Programmatically set ActionBarTab background color

问题:

I want to change my ActionBar's Tabs background color with tabs selector line at bottom color.

I want to do that by using java code not xml.

I have tried creating ActionBar tabs ..

actionBar = getActionBar();


// Hide the action bar title
           ActionBar actionBar.setDisplayShowTitleEnabled(false);

        // Enabling Spinner dropdown navigation
        actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);

         ActionBar.Tab PlayerTab = actionBar.newTab().setText("Fragment A");
          ActionBar.Tab StationsTab = actionBar.newTab().setText("Fragment B");

          //create the two fragments we want to use for display content
         //////////////////////// Fragment PlayerFragment = new AFragment();
         /////////////////// Fragment StationsFragment = new BFragment();

          //set the Tab listener. Now we can listen for clicks.
          ///////////////////PlayerTab.setTabListener(new MyTabsListener(PlayerFragment));
         ///////////////// ////StationsTab.setTabListener(new MyTabsListener(StationsFragment));

          //add the two tabs to the actionbar
          actionBar.addTab(PlayerTab);
          actionBar.addTab(StationsTab);

Now when I try to set background color with tabs line selector color, I get the error Java.lang.NullPointException

My OnTabSelcted() method ..

@Override
public void onTabSelected(Tab tab, FragmentTransaction ft) {
// TODO Auto-generated method stub
RelativeLayout tabLayout = (RelativeLayout) tab.getCustomView();

//tab.setCustomView(getResources().getDrawable(R.drawable.tabs_selector_blue));

     System.out.println("Tab position is " +tab.getPosition());
     try{
     if(tab.getCustomView() == null){

tabLayout.setBackgroundResource(TABS_BACKGROUND[tab.getPosition()]);
         tab.setCustomView(tabLayout);
     }else{
         Toast.makeText(getApplicationContext(), "check for tabs", Toast.LENGTH_SHORT).show();
     }
     }catch(Exception e){
         e.printStackTrace();
     }

}

I have defined a custom selector for background and need to inflate it.

I am getting on line tabLayout.setBackgroundResource(TABS_BACKGROUND[tab.getPosition()]);

Please let show me where's my error.

回答1:

I see you are using my solution. Your tabLayout may be null if you didn't initialise it when creating tabs. Here is the code I used to create tabs first, before changing background and text color in onTabSelected

for (int i = 0; i < TABS.length; i++) {
    Tab tab = actionBar.newTab();
    tab.setText(TABS[i]);
    tab.setTabListener(this);
    tab.setCustomView(getTabView(i));  << see getTabView() method below  
    actionBar.addTab(tab, i, (currentTab == i));
}

getTabView() method :

private View getTabView(int i) {
    // TODO Auto-generated method stub
    RelativeLayout r = (RelativeLayout) getLayoutInflater().inflate(
            R.layout.custom_tab, null);
    TextView t = (TextView) r.findViewById(R.id.custom_tab_text);
    t.setText(TABS[i]);
    int color;
    switch (i) {
    case MyObject.TYPE_A:
        color = MyObject.COLOR_A;
        break;
    case MyObject.TYPE_B:
        color = MyObject.B;
        break;
    case MyObject.TYPE_C:
        color = MyObject.COLOR_C;
        break;
    case MyObject.TYPE_E:
        color = MyObject.COLOR_E;
        break;
    case MyObject.TYPE_F:
        color = MyObject.COLOR_F;
        break;
    default:
        color = MyObject.COLOR_A;
        break;
    }

    t.setTextColor(color);
    return r;
}

Finally, custom_tab.xml, the layout of tabs:

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:padding="0dp"
    android:layout_margin="0dp">

    <TextView
        android:id="@+id/custom_tab_text"
        android:layout_width="match_parent"
        android:layout_height="match_parent" 
        android:layout_centerInParent="true"
        android:layout_centerHorizontal="true"
        android:gravity="center|center_horizontal"
        android:textStyle="bold"/>

</RelativeLayout>

回答2:

see the statement

RelativeLayout tabLayout = (RelativeLayout) tab.getCustomView();

and if condition

if(tab.getCustomView() == null){
     tabLayout.setBackgroundResource(TABS_BACKGROUND[tab.getPosition()]);
     tab.setCustomView(tabLayout);
}

Now, if tab.getCustomView() returns null, then tabLayout is also null and the if condition becomes true. and inside if condition, you are referencing tabLayout which is null...