Getting ClassCastException when trying to find out if WebView scrolling has reached end

Question

I'm trying to find out if WebView scroll has reached end. I'm trying to find it by using below code. I'm getting ClassCastException. Please help me out:

This is interface:

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

This is class which extends ScrollView:

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);
    }
}
}

This is my activity class:

public class MainActivity extends Activity implements ScrollViewListener{

ScrollViewExt sv;
WebView wv;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    sv = (ScrollViewExt) findViewById(R.id.scrollTest);
    sv.setScrollViewListener(this);

    wv = (WebView) findViewById(R.id.webTest);
    wv.loadUrl("some url");
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.main, menu);
    return true;
}

@Override
public void onScrollChanged(ScrollViewExt scrollView, int x, int y,
        int oldx, int oldy) {
    // TODO Auto-generated method stub
     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
            System.out.println("in here---->>>");
        }

}

}

This is my layout xml:

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context=".MainActivity" >

    <ScrollView 
        android:id="@+id/scrollTest"
        android:layout_height="600dp"
        android:layout_width="match_parent">
            <WebView 
                android:id="@+id/webTest"
                android:layout_height="600dp"
                android:layout_width="match_parent"/>
    </ScrollView>


</RelativeLayout>

This is my exception:

03-11 10:55:58.744: E/AndroidRuntime(27404): FATAL EXCEPTION: main
03-11 10:55:58.744: E/AndroidRuntime(27404): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.scrolltest/com.example.scrolltest.MainActivity}: java.lang.ClassCastException: android.widget.ScrollView cannot be cast to com.demo.listener.ScrollViewExt
03-11 10:55:58.744: E/AndroidRuntime(27404):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2059)
03-11 10:55:58.744: E/AndroidRuntime(27404):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2084)
03-11 10:55:58.744: E/AndroidRuntime(27404):    at android.app.ActivityThread.access$600(ActivityThread.java:130)
03-11 10:55:58.744: E/AndroidRuntime(27404):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195)
03-11 10:55:58.744: E/AndroidRuntime(27404):    at android.os.Handler.dispatchMessage(Handler.java:99)
03-11 10:55:58.744: E/AndroidRuntime(27404):    at android.os.Looper.loop(Looper.java:137)
03-11 10:55:58.744: E/AndroidRuntime(27404):    at android.app.ActivityThread.main(ActivityThread.java:4745)
03-11 10:55:58.744: E/AndroidRuntime(27404):    at java.lang.reflect.Method.invokeNative(Native Method)
03-11 10:55:58.744: E/AndroidRuntime(27404):    at java.lang.reflect.Method.invoke(Method.java:511)
03-11 10:55:58.744: E/AndroidRuntime(27404):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
03-11 10:55:58.744: E/AndroidRuntime(27404):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
03-11 10:55:58.744: E/AndroidRuntime(27404):    at dalvik.system.NativeStart.main(Native Method)
03-11 10:55:58.744: E/AndroidRuntime(27404): Caused by: java.lang.ClassCastException: android.widget.ScrollView cannot be cast to com.demo.listener.ScrollViewExt
03-11 10:55:58.744: E/AndroidRuntime(27404):    at com.example.scrolltest.MainActivity.onCreate(MainActivity.java:21)
03-11 10:55:58.744: E/AndroidRuntime(27404):    at android.app.Activity.performCreate(Activity.java:5008)
03-11 10:55:58.744: E/AndroidRuntime(27404):    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1079)
03-11 10:55:58.744: E/AndroidRuntime(27404):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2023)
03-11 10:55:58.744: E/AndroidRuntime(27404):    ... 11 more

Answer 1

You have

 <ScrollView  // its a scorllview
    android:id="@+id/scrollTest"

But when you initialize you have

  sv = (ScrollViewExt) findViewById(R.id.scrollTest); 
  // casting to ScrollViewExt which should be ScrollView

If you have ScrollView in xml then initialize it as

  sv = (ScrollView) findViewById(R.id.scrollTest); 

or

  <yourpackagename.ScrollViewExt 
   android:id="@+id/scrollTest"
    android:layout_height="600dp"
    android:layout_width="match_parent">
        <WebView 
            android:id="@+id/webTest"
            android:layout_height="600dp"
            android:layout_width="match_parent"/>
  </yourpackagename.ScrollViewExt >

Answer 2

Instead of using ScrollView in your layout, you have to make your element the fully namespace qualified name of ScrollViewExt

 <com.demo.listener.ScrollViewExt
        android:id="@+id/scrollTest"
        android:layout_height="600dp"
        android:layout_width="match_parent">
            <WebView 
                android:id="@+id/webTest"
                android:layout_height="600dp"
                android:layout_width="match_parent"/>
    </com.demo.listener.ScrollViewExt>

Answer 3

Try to Replace ScrollView in your Xml Layout with ScrollViewExt