Application crashes when i try to save scroll position

Question

My application has an activity which contains many textviews which are used to display a very long block of text so i have divided the text into many textviews. The problem occurs when i try to save the scroll position of the text for orientation changes and to retain the position when the application goes into the background. But when i change the orientation of the screen the application crashes.

Below is the code:

Chapter1.xml

<?xml version="1.0" encoding="utf-8"?>

<ScrollView xmlns:android="http://schemas.android.com/apk/res/android"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:id="@+id/scrollChapter1">
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
                android:layout_width="match_parent"
                android:layout_height="match_parent">
    <TextView
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:text="@string/Chapter1"
            android:textSize="17sp"
            android:padding="10px"
            android:id="@+id/txtChapter1Title"
            />
    <TextView
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:layout_marginTop="15dip"
            android:width="0dip"
            android:textSize="16sp"
            android:padding="10px"
            android:text="@string/Chapter1ContentA"
            android:id="@+id/txtChapter1A"
            android:maxLength="9000"
            android:layout_below="@+id/txtChapter1Title"
            />
    <TextView
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:layout_marginTop="0dip"
            android:width="0dip"
            android:textSize="16sp"
            android:padding="10px"
            android:text="@string/Chapter1ContentB"
            android:id="@+id/txtChapter1B"
            android:maxLength="9000"
            android:layout_below="@+id/txtChapter1A"
            />
    <TextView
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:layout_marginTop="0dip"
            android:width="0dip"
            android:textSize="16sp"
            android:padding="10px"
            android:text="@string/Chapter1ContentC"
            android:id="@+id/txtChapter1C"
            android:maxLength="9000"
            android:layout_below="@+id/txtChapter1B"
            />
    <TextView
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:layout_marginTop="0dip"
            android:width="0dip"
            android:textSize="16sp"
            android:padding="10px"
            android:text="@string/Chapter1ContentD"
            android:id="@+id/txtChapter1D"
            android:maxLength="9000"
            android:layout_below="@+id/txtChapter1C"
            />
    <TextView
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:layout_marginTop="0dip"
            android:width="0dip"
            android:textSize="16sp"
            android:padding="10px"
            android:text="@string/Chapter1ContentE"
            android:id="@+id/txtChapter1E"
            android:maxLength="9000"
            android:layout_below="@+id/txtChapter1D"
            />
    <TextView
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:layout_marginTop="0dip"
            android:width="0dip"
            android:textSize="16sp"
            android:padding="10px"
            android:text="@string/Chapter1ContentF"
            android:id="@+id/txtChapter1F"
            android:maxLength="9000"
            android:layout_below="@+id/txtChapter1E"
            />
    <TextView
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:layout_marginTop="0dip"
            android:width="0dip"
            android:textSize="16sp"
            android:padding="10px"
            android:text="@string/Chapter1ContentG"
            android:id="@+id/txtChapter1G"
            android:maxLength="9000"
            android:layout_below="@+id/txtChapter1F"
            />
</RelativeLayout>
</ScrollView>

Chapter1.java:

public class chapter1 extends Activity {
@Override
public void onCreate(Bundle savedInstanceState){
    super.onCreate(savedInstanceState);
    setContentView(R.layout.chapter1);
    WindowManager w = getWindowManager();
    Display d = w.getDefaultDisplay();
    if(d.getWidth() > d.getHeight()){
        Log.d("Orientation", "Landscape");
    }else{
        Log.d("Orientation", "Potrait");
    }
}
@Override
protected void onSaveInstanceState(Bundle outState){
    super.onSaveInstanceState(outState);
    final ScrollView scrollView = (ScrollView) findViewById(R.id.scrollChapter1);
    final TextView textView = (TextView) scrollView.getChildAt(0); //Crashes at this line
    final int firstVisibleLineOffset = textView.getLayout().getLineForVertical(scrollView.getScrollY());
    final int firstVisibleCharacterOffset = textView.getLayout().getLineStart(firstVisibleLineOffset);
    outState.putInt("ScrollViewContainerTextViewFirstVisibleCharacterOffset", firstVisibleCharacterOffset);
}
@Override
protected void onRestoreInstanceState(Bundle savedInstanceState){
    super.onRestoreInstanceState(savedInstanceState);
    final int firstVisibleCharacterOffset = savedInstanceState.getInt("ScrollViewContainerTextViewFirstVisibleCharacterOffset");
    final ScrollView scrollView = (ScrollView) findViewById(R.id.scrollChapter1);
    scrollView.post(new Runnable() {
        @Override
        public void run() {
            final TextView textView = (TextView) scrollView.getChildAt(0);
            final int firstVisibleLineOffset = textView.getLayout().getLineStart(firstVisibleCharacterOffset);
            final int pixelOffset = textView.getLayout().getLineTop(firstVisibleLineOffset);
            scrollView.scrollTo(0, pixelOffset);
        }
    });
}

