OnTabChangeListener Null Pointer

Question

I am attempting to create custom colors of the tabs in a TabHost.

I have impletmented OnTabChangeListener and the MainActivity loads up correctly. However when I click on a new tab I get a null pointer. Where is my error located? I cannot understand what the issue is.

Here is the offending code loosely based off of this example

@Override  
public void onTabChanged(String tabId) {  
     for(int i=0;i<tabHost.getTabWidget().getChildCount();i++)
     {  
        tabHost.getTabWidget().getChildAt(i).setBackgroundDrawable(getResources().getDrawable(R.drawable.greygradient));  
     }
     tabHost.getTabWidget().getChildAt((tabHost.getCurrentTab())).setBackgroundDrawable(getResources().getDrawable(R.drawable.bluegradient));
}

Here is the trace:

06-20 14:27:42.770: E/AndroidRuntime(1490): java.lang.NullPointerException
06-20 14:27:42.770: E/AndroidRuntime(1490):     at com.company.app.MainActivity.onTabChanged(MainActivity.java:72)
06-20 14:27:42.770: E/AndroidRuntime(1490):     at android.widget.TabHost.invokeOnTabChangeListener(TabHost.java:359)
06-20 14:27:42.770: E/AndroidRuntime(1490):     at android.widget.TabHost.setCurrentTab(TabHost.java:344)
06-20 14:27:42.770: E/AndroidRuntime(1490):     at android.widget.TabHost$2.onTabSelectionChanged(TabHost.java:132)
06-20 14:27:42.770: E/AndroidRuntime(1490):     at android.widget.TabWidget$TabClickListener.onClick(TabWidget.java:456)
06-20 14:27:42.770: E/AndroidRuntime(1490):     at android.view.View.performClick(View.java:2485)
06-20 14:27:42.770: E/AndroidRuntime(1490):     at android.view.View$PerformClick.run(View.java:9080)

score 1 · Accepted Answer · edited May 23 '17 at 12:04

1

You should have gone with the StackOverflow example: How do I change the background of an Android tab widget? :-)

@Override  
public void onTabChanged(String tabId) {
    setTabColor(getTabHost());
}

private void setTabColor(TabHost tabhost) {
    for(int i=0;i<tabhost.getTabWidget().getChildCount();i++)
    {
        tabhost.getTabWidget().getChildAt(i).setBackgroundColor(Color.parseColor("#FF0000")); //unselected
    }
    tabhost.getTabWidget().getChildAt(tabhost.getCurrentTab()).setBackgroundColor(Color.parseColor("#0000FF")); // selected
}

The most likely reason for your NullPointer is your TabHost, check that this is being instantiated, I assume you do it within onCreate.

If you are extending TabActivity you can just call getTabHost(); from your Activity context.

edited May 23 '17 at 12:04

Community

1
1

answered Jun 20 '12 at 18:40

Blundell

75,855
30
208
233

Interesting that 45 minutes of searching on SO never brought up that answer, although i've seen similar answers...Anyways your example works, when I try and replace your colors with my drawable gradients i get the null pointer again. Are those structured wrong? – KDEx Jun 20 '12 at 18:49
Solved it, still not sure where the syntax error was (maybe the extra set of () I have in the second line?) Thanks! – KDEx Jun 20 '12 at 18:53

OnTabChangeListener Null Pointer

1 Answers1