public static void quit(Context context) {
	AlertDialog.Builder alertbBuilder = new AlertDialog.Builder(context);
	alertbBuilder.setTitle("您确定需要退出？")
			.setPositiveButton("确定", new DialogInterface.OnClickListener() {

				@Override
				public void onClick(DialogInterface dialog, int which) {
					// 结束这个Activity

					int nPid = android.os.Process.myPid();

					android.os.Process.killProcess(nPid);
				}
			})
			.setNegativeButton("取消", new DialogInterface.OnClickListener() {

				@Override
				public void onClick(DialogInterface dialog, int which) {
					dialog.cancel();

				}
			}).create();
	alertbBuilder.show();

}

@Override
public boolean onKeyDown(int keyCode, KeyEvent event) {

	if (keyCode == KeyEvent.KEYCODE_BACK && event.getRepeatCount() == 0) {
		Commons.quit(this);
	}
	return true;
}