AsyncTask：不将数据写入文件

Question

我是 Android 编程的新手，我一直在提供一些代码来解决一个我似乎有一段时间无法弄清楚的问题。

我有一个 AsyncTask 正在尝试将一些数据保存到放置在设备内部存储上的文件中。该文件已创建，但填充了 0 个字节

public void exportFile(final Context mContext, boolean debug) {

    try {
        final String path = Environment.getExternalStorageDirectory()
                .getAbsolutePath() + "/DroidP";
        File dir = new File(path);
        dir.mkdirs();

        final File file = new File(dir, "Droid_export.txt");

        if (file.exists()) {
            file.delete();                          
        }

        file.createNewFile();

        final FileWriter out = new FileWriter(file,true);



        final int totalLines = recordsIdList.size();
        new AsyncTask<Void, String, Void>() {
            ProgressDialog progressDialog;

            @Override
            protected Void doInBackground(Void... arg0) {
                try {



                    List<byte[]> mainBuffer = new ArrayList<byte[]>();

                    int i = 0;
                    int size = 0;

                    for (Integer r : recordsIdList) {
                        Log.i("test", db.getRecord(r).toExportSQL());

                        byte[] buffer = db.getRecord(r).toExportSQL().getBytes(); 
                        mainBuffer.add(buffer);
                        size += buffer.length;

                        publishProgress("Writing " + (i++) + " from "+ totalLines);
                    }

                    int pos = 0;
                    char[] outBuffer = new char[size];
                    for(byte[] chunk : mainBuffer) {
                        for(i=0;i<chunk.length;i++) {
                            outBuffer[pos] = (char)chunk[i];
                            pos++;
                        }                           
                    }

                    out.write(outBuffer);

                    out.flush();



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

            @Override
            protected void onProgressUpdate(String... progress) {
                progressDialog.setMessage(progress[0]);
            }

            @Override
            protected void onPostExecute(Void result) {
                super.onPostExecute(result);
                try {
                    out.close();
                } catch (IOException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }

                progressDialog.dismiss();
            }

            @Override
            protected void onPreExecute() {
                progressDialog = ProgressDialog.show(mContext,
                        "Exporting file", "", true);
            }
        }.execute((Void) null);
        Intent intent = new Intent(Intent.ACTION_MEDIA_SCANNER_SCAN_FILE);
        intent.setData(Uri.fromFile(file.getAbsoluteFile()));
        sendBroadcast(intent);
    } catch (Exception e) {

    }
}

当我查看日志时，我可以看到我试图保存到文件中的数据，这是正确的，但是一旦 AsyncTask 完成，文件就会创建为 0 字节。我是遗漏了什么？请记住，我对 Android 编程还很陌生。

Answer 1

我尚未测试您的错误，但您可以通过跳过 byte 到 char 的转换并将文件处理移动到 async 任务中来简化您的问题，正如许多人所建议的那样。

试试这样的：

private Boolean isExporting = false;

public void exportFile(final Context mContext, boolean debug) {
    if (!isExporting) {
        isExporting = true;
        new AsyncTask<Void, String, Void>() {
            ProgressDialog progressDialog;

            @Override
            protected Void doInBackground(Void... arg0) {
                try {
                    // read data into byte array
                    final ByteArrayOutputStream baos = new ByteArrayOutputStream();
                    int i = 0;
                    for (Integer r : recordsIdList) {
                        byte[] buffer = db.getRecord(r).toExportSQL().getBytes();
                        Log.i("test", new String(buffer));
                        baos.write(buffer);
                        publishProgress("Writing " + (i++) + " from " + totalLines);
                    }
                    baos.close();
                    // write data to file
                    final String path = Environment.getExternalStorageDirectory().getAbsolutePath() + "/DroidP";
                    final File dir = new File(path);
                    dir.mkdirs();
                    final File file = new File(dir, "Droid_export.txt");
                    file.createNewFile();
                    final FileOutputStream fos = new FileOutputStream(file);
                    fos.write(baos.toByteArray());
                    fos.close();
                } catch (Exception e) {
                    e.printStackTrace();
                }
                return null;
            }

            @Override
            protected void onProgressUpdate(String... progress) {
                progressDialog.setMessage(progress[0]);
            }

            @Override
            protected void onPostExecute(Void result) {
                super.onPostExecute(result);
                isExporting = false;
                progressDialog.dismiss();
            }

            @Override
            protected void onPreExecute() {
                progressDialog = ProgressDialog.show(mContext,
                        "Exporting file", "", true);
            }
        }.execute();
    }
}