Image image = imageReader.acquireNextImage();
截屏时这句话报空指针（为什么我总和空指针杠上），原因是：读取截屏数据，对象的创建完成需要一定的时间，从创建对象到图片数据真正可用需要在OnImageAvailableListener的回调方法中完成

mImageReader.setOnImageAvailableListener(new ImageReader.OnImageAvailableListener() {
            @Override
            public void onImageAvailable(ImageReader mImageReader) {

                Image image = null;
                try {
                    image = mImageReader.acquireLatestImage();
                    if (image != null) {
                        final Image.Plane[] planes = image.getPlanes();
                        if (planes.length > 0) {
                            final ByteBuffer buffer = planes[0].getBuffer();
                            int pixelStride = planes[0].getPixelStride();
                            int rowStride = planes[0].getRowStride();
                            int rowPadding = rowStride - pixelStride * mWidth;


                            // create bitmap
                            Bitmap bmp = Bitmap.createBitmap(mWidth + rowPadding / pixelStride,
                                    mHeight, Bitmap.Config.ARGB_8888);
                            bmp.copyPixelsFromBuffer(buffer);

                            Bitmap croppedBitmap = Bitmap.createBitmap(bmp, 0, 0, mWidth, mHeight);

                            saveBitmap(croppedBitmap);//保存图片

                            if (croppedBitmap != null) {
                                croppedBitmap.recycle();
                            }
                            if (bmp != null) {
                                bmp.recycle();
                            }
                        }
                    }

                } catch (Exception e) {
                    e.printStackTrace();
                } finally {
                    if (image != null) {
                        image.close();
                    }
                    if (mImageReader != null) {
                        mImageReader.close();
                    }
                    if (display != null) {
                        display.release();
                    }

                    mImageReader.setOnImageAvailableListener(null, null);
                    mProjection.stop();

                    onScreenshotTaskOver();
                }

            }
        }, getBackgroundHandler());

是的好多地方都没有给出 getBackgroundHandler 这个 handler 的使用方式，于是在参考网址【1】中扒了作者的源代码下来：

//在后台线程里保存文件
    Handler backgroundHandler;

    private Handler getBackgroundHandler() {
        if (backgroundHandler == null) {
            HandlerThread backgroundThread =
                    new HandlerThread("catwindow", android.os.Process
                            .THREAD_PRIORITY_BACKGROUND);
            backgroundThread.start();
            backgroundHandler = new Handler(backgroundThread.getLooper());
        }
        return backgroundHandler;
    }

格式什么的以后再说咯

参考：1、http://www.tk4479.net/SpringIOC/article/details/78568438
2、https://github.com/miqt/CapWindow