检查盘volumn是否可以写入
通过创建一个临时文件来确定是否盘可写。注意不要把文件放在根目录，因为根目录会现在文件的数目
private static boolean checkFsWritable() { // Create a temporary file to see whether a volume is really writeable. // It's important not to put it in the root directory which may have a // limit on the number of files. String directoryName = Environment.getExternalStorageDirectory().toString() + "/DCIM"; File directory = new File(directoryName); if (!directory.isDirectory()) { if (!directory.mkdirs()) { return false; } } File f = new File(directoryName, ".probe"); try { // Remove stale file if any if (f.exists()) { f.delete(); } if (!f.createNewFile()) { return false; } f.delete(); return true; } catch (IOException ex) { return false; } }