Android笔记之AsyncTask

AsyncTask中的4个回调

onPreExecute()，在doInBackground(Params...)之前运行在UI线程中

onPostExecute(Result)，在doInBackground(Params...)之后运行在UI线程中

onProgressUpdate(Progress...)，在publishProgress(Progress...)被调用后运行在UI线程中

doInBackground(Params...)，运行在子线程中，这个函数可以调用publishProgress以发布更新到UI线程

示例如下

    public class Md5AsyncTask extends AsyncTask<String, Long, String> {
        @Override
        protected void onPreExecute() {
            super.onPreExecute();
            Log.d(TAG, "onPreExecute() called");
            tv1.setText("已执行");
        }
 
        @Override
        protected void onPostExecute(String s) {
            super.onPostExecute(s);
            Log.d(TAG, "onPostExecute(String) called");
            tv3.setText("已结束");
            tvResult.setText(s);
        }
 
        @Override
        protected void onProgressUpdate(Long... values) {
            super.onProgressUpdate(values);
            tv2.setText(values[0] + "%");
        }
 
        @Override
        protected String doInBackground(String... strings) {
            File file = new File(strings[0]);
            long fileSize = file.length();
            try (BufferedInputStream bis = new BufferedInputStream(new FileInputStream(file))) {
                MessageDigest md5 = MessageDigest.getInstance("MD5");
                byte[] buffer = new byte[10 * 1024 * 1024];
                int numberOfBytesRead;
                long totalNumberOfBytesRead = 0;
                while ((numberOfBytesRead = bis.read(buffer)) != -1) {
                    md5.update(buffer, 0, numberOfBytesRead);
                    totalNumberOfBytesRead += numberOfBytesRead;
                    publishProgress(totalNumberOfBytesRead * 100 / fileSize);
                }
                StringBuilder result = new StringBuilder();
                byte[] digested = md5.digest();
                for (byte e : digested) {
                    String hexStr = Integer.toHexString(e & 255);
                    if (hexStr.length() == 1)
                        result.append('0');
                    result.append(hexStr);
                }
                return result.toString();
            } catch (IOException | NoSuchAlgorithmException ex) {
                Log.e(TAG, null, ex);
                return null;
            }
        }
    }

new Md5AsyncTask().execute(filename);