Question

我想在布局的底部添加一个按钮。当我向上滚动时，在列表视图中向下，我希望按钮消失，反之亦然。就像在twitter应用程序中一样。在主页的底部有一个textView用于快速推文，当向上滚动时，视图变得不可见。这样做最简单的代码是什么？

Answer 1

您可以使用http://developer.android.com/reference/android/widget/AbsListView.OnScrollListener.html

并在每次滚动时检查listView.getChildAt(0).getTop()位置。如果最后一个顶部位置和当前顶部位置之间的差异为正，则向上滚动。之后，您可以设置按钮的可见性VISIBLE / INVISIBLE

Answer 2

试试这个，创建自定义滚动类，

public class CustomScrollView extends ScrollView {

    private OnArrowChangeListener onArrowChangeListener = null;
    private int id = 0;

    public CustomScrollView(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
        // TODO Auto-generated constructor stub
        id = getId();
    }

    public CustomScrollView(Context context, AttributeSet attrs) {
        super(context, attrs);
        // TODO Auto-generated constructor stub
        id = getId();
    }

    public CustomScrollView(Context context) {
        super(context);
        // TODO Auto-generated constructor stub
        id = getId();
    }

    @Override
    protected void onScrollChanged(int l, int t, int oldl, int oldt) {
        // TODO Auto-generated method stub

        if (getChildCount() == 0) {
            // no child
        } else {
            View view = (View) getChildAt(getChildCount() - 1);
            if (view == null) {
                super.onScrollChanged(l, t, oldl, oldt);
                return;
            }
            int diff = (view.getBottom() - (getHeight() + getScrollY() + view.getTop()));
            // Utility.log(VIEW_LOG_TAG, "@" + diff);
            if (diff <= 10) {
                // bottom reached
                if (onArrowChangeListener != null) {
                    onArrowChangeListener.onReachedBottom(id);
                }
            } else if (t <= 10) {
                // top reached
                if (onArrowChangeListener != null) {
                    onArrowChangeListener.onReachedTop(id);
                }
            } else {
                // middle
                if (onArrowChangeListener != null) {
                    onArrowChangeListener.onVisibleBoth(id);
                }
            }
        }

        super.onScrollChanged(l, t, oldl, oldt);
        // Utility.log(VIEW_LOG_TAG, "v ->" + t);
    }

    public OnArrowChangeListener getOnArrowChangeListener() {
        return onArrowChangeListener;
    }

    public void setOnArrowChangeListener(OnArrowChangeListener onArrowChangeListener) {
        this.onArrowChangeListener = onArrowChangeListener;
    }

    public void computeInitialScroll() {
        CustomScrollView.this.post(new Runnable() {
            @Override
            public void run() {
                if (CustomScrollView.this.getChildCount() > 0) {
                    View view = CustomScrollView.this.getChildAt(0);
                    if (view != null) {
                        int amount = CustomScrollView.this.getMaxScrollAmount();
                        int height = view.getBottom() - view.getTop();
                        if (height < amount || getHeight() > height) {
                            if (onArrowChangeListener != null) {
                                onArrowChangeListener.onInVisibleBoth(id);
                            }
                        }
                    }
                }
            }
        });
    }
}

把它放在你的XMl

中

 <com.app.ui.CustomScrollView
                android:id="@+id/scrollView"
                android:layout_width="match_parent"
                android:layout_height="match_parent"
                android:fillViewport="true"
                android:paddingTop="10dp" >

在您的活动或片段上实现OnScrollListener，

private int pos = 0; listview.setSelection（POS）;

@Override
    public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) {
        // TODO Auto-generated method stub
        pos = firstVisibleItem;
        int first = firstVisibleItem;
        int last = firstVisibleItem + visibleItemCount;

        int adapterSize = totalItemCount;
        if (visibleItemCount >= adapterSize) {
            // Scroll center of items
            return;
        }

        if (first > 0 && last < adapterSize) {
            // middle
            // both visible
            btnUp.setVisibility(View.VISIBLE);
            btnDown.setVisibility(View.VISIBLE);
            return;
        }

        if (last == adapterSize) {
            //Scroll to bottom

            return;
        }

        if (first == 0) {
            //Scroll to top
            return;
        }

    }

    @Override
    public void onScrollStateChanged(AbsListView view, int scrollState) {
        // TODO Auto-generated method stub
    }

如何添加一个在向上滚动时向下消失的视图（在列表视图中向下）并在向下滚动时显示？

2 个答案: