android 讀寫SD卡上的文件

首先增加權限

主要的activity

public class MainActivity extends Activity {

private EditText et1;
private EditText et2;
private Button bt1;
private Button bt2;
final String FILE_NAME = "crazyit.bin";

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
et1 = (EditText) findViewById(R.id.editText1);
et2 = (EditText) findViewById(R.id.editText2);
bt1 = (Button) findViewById(R.id.button1);
bt2 = (Button) findViewById(R.id.button2);
bt1.setOnClickListener(new OnClickListener() {

@Override
public void onClick(View arg0) {
write(et1.getText().toString());
et1.setText("");
}
});
bt2.setOnClickListener(new OnClickListener() {

@Override
public void onClick(View v) {
et2.setText(read());
}
});

}

private String read() {

try {
if (Environment.getExternalStorageState().equals(
Environment.MEDIA_MOUNTED)) {
File sdcardDir = Environment.getExternalStorageDirectory();
FileInputStream fis = openFileInput(sdcardDir
.getCanonicalPath() + FILE_NAME);
BufferedReader br = new BufferedReader(new InputStreamReader(
fis));
StringBuilder sb = new StringBuilder();
String line = null;
while ((line = br.readLine()) != null) {
sb.append(line);
}
br.close();
return sb.toString();
}
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
return null;
}

private void write(String content) {
try {
if (Environment.getExternalStorageState().equals(
Environment.MEDIA_MOUNTED)) {
File sdcardDir = Environment.getExternalStorageDirectory();
File targetFile = new File(sdcardDir.getAbsoluteFile()
.getCanonicalPath() + FILE_NAME);
RandomAccessFile raf = new RandomAccessFile(targetFile, "rw");
raf.seek(targetFile.length());
raf.write(content.getBytes());
raf.close();
}
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}

}