Android: Making a button visible once webview is done scrolling

Question

I have a webview which shows an html file. When the user scrolls to the bottom of this file in webview, I want a button that was previously hidden to show up, which the user can then press to do some activity

I did something similar in iOS, where I just set the delegate to the ViewController and just set the button as visible. How do I do something similar on Android? I noticed there isn't a callback method like in iOS.

Edit: Right now, I have an activity with 2 objects: a webview containing my text, and a button which is currently invisible. I want my activity to receive a message when the webview text scrolls to the bottom, and make the button visible

Answer 1

I had to do this myself, in order to display an "I Agree" button once the user has scrolled to the bottom of a EULA. Lawyers, huh?

In fact when you override the WebView (rather than the ScrollView as in the answer from @JackTurky) you can call computeVerticalScrollRange() to get the height of the content, rather than getBottom() which returns the visible bottom and is not useful.

This is my comprehensive solution. As far as I can see this is all API Level 1 stuff, so it should work anywhere.

public class EulaWebView extends WebView {
    public EulaWebView(Context context) 
    {
        this(context, null);
    }

    public EulaWebView(Context context, AttributeSet attrs) 
    {
        this(context, attrs, 0);
    }

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

    public OnBottomReachedListener mOnBottomReachedListener = null;
    private int mMinDistance = 0;

    /**
     * Set the listener which will be called when the WebView is scrolled to within some
     * margin of the bottom.
     * @param bottomReachedListener
     * @param allowedDifference
     */
    public void setOnBottomReachedListener(OnBottomReachedListener bottomReachedListener, int allowedDifference ) {
        mOnBottomReachedListener = bottomReachedListener;
        mMinDistance = allowedDifference;
    }

    /**
     * Implement this interface if you want to be notified when the WebView has scrolled to the bottom.
     */
    public interface OnBottomReachedListener {
        void onBottomReached(View v);
    }

    @Override
    protected void onScrollChanged(int left, int top, int oldLeft, int oldTop) {
        if ( mOnBottomReachedListener != null ) {
            if ( (computeVerticalScrollRange() - (top + getHeight())) <= mMinDistance )
                mOnBottomReachedListener.onBottomReached(this);
        }
        super.onScrollChanged(left, top, oldLeft, oldTop);
    }

}

I use this to display an "I Agree" button once the user has scrolled to the bottom of the WebView, where I call it like this (in a class which "implements OnBottomReachedListener":

EulaWebView mEulaContent;
Button mEulaAgreed;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    setContentView(R.layout.eula);
    mEulaContent = (EulaWebView) findViewById(R.id.eula_content);
    StaticHelpers.loadWebView(this, mEulaContent, R.raw.stylesheet, StaticHelpers.readRawTextFile(this, R.raw.eula), null);
    mEulaContent.setVerticalScrollBarEnabled(true);
    mEulaContent.setOnBottomReachedListener(this, 50);

    mEulaAgreed = (Button) findViewById(R.id.eula_agreed);
    mEulaAgreed.setOnClickListener(this);
    mEulaAgreed.setVisibility(View.GONE);
}

@Override
public void onBottomReached(View v) {
    mEulaAgreed.setVisibility(View.VISIBLE);
}

So when the bottom is reached (or in this case, when they get within 50 pixels of it) the "I Agree" button appears.

Answer 2

[I can't comment on an answer, so leaving my comment here as a new answer]

karora's answer (the first) works very well, except that in the

protected void onScrollChanged(int left, int top, int oldLeft, int oldTop)

method, calling

getContentHeight()

was wildly inaccurate for me. It reported a value much too small, so my listener was called when the user had only scrolled maybe a third of the way down the WebView. I used

computeVerticalScrollRange()

instead, and that is perfect. Thanks to this post for that helpful hint.