Android 监听返回键|您确定要退出吗

@Override
	public boolean onKeyDown(int keyCode, KeyEvent event) {
		// TODO Auto-generated method stub
		switch (keyCode) {
		case KeyEvent.KEYCODE_BACK:
			AlertDialog.Builder build=new AlertDialog.Builder(this);
			build.setTitle("注意")
					.setMessage("确定要退出吗？")
					.setPositiveButton("确定", new DialogInterface.OnClickListener() {
						
						@Override
						public void onClick(DialogInterface dialog, int which) {
							// TODO Auto-generated method stub
							finish();
							
						}
					})
					.setNegativeButton("取消", new DialogInterface.OnClickListener() {
						
						@Override
						public void onClick(DialogInterface dialog, int which) {
							// TODO Auto-generated method stub
							
						}
					})
					.show();
			break;

		default:
			break;
		}
		return false;
		//return super.onKeyDown(keyCode, event);
		
	}