相机意图捕获的图片文件在onActivityResult中暂时为空

Question

我在尝试通过 intent 拍照时遇到了一个非常奇怪的错误。 Activity 代码（稍微简化）：

private void startCapture() throws IOException {
    // Create output file
    final File photoFile = makePhotoFile();
    _photoPath = photoFile.getAbsolutePath();

    Intent cameraIntent = new Intent(MediaStore.ACTION_IMAGE_CAPTURE);
    /* IMPORTANT NOTE TO READERS
     * As of Android N (which went out shortly after I posted this question),
     * you cannot use Uri.fromFile this way anymore.
     * You should use a FileProvider. */
    cameraIntent.putExtra(MediaStore.EXTRA_OUTPUT, Uri.fromFile(photoFile));

    if (cameraIntent.resolveActivity(getPackageManager()) != null) {
        startActivityForResult(cameraIntent, REQUEST_CODE_IMAGE_CAPTURE);
    }
    else {
        deleteCurrentPhoto();
    }
}

private File makePhotoFile() throws IOException {
    String timeStamp = new SimpleDateFormat("yyyyMMdd_HHmmss", Locale.ENGLISH).format(new Date());
    String imageFileName = "MyPhoto_" + timeStamp + "_";
    File storageDir = getExternalFilesDir(Environment.DIRECTORY_PICTURES);
    return File.createTempFile(imageFileName, ".jpg", storageDir);
}

@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
    super.onActivityResult(requestCode, resultCode, data);

    if(requestCode == REQUEST_CODE_IMAGE_CAPTURE) {
        if(resultCode == RESULT_OK) {
            ByteArrayOutputStream bos = new ByteArrayOutputStream();
            final byte[] buffer = new byte[2048];
            int read;
            byte[] photoBytes;
            try(FileInputStream fis = new FileInputStream(_photoPath)) {

                for(int i=0; i<10; i++) { // Always working after first iteration though
                    if( (read = fis.read(buffer)) <= 0) {
                        // Why does this get printed once ??
                        Log.w("my.package.my.app", "Empty for now...");
                    }
                    else {
                        Log.w("my.package.my.app", "Working now !");
                        bos.write(buffer, 0, read);
                        break;
                    }
                }

                while((read = fis.read(buffer)) >= 0) {
                    bos.write(buffer, 0, read);
                }

                photoBytes = bos.toByteArray();
            } // Catch clauses removed for simplicity

            // Everything working OK after that (photoBytes decodes fine with the BitmapFactory)
        }
    }
}

并且日志输出：

03-01 16:32:34.139 23414-23414/my.package.my.app W/my.package.my.app: Empty for now... 03-01 16:32:34.139 23414-23414/my.package.my.app W/my.package.my.app: Working now !

可以看到，在拍照后的onActivityResult中，第一次调用FileInputStream.read时文件是空的...然后就可以正确读取了！我以为当相机意图 returns 调用 activity 时，文件已经写入。有什么延迟吗？我也很惊讶地看到它总是在 for 循环中恰好一次迭代后工作。

注意，如果我在onActivityResult的开头打断点，会稍微延迟执行，一切正常（第一次尝试正确读取文件）。

我在 Android 6.0.1 下使用普通 Nexus 6P 和普通相机应用程序。

重要编辑：至于 Android N，您应该使用 FileProvider 而不是像我之前那样使用 Uri.fromFile。参见 this blog post and these explanations from the Android team。

Answer 1

尚未创建该文件。删除 File.createTempFile().

您唯一需要的是文件名。文件路径。相机应用程序将自行创建文件。所以改变你的功能来创建新的文件名。例如。 new File(storageDir, imageFileName + ".jpg")

相机意图捕获的图片文件在onActivityResult中暂时为空

Picture file captured with camera intent empty for a while in onActivityResult

android

android-intent

android-camera

android-file

android-camera-intent