CODEWITHSUNDEEP
androidscrollview
Giulio Tedesco
Giulio Tedesco

Reputation: 189

How to save and resume ScrollPosition

I need help saving my scrollview's position when resuming the activity. I have a long scrollview containing some buttons. When I click on those buttons, new activities are opened. When I resume the scrollview's activity, the scrollview starts from the top and the user has to scroll again. This is pretty annoying.

How can i save the scrollview position?

I found this, but the line: Util.Log("X:" + scrollX + " Y:" + scrollY); doesn't work:

//  two static variable,
public static int scrollX = 0;
public static int scrollY = -1;

//update & save their value on onPause & onResume.
@Override
protected void onPause()
{
  super.onPause();
  scrollX = scrollView.getScrollX();
  scrollY = scrollView.getScrollY();
}
@Override
protected void onResume()
{
  Util.Log("X:" + scrollX + " Y:" + scrollY);
  super.onResume();
  //this is important. scrollTo doesn't work in main thread.
  scrollView.post(new Runnable()
{
@Override
public void run()
{
  scrollView.scrollTo(scrollX, scrollY);
}
});
}

Thank you for your help! :D

EDIT:

If i remove the line, I'll get this error:

 01-01 17:29:11.023: E/AndroidRuntime(1967): FATAL EXCEPTION: main
01-01 17:29:11.023: E/AndroidRuntime(1967): Process: com.example.appquiz, PID: 1967
01-01 17:29:11.023: E/AndroidRuntime(1967): java.lang.RuntimeException: Unable to resume activity {com.example.appquiz/com.example.appquiz.Categories}: java.lang.NullPointerException
01-01 17:29:11.023: E/AndroidRuntime(1967):     at android.app.ActivityThread.performResumeActivity(ActivityThread.java:2808)
01-01 17:29:11.023: E/AndroidRuntime(1967):     at android.app.ActivityThread.handleResumeActivity(ActivityThread.java:2837)
01-01 17:29:11.023: E/AndroidRuntime(1967):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2270)
01-01 17:29:11.023: E/AndroidRuntime(1967):     at android.app.ActivityThread.access$800(ActivityThread.java:145)
01-01 17:29:11.023: E/AndroidRuntime(1967):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1206)
01-01 17:29:11.023: E/AndroidRuntime(1967):     at android.os.Handler.dispatchMessage(Handler.java:102)
01-01 17:29:11.023: E/AndroidRuntime(1967):     at android.os.Looper.loop(Looper.java:136)
01-01 17:29:11.023: E/AndroidRuntime(1967):     at android.app.ActivityThread.main(ActivityThread.java:5081)
01-01 17:29:11.023: E/AndroidRuntime(1967):     at java.lang.reflect.Method.invokeNative(Native Method)
01-01 17:29:11.023: E/AndroidRuntime(1967):     at java.lang.reflect.Method.invoke(Method.java:515)
01-01 17:29:11.023: E/AndroidRuntime(1967):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:781)
01-01 17:29:11.023: E/AndroidRuntime(1967):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
01-01 17:29:11.023: E/AndroidRuntime(1967):     at dalvik.system.NativeStart.main(Native Method)
01-01 17:29:11.023: E/AndroidRuntime(1967): Caused by: java.lang.NullPointerException
01-01 17:29:11.023: E/AndroidRuntime(1967):     at com.example.appquiz.Categories.onResume(Categories.java:82)
01-01 17:29:11.023: E/AndroidRuntime(1967):     at android.app.Instrumentation.callActivityOnResume(Instrumentation.java:1192)
01-01 17:29:11.023: E/AndroidRuntime(1967):     at android.app.Activity.performResume(Activity.java:5319)
01-01 17:29:11.023: E/AndroidRuntime(1967):     at android.app.ActivityThread.performResumeActivity(ActivityThread.java:2798)
01-01 17:29:11.023: E/AndroidRuntime(1967):     ... 12 more

My entire code:

public static int scrollX = 0;
public static int scrollY = -1;
ScrollView scrollView = (ScrollView) findViewById(R.id.Scrollview);

//blabla

onCreate //...

@Override
protected void onPause() {
// TODO Auto-generated method stub
    scrollX = scrollView.getScrollX();
    scrollY = scrollView.getScrollY();
    super.onPause();
    }

@Override
protected void onResume() {
// TODO Auto-generated method stub
    super.onResume();
    scrollView.post(new Runnable(){
     @Override
     public void run(){
       scrollView.scrollTo(scrollX, scrollY);}});}

Upvotes: 0

Views: 1516

Answers (2)

Nikita Ilyasov
Nikita Ilyasov

Reputation: 500

add this code to the end of your inflateView method and please make sure that R.id.Scrollview is the right Id

scrollView = (ScrollView) findViewById(R.id.Scrollview);

By the way, you should not use post method to do this. The best way to scroll the view is to do the following:

ViewTreeObserver vto = scrollView.getViewTreeObserver();
vto.addOnGlobalLayoutListener(new OnGlobalLayoutListener() {
    public void onGlobalLayout() {
        scrollView.scrollTo(0, 0);
    }
});

If that does not help please tell us what line is this:(com.example.appquiz.Categories.onResume(Categories.java:82))

Upvotes: 3

Pulkit Sethi
Pulkit Sethi

Reputation: 1325

Util.Log("X:" + scrollX + " Y:" + scrollY); remove this code dude this is just logging code and nothing to do with functionality

Upvotes: 0

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