android的退出对话框

   @Override
public boolean onKeyDown(int keyCode, KeyEvent event) {
// TODO Auto-generated method stub


if (keyCode == KeyEvent.KEYCODE_BACK) {


AlertDialog.Builder builder = new AlertDialog.Builder(getParent());
builder.setMessage("你确定退出吗？")
.setCancelable(false)
.setPositiveButton("确定",
new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog,
int id) {
finish();
System.exit(0);
}
})
.setNegativeButton("返回",
new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog,
int id) {
dialog.cancel();
}
});
AlertDialog alert = builder.create();
alert.show();
return true;
}


return super.onKeyDown(keyCode, event);
}