我有一个Activity来处理一些标签和一些片段,它们是标签的视图。每当我从我的片段调用一个Activity方法时,我的Activity类中的actionbar变量都为null。
我的一个片段调用位于Activity中的方法:
mainActivity.updateTabTitles(0, 5);
活动内部的是:
private ActionBar actionBar; // nitialized inside of OnCreate() as actionBar = getActionBar();
public void updateTabTitles(int pageNum, int remaining) {
String text = tabs[pageNum] + " (" + remaining + ")";
actionBar.getTabAt(pageNum).setText(text); // actionBar is NULL? NullPointerException
}
为什么当我的片段调用我的activity方法时,actionbar为null,但从来没有?
活动代码:
@TargetApi(Build.VERSION_CODES.HONEYCOMB)
public class MainActivity extends FragmentActivity implements ActionBar.TabListener {
private ViewPager viewPager;
private TabsPagerAdapter mAdapter;
private ActionBar actionBar;
// Tab titles
private String[] tabs = {"Pre-arrival Plan", "Primary Survey", "Secondary Survey"};
@TargetApi(Build.VERSION_CODES.ICE_CREAM_SANDWICH)
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
// Initialization
viewPager = (ViewPager) findViewById(R.id.pager);
actionBar = getActionBar();
mAdapter = new TabsPagerAdapter(getSupportFragmentManager());
viewPager.setAdapter(mAdapter);
actionBar.setHomeButtonEnabled(false);
actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);
// Adding Tabs
for (String tab_name : tabs) {
actionBar.addTab(actionBar.newTab().setText(tab_name).setTabListener(this));
}
/**
* on swiping the viewpager make respective tab selected
* */
viewPager.setOnPageChangeListener(new ViewPager.OnPageChangeListener() {
@Override
public void onPageSelected(int position) {
// on changing the page
// make respected tab selected
actionBar.setSelectedNavigationItem(position);
}
@Override
public void onPageScrolled(int arg0, float arg1, int arg2) {
}
@Override
public void onPageScrollStateChanged(int arg0) {
}
});
updateTabTitles(0, 12);
updateTabTitles(1, 2);
updateTabTitles(2, 14);
}
public void updateTabTitles(int pageNum, int remaining) {
String text = tabs[pageNum] + " (" + remaining + ")";
System.out.println(actionBar); // Null
actionBar.getTabAt(pageNum).setText(text);
}
@Override
public void onTabSelected(ActionBar.Tab tab, FragmentTransaction ft) {
viewPager.setCurrentItem(tab.getPosition());
}
@Override
public void onTabUnselected(ActionBar.Tab tab, FragmentTransaction ft) {
}
@Override
public void onTabReselected(ActionBar.Tab tab, FragmentTransaction ft) {
}
};
答案 0 :(得分:0)
要从Fragment调用容器Activity上的方法,你应该这样做:
((MainActivity) getActivity()).updateTabTitles(0, 5);