Android开发中如何将滑动组件固定在顶部

public class MainActivity extends AppCompatActivity implements ObservableScrollView.ScrollViewListener {  private ObservableScrollView scrollView;  private Button topBtn1, topBtn2, middleBtn1, middleBtn2;  private View topPanel, middlePanel;  private int topHeight;   @Override  protected void onCreate(Bundle savedInstanceState) {   super.onCreate(savedInstanceState);   setContentView(R.layout.activity_main);   initViews();   initListeners();   }   @Override  public void onWindowFocusChanged(boolean hasFocus) {   super.onWindowFocusChanged(hasFocus);    Rect frame = new Rect();   getWindow().getDecorView().getWindowVisibleDisplayFrame(frame);   int statusBarHeight = frame.top;//状态栏高度    int titleBarHeight = getWindow().findViewById(Window.ID_ANDROID_CONTENT).getTop();//标题栏高度   topHeight = titleBarHeight + statusBarHeight;  }    private void initViews() {   scrollView = (ObservableScrollView) findViewById(R.id.scrollView);   topPanel = findViewById(R.id.topPanel);   topBtn1 = (Button) topPanel.findViewById(R.id.button1);   topBtn2 = (Button) topPanel.findViewById(R.id.button2);    middlePanel = findViewById(R.id.middlePanel);   middleBtn1 = (Button) middlePanel.findViewById(R.id.button1);   middleBtn2 = (Button) middlePanel.findViewById(R.id.button2);   }   private void initListeners() {   topBtn1.setOnClickListener(new View.OnClickListener() {    @Override    public void onClick(View view) {     middleBtn1.setBackgroundColor(Color.WHITE);     topBtn1.setBackgroundColor(Color.WHITE);    }   });    middleBtn1.setOnClickListener(new View.OnClickListener() {    @Override    public void onClick(View view) {     middleBtn1.setBackgroundColor(Color.BLUE);     topBtn1.setBackgroundColor(Color.BLUE);    }   });    scrollView.setScrollViewListener(this);    }    @Override  public void onScrollChanged(ObservableScrollView scrollView, int x, int y, int oldx, int oldy) {   int[] location = new int[2];   middleBtn1.getLocationOnScreen(location);   int locationY = location[1];   Log.e("locationY", locationY + " " + "topHeight的值是：" + topHeight);    if (locationY <= topHeight && (topPanel.getVisibility() == View.GONE || topPanel.getVisibility() == View.INVISIBLE)) {    topPanel.setVisibility(View.VISIBLE);   }    if (locationY > topHeight && topPanel.getVisibility() == View.VISIBLE) {    topPanel.setVisibility(View.GONE);   }   } }