}

LogCat:

07-18 15:52:39.921      806-806/com.example.ZindaRud D/Orientation﹕ Potrait
07-18 15:52:41.800      806-810/com.example.ZindaRud D/dalvikvm﹕ GC_CONCURRENT freed 155K, 4% free 7169K/7431K, paused 6ms+6ms
07-18 15:52:41.809      806-806/com.example.ZindaRud D/Orientation﹕ Potrait
07-18 15:52:44.500      806-806/com.example.ZindaRud W/TextLayoutCache﹕ computeValuesWithHarfbuzz -- need to force to single run
07-18 15:52:48.760      806-806/com.example.ZindaRud D/AndroidRuntime﹕ Shutting down VM
07-18 15:52:48.760      806-806/com.example.ZindaRud W/dalvikvm﹕ threadid=1: thread exiting with uncaught exception (group=0x409961f8)
07-18 15:52:48.809      806-806/com.example.ZindaRud E/AndroidRuntime﹕ FATAL EXCEPTION: main
java.lang.ClassCastException: android.widget.RelativeLayout cannot be cast to android.widget.TextView
        at com.example.ZindaRud.chapter1.onSaveInstanceState(chapter1.java:31)
        at android.app.Activity.performSaveInstanceState(Activity.java:1113)
        at android.app.Instrumentation.callActivityOnSaveInstanceState(Instrumentation.java:1185)
        at android.app.ActivityThread.handleRelaunchActivity(ActivityThread.java:3321)
        at android.app.ActivityThread.access$700(ActivityThread.java:122)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1150)
        at android.os.Handler.dispatchMessage(Handler.java:99)
        at android.os.Looper.loop(Looper.java:137)
        at android.app.ActivityThread.main(ActivityThread.java:4340)
        at java.lang.reflect.Method.invokeNative(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:511)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
        at dalvik.system.NativeStart.main(Native Method)

Thanks guys fixed the ClassCastException, but now it does not seem save and retain the scroll position when the orientation changes.

Answer 1

You are getting cast exception and its obvious because you are casting RelativeLayout to a TextView at line

final TextView textView = (TextView) scrollView.getChildAt(0);

ScrollView's immediate child at 0 is RelativeLayout as seen in the Layout.

Answer 2

you have to use it like this sorry for the mistake. Reusing what @micro.pavo sayed

final RelativeLayout rLayout = (RelativeLayout) scrollView.getChildAt(0);
final TextView textView = (TextView) rLayout.getChildAt(0);

or you can access directly

final TextView textView = (TextView)findViewById(R.id.txtChapter1Title);

Answer 3

final TextView textView = (TextView) scrollView.getChildAt(0); //Crashes at this line

RelativeLayout is the child of ScrollView and you are casting it to TextView .

So,

java.lang.ClassCastException: android.widget.RelativeLayout cannot be cast to android.widget.TextView

Answer 4

You are getting a ClassCastException because you are trying to cast a RelativeLayout into TextView on this line

final TextView textView = (TextView) scrollView.getChildAt(0);

As seen in the xml code, the first child under ScrollView is RelativeLayout , try making it something like this:

final RelativeLayout rLayout = (RelativeLayout) scrollView.getChildAt(0);