(int resultCode, Intent resultData) {        //...    }}// 在Activity中使用时：public class ScreenCaptorTestActivity extends AppCompatActivity implements ScreenCaptor.OnCaptureFinishedListener {    private ScreenCaptor mScreenCaptor;    private ImageView mImageView;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_api_shot);        mImageView = findViewById(R.id.image_view);        mScreenCaptor = new ScreenCaptor(this);    }    public void onClick(View view) {        switch (view.getId()) {            case R.id.start_capture:                mScreenCaptor.startCapture(REQUEST_CAPTURE,this);                break;        }    }    @Override    protected void onActivityResult(int requestCode, int resultCode, Intent data) {        if (requestCode == REQUEST_CAPTURE) {            mScreenCaptor.setOnCaptureGranted(resultCode,data);        }    }    @Override    public void onCaptureSuccess(Bitmap bitmap) {        mImageView.setImageBitmap(bitmap);    }    @Override    public void onCaptureFailure() {    }}

因为截图需要请求权限，在使用截图工具的Activity中都要重写onActivityResult(int,int,Intent)方法，调用ScreenCaptor的setOnCaptureGranted(int,Intent)。由此想到Fragment中也有onActivityResult方法，Fragment有不带UI的用法。于是截图工具可以这样做：

public class ScreenCaptureFragment extends Fragment {    private static final String TAG = "ScreenCaptureFragment";    private static final int REQUEST_CAPTURE = 2;    public interface OnCaptureFinishedListener {        void onCaptureSuccess(Bitmap bitmap);        void onCaptureFailure();    }    private OnCaptureFinishedListener mOnCaptureFinishedListener;    private MediaProjectionManager mMediaProjectionManager;    private int mScreenWidth;    private int mScreenHeight;    private int mScreenDensity;    private ImageReader mImageReader;    private MediaProjection mMediaProjection;    private Intent mResultData;    private int mResultCode;    private VirtualDisplay mVirtualDisplay;    private ImageToBitmapAsyncTask mImageToBitmapTask;    public ScreenCaptureFragment() {    }    @Override    public void onActivityCreated(@Nullable Bundle savedInstanceState) {        super.onActivityCreated(savedInstanceState);        mMediaProjectionManager = ((MediaProjectionManager) getActivity().getSystemService(Context.MEDIA_PROJECTION_SERVICE));        setupImageReader();    }    @TargetApi(Build.VERSION_CODES.KITKAT)    private void setupImageReader() {        DisplayMetrics displayMetrics = Resources.getSystem().getDisplayMetrics();        mScreenDensity = displayMetrics.densityDpi;        mScreenWidth = displayMetrics.widthPixels;        mScreenHeight = displayMetrics.heightPixels;//      图片格式PixelFormat.RGBA_8888不是乱写的，与Bitmap.Config的图片格式对应        mImageReader = ImageReader.newInstance(mScreenWidth, mScreenHeight, PixelFormat.RGBA_8888, 1);    }    /**     * 启动截屏     *     * @param onCaptureFinishedListener 截屏完成的监听器     */    public void startCapture(OnCaptureFinishedListener onCaptureFinishedListener) {        mOnCaptureFinishedListener = onCaptureFinishedListener;        if (mMediaProjection != null) {// 如果已经有令牌，直接拓印屏幕内容            setupVirtualDisplay();        } else if (mResultData != null && mResultCode != 0) {// 如果已经获得录屏权限，构建MediaProjection，然后拓印屏幕内容            setupMediaProjection();            setupVirtualDisplay();        } else {// 如果没有录屏权限：请求录屏权限            requestCapturePermission(REQUEST_CAPTURE);        }    }    @Override    public void onActivityResult(int requestCode, int resultCode, Intent data) {        if (requestCode == REQUEST_CAPTURE) {            if (resultCode != RESULT_OK) {                Log.e(TAG, "截屏权限被禁止！");                return;            }            mResultCode = resultCode;            mResultData = data;            setupMediaProjection();            setupVirtualDisplay();        }    }    /*获得MediaProjection:一个允许程序截取屏幕内容的令牌*/    @TargetApi(Build.VERSION_CODES.LOLLIPOP)    private void setupMediaProjection() {        mMediaProjection = mMediaProjectionManager.getMediaProjection(mResultCode, mResultData);    }    @TargetApi(Build.VERSION_CODES.LOLLIPOP)    private void requestCapturePermission(int requestCode) {        startActivityForResult(mMediaProjectionManager.createScreenCaptureIntent(), requestCode);    }    /*获得虚拟显示，可理解为拓印屏幕内容*/    @TargetApi(Build.VERSION_CODES.LOLLIPOP)    private void setupVirtualDisplay() {        if (mImageToBitmapTask != null && mImageToBitmapTask.isRunning()) {            Log.e(TAG,"There is already a task running");            return;        }        Image image;        do {            mVirtualDisplay = mMediaProjection.createVirtualDisplay("ScreenCaptor",                    mScreenWidth, mScreenHeight, mScreenDensity,                    DisplayManager.VIRTUAL_DISPLAY_FLAG_AUTO_MIRROR,                    mImageReader.getSurface(), null, null);            image = mImageReader.acquireNextImage();        } while (image == null);        mImageToBitmapTask = new ImageToBitmapAsyncTask(mOnCaptureFinishedListener);        mImageToBitmapTask.execute(image);    }    private static class ImageToBitmapAsyncTask extends AsyncTask<Image, Void, Bitmap> {        private boolean isRunning;        private WeakReference<OnCaptureFinishedListener> mListenerWeakReference;        public ImageToBitmapAsyncTask(OnCaptureFinishedListener listener) {            mListenerWeakReference = new WeakReference<>(listener);        }        @Override        protected void onPreExecute() {            isRunning = true;        }        @Override        protected Bitmap doInBackground(Image... images) {            Image image = null;            if (images != null && images.length > 0) {                image = images[0];            }            if (image != null) {                return imageToBitmap(images[0]);            }            return null;        }        @TargetApi(Build.VERSION_CODES.KITKAT)        private Bitmap imageToBitmap(Image image) {            if (image == null) {                return null;            }            try {                int width = image.getWidth();                int height = image.getHeight();                final Image.Plane[] planes = image.getPlanes();                final ByteBuffer buffer = planes[0].getBuffer();                //每个像素的间距                int pixelStride = planes[0].getPixelStride();                //总的间距                int rowStride = planes[0].getRowStride();                int rowPadding = rowStride - pixelStride * width;                Bitmap bitmap = Bitmap.createBitmap(width + rowPadding / pixelStride, height, Bitmap.Config.ARGB_8888);                bitmap.copyPixelsFromBuffer(buffer);                return Bitmap.createBitmap(bitmap, 0, 0, width, height);            } catch (ArithmeticException e) {                return null;            } finally {                image.close();            }        }        @Override        protected void onPostExecute(Bitmap bitmap) {            isRunning = false;            OnCaptureFinishedListener listener = mListenerWeakReference.get();            if (listener == null) {                return;            }            if (bitmap != null) {                listener.onCaptureSuccess(bitmap);            } else {                listener.onCaptureFailure();            }        }    @Override        protected void onCancelled() {            isRunning = false;        }        public boolean isRunning() {            return isRunning;        }    }    @Override    public void onPause() {        super.onPause();        stopMediaProjection();    }    @Override    public void onDestroy() {        super.onDestroy();        if (mImageToBitmapTask != null && !mImageToBitmapTask.isRunning()) {            mImageToBitmapTask.cancel(true);            mImageToBitmapTask = null;        }        releaseVirtualDisplay();    }    @TargetApi(Build.VERSION_CODES.LOLLIPOP)    private void stopMediaProjection() {        if (mMediaProjection != null) {            mMediaProjection.stop();            mMediaProjection = null;        }    }    @TargetApi(Build.VERSION_CODES.KITKAT)    private void releaseVirtualDisplay() {        if (mVirtualDisplay == null) {            return;        }        mVirtualDisplay.release();        mVirtualDisplay = null;    }}

使用时不需要再重写onActivityResult方法了：

public class ScreenCaptureActivity extends AppCompatActivity implements ScreenCaptureFragment.OnCaptureFinishedListener {    private ImageView mImageView;    protected ScreenCaptureFragment mCaptureFragment;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_api_shot);        mImageView = findViewById(R.id.image_view);        mCaptureFragment = new ScreenCaptureFragment();        getSupportFragmentManager().beginTransaction().add(mCaptureFragment,"capture").commit();    }    public void onClick(View view) {        switch (view.getId()) {            case R.id.start_capture:                mCaptureFragment.startCapture(this);                break;        }    }    @Override    public void onCaptureSuccess(Bitmap bitmap) {        mImageView.setImageBitmap(bitmap);    }    @Override    public void onCaptureFailure() {    }}

贴上源码地址：https://github.com/sheaye/ScreenCaptureTest