How to get scroll percentage in NestedScrollView anytime (smoothly)?

Question

I want to change the alpha of the toolbar base to scroll, as shown below:

First, the toolbar is transparent and, scrolling from the bottom, it becomes more visible, and in the end it will be completely opaque (visible).

The structure of my layout:

<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>

The contents of the nested scrollview will dynamically change from the server, so I don’t know its height.

I just found 2 ways to detect scrollY:

• addOnScrollChangedListener

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

• setOnScrollChangeListener

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

But none of these methods is smooth. for example, if you check the value scrollY(using log.d()), you will see something like:

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

There is a big gap between the numbers.

: ()? ?

Answer 1

scrollListener ScrollView.

scrollView:

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

---

---

• : scrollY = scrollView.getScrollY()

• ScrollView scrollContentHeight = scrollView.getChildAt(0).getHeight() - scrollView.

• : scrollContentHeight - screenHeight + statusBarHeight

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

• : 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));
        }
    });

Answer 2

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);
            }
        });

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