// 向SD卡写入数据     private void writeSDcard(String str) {         try {             // 推断是否存在SD卡             if (Environment.getExternalStorageState().equals(                     Environment.MEDIA_MOUNTED)) {                 // 获取SD卡的文件夹                 File sdDire = Environment.getExternalStorageDirectory();                 FileOutputStream outFileStream = new FileOutputStream(                         sdDire.getCanonicalPath() + "/test.txt");                 outFileStream.write(str.getBytes());                 outFileStream.close();                 Toast.makeText(this, "数据保存到text.txt文件了", Toast.LENGTH_LONG)                         .show();             }         } catch (Exception e) {             e.printStackTrace();         }     }           // 从SD卡中读取数据     private void readSDcard() {         StringBuffer strsBuffer = new StringBuffer();         try {             // 推断是否存在SD             if (Environment.getExternalStorageState().equals(                     Environment.MEDIA_MOUNTED)) {                 File file = new File(Environment.getExternalStorageDirectory()                         .getCanonicalPath() + "/test.txt");                 // 推断是否存在该文件                 if (file.exists()) {                     // 打开文件输入流                     FileInputStream fileR = new FileInputStream(file);                     BufferedReader reads = new BufferedReader(                             new InputStreamReader(fileR));                     String st = null;                     while ((st = reads.readLine()) != null) {                         strsBuffer.append(st);                     }                     fileR.close();                 } else {                     Toast.makeText(this, "该文件夹下文件不存在", Toast.LENGTH_LONG).show();                 }             }         } catch (Exception e) {             e.printStackTrace();         }         Toast.makeText(this, "读取到的数据是：" + strsBuffer.toString() + "",                 Toast.LENGTH_LONG).show();     } }