如何在NestedScrollView中随时(平滑地)获得滚动百分比？

Question

我想在滚动时更改工具栏的alpha,如下所示:

首先,工具栏是透明的,通过滚动到底部,它将越来越可见,最后它将是完全不透明(可见).

我的布局结构是:

<android.support.design.widget.CoordinatorLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:layout_width="match_parent"
android:layout_height="match_parent">

    <android.support.design.widget.AppBarLayout
    android:id="@+id/app_bar_layout"
    android:layout_width="match_parent"
    android:layout_height="wrap_content">

    <android.support.design.widget.CollapsingToolbarLayout
        android:id="@+id/collapsing_toolbar"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        app:contentScrim="?attr/colorPrimary"
        app:layout_scrollFlags="scroll|exitUntilCollapsed">

        <RelativeLayout
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            app:layout_collapseMode="parallax">

            ....

        </RelativeLayout>

    </android.support.design.widget.CollapsingToolbarLayout>

    </android.support.design.widget.AppBarLayout>

    <android.support.v4.widget.NestedScrollView
    android:id="@+id/scroll"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:clipToPadding="false"
    app:layout_behavior="@string/appbar_scrolling_view_behavior">

         ....

    </android.support.v4.widget.NestedScrollView>

</android.support.design.widget.CoordinatorLayout>

嵌套的scrollview的内容将从服务器动态更改,所以我不知道它的高度.

我刚刚发现了两种检测scrollY的方法:

1. addOnScrollChangedListener:

   scroll.getViewTreeObserver().addOnScrollChangedListener(new ViewTreeObserver.OnScrollChangedListener() {
    @Override
    public void onScrollChanged() {
       // use scroll.getScrollY()     
   }
   });
   

2. setOnScrollChangeListener:

   scroller.setOnScrollChangeListener(new NestedScrollView.OnScrollChangeListener() {
   
   @Override
   public void onScrollChange(NestedScrollView v, int scrollX, int scrollY, int oldScrollX, int oldScrollY) {
   
   }
   });
   

但这些方式都不顺利.例如,如果您检查scrollY(通过使用log.d())的值,您将看到如下内容:

scrollY: 58
scrollY: 117
scrollY: 167
scrollY: 192
scrollY: 195
scrollY: 238
scrollY: 281
scrollY: 338 

数字之间存在很大差距.

我的问题是:如何获得每时每刻的滚动百分比(顺利)？或者根据滚动的当前位置改变工具栏的alpha的任何其他方式？

Answer 1

尝试这个

scrollview.getViewTreeObserver().addOnScrollChangedListener(new ViewTreeObserver.OnScrollChangedListener() {
            @Override
            public void onScrollChanged() {
                double scrollViewHeight = scrollview.getChildAt(0).getBottom() - scrollview.getHeight();
                double getScrollY = scrollview.getScrollY();
                double scrollPosition = (getScrollY / scrollViewHeight) * 100d;
                Log.i("scrollview", "scroll Percent Y: " + (int) scrollPosition);
            }
        });

它将显示从 0 到 100% 的百分比

Answer 2

您可以添加scrollListener ScrollView.

滚动视图的滚动百分比的计算:

double percent = ((((float) scrollY) / ((float) (scrollContentHeight - screenHeight + statusBarHeight))));

• 视图显示部分的上边缘: scrollY = scrollView.getScrollY()

• 该scrollView有一个孩子,scrollContentHeight = scrollView.getChildAt(0).getHeight()是滚动型的内容的高度.

• 我们需要计算完全滚动状态下顶边的最大高度: scrollContentHeight - screenHeight + statusBarHeight

• 完了! percent = scrollY*100 / (scrollContentHeight - screenHeight + statusBarHeight)

• 并设置颜色: view.setBackgroundColor(Color.argb((int) (255.0 * (percent/100)), r, g, b));

scrollView.getViewTreeObserver().addOnScrollChangedListener(new ViewTreeObserver.OnScrollChangedListener() {
        @Override
        public void onScrollChanged() {
            int scrollY = scrollView.getScrollY();
            int scrollContentHeight = scrollView.getChildAt(0).getHeight();
            int screenHeight = Utility.getScreenHeight(context);
            int statusBarHeight = Utility.getStatusBarHeight(context);

            int color = getResources().getColor(R.color.colorPrimary);
            int r = (color >> 16) & 0xFF;
            int g = (color >> 8) & 0xFF;
            int b = (color >> 0) & 0xFF;

            double percent = ((((float) scrollY) / ((float) (scrollContentHeight - screenHeight + statusBarHeight))));
            if (percent >= 0 && percent <= 1)
                toolbar.setBackgroundColor(Color.argb((int) (255.0 * percent), r, g, b));
        }
    });