Fustigador Fustigador - 1 month ago 22
Android Question

Detect end of ScrollView

I have an app, that has an Activity that uses a

ScrollView
. I need to detect when user gets to the bottom of the
ScrollView
. I did some googleing and I found this page where is explained. But, in the example, that guys extends
ScrollView
. As I said, I need to extend Activity.

So, I said "ok, let's try to make a custom class extending
ScrollView
, override the
onScrollChanged()
method, detect the end of the scroll, and act accordingly".

I did, but in this line:

scroll = (ScrollViewExt) findViewById(R.id.scrollView1);


it throws a
java.lang.ClassCastException
. I changed the
<ScrollView>
tags in my XML but, obviously, it doesn't work. My questions are: Why, if
ScrollViewExt
extends
ScrollView
, throws to my face a
ClassCastException
? is there any way to detect end of scrolling without messing too much?

Thank you people.

EDIT:
As promised, here is the piece of my XML that matters:

<ScrollView
android:id="@+id/scrollView1"
android:layout_width="match_parent"
android:layout_height="match_parent" >


<WebView
android:id="@+id/textterms"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:gravity="center_horizontal"
android:textColor="@android:color/black" />

</ScrollView>


I changed it from
TextView
to
WebView
to be able of justifying the text inside. What i want to achieve is the "Accept button doesn't activate until the terms of the contract are fully read" thing. My extended class is called
ScrollViewEx
t. If i change the tag
ScrollView
for
ScrollViewExt
it throws an

android.view.InflateException: Binary XML file line #44: Error inflating class ScrollViewExt


because it doesn't understand the tag
ScrollViewEx
. I don't think it has a solution...

Thanks for your answers!

Answer

Did it!

Aside of the fix Alexandre kindly provide me, I had to create an Interface:

public interface ScrollViewListener {
    void onScrollChanged(ScrollViewExt scrollView, 
                         int x, int y, int oldx, int oldy);
}

Then, i had to override the OnScrollChanged method from ScrollView in my ScrollViewExt:

public class ScrollViewExt extends ScrollView {
    private ScrollViewListener scrollViewListener = null;
    public ScrollViewExt(Context context) {
        super(context);
    }

    public ScrollViewExt(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
    }

    public ScrollViewExt(Context context, AttributeSet attrs) {
        super(context, attrs);
    }

    public void setScrollViewListener(ScrollViewListener scrollViewListener) {
        this.scrollViewListener = scrollViewListener;
    }

    @Override
    protected void onScrollChanged(int l, int t, int oldl, int oldt) {
        super.onScrollChanged(l, t, oldl, oldt);
        if (scrollViewListener != null) {
            scrollViewListener.onScrollChanged(this, l, t, oldl, oldt);
        }
    }
}

Now, as Alexandre said, put the package name in the XML tag (my fault), make my Activity class implement the interface created before, and then, put it all together:

scroll = (ScrollViewExt) findViewById(R.id.scrollView1);
scroll.setScrollViewListener(this);

And in the method OnScrollChanged, from the interface...

@Override
public void onScrollChanged(ScrollViewExt scrollView, int x, int y, int oldx, int oldy) {
    // We take the last son in the scrollview
    View view = (View) scrollView.getChildAt(scrollView.getChildCount() - 1);
    int diff = (view.getBottom() - (scrollView.getHeight() + scrollView.getScrollY()));

    // if diff is zero, then the bottom has been reached
    if (diff == 0) {
        // do stuff
    }
}

And it worked!

Thank you very much for your help, Alexandre!

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