android读取sdcard路径下的文件的方法

// 读取sdcard文件
private void sdcardread(){
string filename = "/sdcard/my_sdcard.txt";// assets下文件
//string filename = "/sdcard/test/my_sdcard_test.txt";// sdcard下子目录文件
string ret = "";
try {
fileinputstream fis = new fileinputstream(filename);
int len = fis.available();
byte []buffer = new byte[len];

fis.read(buffer);
ret = encodingutils.getstring(buffer, "utf-8");
fis.close();
} catch (exception e) {
e.printstacktrace();
}
tvtxt.settext(ret);
}