在Android 6.0以上的系统中,要获取外部存储器(也就是SD卡)的数据,需要先动态申请SD卡读写权限。具体思路如下:
1.在项目的AndroidManifest.xml文件中添加如下权限:
private void requestPermission(String permission) { if (ContextCompat.checkSelfPermission(this, permission) != PackageManager.PERMISSION_GRANTED) { ActivityCompat.requestPermissions(this, new String[]{permission}, 1); } }
@Override public void onRequestPermissionsResult(int requestCode, String[] permissions, int[] grantResults) { if (requestCode == 1) { if (grantResults[0] == PackageManager.PERMISSION_GRANTED) { //用户授权了,进行文件读取操作 readFileFromExternalStorage(); } else { Toast.makeText(this, "没有授权读取SD卡", Toast.LENGTH_SHORT).show(); } } }
4.读取文件。拥有授权后,就可以通过File类的相关API读取外部存储器的数据了。如下面的示例代码所示,该代码可以读取SD卡根目录下的hello.txt文件。
private void readFileFromExternalStorage() { String state = Environment.getExternalStorageState(); if (Environment.MEDIA_MOUNTED.equals(state)) { File sdCardDir = Environment.getExternalStorageDirectory(); File file = new File(sdCardDir, "hello.txt"); try { FileInputStream fis = new FileInputStream(file); BufferedReader br = new BufferedReader(new InputStreamReader(fis)); StringBuilder sb = new StringBuilder(); String line; while ((line = br.readLine()) != null) { sb.append(line); } br.close(); fis.close(); Toast.makeText(this, sb.toString(), Toast.LENGTH_SHORT).show(); } catch (IOException e) { e.printStackTrace(); } } else { Toast.makeText(this, "SD卡未挂载", Toast.LENGTH_SHORT).show(); } }