Android - 使用确定的 ProgressDialog 将位图保存到 SD 卡

Question

我正在使用此 AsyncTask 将我的图像资源保存到 SD 卡：

public class SaveImageAsync extends AsyncTask<String, String, String> {

    private Context mContext;

    int imageResourceID;

    private ProgressDialog mProgressDialog;

    public SaveImageAsync(Context context, int image) 
    {
        mContext = context;
        imageResourceID = image;
    }

    @Override
    protected void onPreExecute() {
        super.onPreExecute();
        mProgressDialog = new ProgressDialog(mContext);
        mProgressDialog.setMessage("Saving Image to SD Card");
        mProgressDialog.setMax(100);
        mProgressDialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);
        mProgressDialog.setIndeterminate(true);
        mProgressDialog.setCancelable(false);
        mProgressDialog.show();
    }

    @SuppressLint("NewApi")
    @Override
    protected String doInBackground(String... filePath) {
        try {


            Bitmap bitmap = BitmapFactory.decodeResource(mContext.getResources(), imageResourceID);

            ByteArrayOutputStream bos = new ByteArrayOutputStream(); 
            bitmap.compress(CompressFormat.JPEG, 100, bos); 
            byte[] bitmapdata = bos.toByteArray();
            ByteArrayInputStream bis = new ByteArrayInputStream(bitmapdata);

            int lenghtOfFile = bitmap.getByteCount();
            Log.d("LOG", "File Lenght = " + lenghtOfFile);

            byte[] buffer = new byte[64];
            int len1 = 0;
            long total = 0;

            while ((len1 = bis.read(buffer)) > 0) {
                total += len1;
                publishProgress("" + (int) ((total * 100) / lenghtOfFile));
                bos.write(buffer, 0, len1);
            }
            bos.flush();
            bos.close();
            bitmap.recycle();
            bis.close();

            return getTempUri().getPath();
        } catch (Exception e) {
            return null;
        }


    }

    protected void onProgressUpdate(String... progress) {
        mProgressDialog.setIndeterminate(false);
        mProgressDialog.setProgress(Integer.parseInt(progress[0]));
    }

    @Override
    protected void onPostExecute(String filename) {
        // dismiss the dialog after the file was saved
        try {
            mProgressDialog.dismiss();
            mProgressDialog = null;
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    private Uri getTempUri() {
        return Uri.fromFile(getTempFile());
    }

    private File getTempFile() {
        if (Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)) {

            File directory = new File(mContext.getExternalCacheDir().getPath());
            directory.mkdirs();
            File file = new File(directory , "temp.jpg");
            try  {
                file.createNewFile();
            }  catch (IOException e) {}
            return file;
        } else  {
            return null;
        }
    }   
}

我从我的活动中调用它：

new SaveImageAsync(this, R.drawable.my_image_resource).execute();

它工作正常，问题是bitmap.getByteCount();返回的位图大小与保存文件的最终大小完全不同。过程完成时的结果，指示的进度仅多或少 20%。

有什么方法可以在保存之前知道文件的最终大小？谢谢。

Answer 1

您使用 PNG 压缩，这种压缩效果的好坏取决于图像的实际内容，即仅包含空白的空白图像尺寸较小，所有像素不同的彩色图像尺寸较大。这么长的故事...bitmap.getByteCount() 为您提供了将多少字节用于将实际图像存储在内存中（未压缩）而不是 SD 卡（压缩）的信息。您的期望与实际所得之间的差异解释了约 20% 的转折点。

如果我猜想一个解决方案可能是使用位图数据数组的长度。我修改了你的代码：

Bitmap bitmap = null;

ByteArrayOutputStream bos = new ByteArrayOutputStream(); 
bitmap.compress(CompressFormat.JPEG, 100, bos); 
byte[] bitmapdata = bos.toByteArray();
ByteArrayInputStream bis = new ByteArrayInputStream(bitmapdata);

int lenghtOfFile = bitmapdata.length;
byte[] buffer = new byte[64];
int currentProcess = 0;
int totalReadedYet = 0;

try {
while ((currentProcess = bis.read(buffer)) > 0) {
    totalReadedYet += currentProcess;
    publishProgress(Integer.toString((int) ((totalReadedYet) / lenghtOfFile)));
    bos.write(buffer, 0, currentProcess);
}

bos.flush();
bos.close();
bitmap.recycle();
bis.close();
} catch (IOException e) {
    e.printStackTrace();
}

Answer 2

感谢 Baschi 的回答，bitmapdata.length; 正是我所需要的，这是我的AsyncTask 用于将bitmap 与Determinated ProgressBar 保存到 SD 卡中，我希望有人会觉得它有用：

public class SaveImageAsync extends AsyncTask<Void, String, Void> {

    private Context mContext;
    private int imageResourceID;

    private ProgressDialog mProgressDialog;

    public SaveImageAsync(Context context, int image) {
        mContext = context;
        imageResourceID = image;
    }

    @Override
    protected void onPreExecute() {
        super.onPreExecute();
        mProgressDialog = new ProgressDialog(mContext);
        mProgressDialog.setMessage("Saving Image to SD Card");
        mProgressDialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);
        mProgressDialog.setIndeterminate(true);
        mProgressDialog.setCancelable(false);
        mProgressDialog.show();
    }

    @Override
    protected Void doInBackground(Void... filePath) {
        try {
            Bitmap bitmap = BitmapFactory.decodeResource(mContext.getResources(), imageResourceID);

            ByteArrayOutputStream byteOutputStream = new ByteArrayOutputStream(); 
            bitmap.compress(CompressFormat.JPEG, 100, byteOutputStream); 
            byte[] mbitmapdata = byteOutputStream.toByteArray();
            ByteArrayInputStream inputStream = new ByteArrayInputStream(mbitmapdata);

            String baseDir = Environment.getExternalStorageDirectory().getAbsolutePath();
            String fileName = "mySavedImage.jpg";

            OutputStream outputStream = new FileOutputStream(baseDir + File.separator + fileName);
            byteOutputStream.writeTo(outputStream);

            byte[] buffer = new byte[128]; //Use 1024 for better performance
            int lenghtOfFile = mbitmapdata.length;
            int totalWritten = 0;
            int bufferedBytes = 0;

            while ((bufferedBytes = inputStream.read(buffer)) > 0) {
                totalWritten += bufferedBytes;
                publishProgress(Integer.toString((int) ((totalWritten * 100) / lenghtOfFile)));
                outputStream.write(buffer, 0, bufferedBytes);
            }

        } catch (IOException e) { e.printStackTrace(); }
        return null;

    }

    protected void onProgressUpdate(String... progress) {
        mProgressDialog.setIndeterminate(false);
        mProgressDialog.setProgress(Integer.parseInt(progress[0]));
    }

    @Override
    protected void onPostExecute(Void filename) {
        mProgressDialog.dismiss();
        mProgressDialog = null;
    }
}

在您的Activity 中使用这一行来保存图像：

new SaveImageAsync(this, R.drawable.your_image_resource).execute();