Android SD卡写入,权限被拒绝

Question

我正在尝试使用以下代码将文件写入SDCard(android.permission.WRITE_EXTERNAL_STORAGE已在manifest.xml中设置权限).执行nmea_file.createNewFile();它时抛出异常Permission Denied.

任何猜测为什么会发生这种情况？

if(!Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)) 
  {
     Log.d(TAG, "Sdcard was not mounted !!" ); 
  }
else
  {
    File nmea_file; 
    File root = Environment.getExternalStorageDirectory();
    FileWriter nmea_writer = null;
    try {
        nmea_file = new File(root,"NMEA.txt");
        if(!nmea_file.exists()) {
                Log.w(TAG, "File Doesn't Exists!");
                nmea_file.createNewFile();
            }
        nmea_writer = new FileWriter(nmea_file);
        nmea_writer.append(nmea);
        nmea_writer.flush();
    }
    catch (IOException e) 
    {
        Log.w(TAG, "Unable to write", e);
    } 
    finally 
    {
        if (nmea_writer != null) 
        {
            try 
            {
                nmea_writer.close();
            } 
            catch (IOException e) 
            {
                Log.w(TAG, "Exception closing file", e);
            }
        }
    }
  }

Answer 1

添加到manifest.xml

<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />

Answer 2

如果某些操作阻止了SD卡,可能会发生这种情况,例如:

1. 准备从插槽中卸载SD卡
2. 设备连接到PC作为外部USB驱动器

Answer 3

您可能想要检查您是否可以访问SDCARD.以下是如何在代码中执行此操作:

if(!Environment.MEDIA_MOUNTED.equals(Environment.getExternalStorageState())){
    Toast.makeText(this, "External SD card not mounted", Toast.LENGTH_LONG).show();
}