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我是Android开发新手。我正在尝试使用选项卡片段开发应用程序。Android:选项卡片段在预期时未得到初始化
我有三个片段。当我启动应用程序时,调用第一个和第二个片段的onCreateView
方法。选择片段2时(通过滑动或单击选项卡),将调用片段3的onCreateView
。当选择片段三时,没有任何反应。当再次选择片段2(从片段3到片段1)时,调用片段1的onCreateView
。
我想要onCreateView
的片段被调用时,该视图是可见的。 我在这里粘贴我的项目代码。请告诉我发生了什么事。
MainActivity
public class MainActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
// Toolbar and fragments ---- start ---
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
TabLayout tabLayout = (TabLayout) findViewById(R.id.tab_layout);
tabLayout.addTab(tabLayout.newTab().setText("New"));
tabLayout.addTab(tabLayout.newTab().setText("Queue"));
tabLayout.addTab(tabLayout.newTab().setText("About"));
tabLayout.setTabGravity(TabLayout.GRAVITY_FILL);
final ViewPager viewPager = (ViewPager) findViewById(R.id.pager);
final PagerAdapter pagerAdapter = new PagerAdapter
(getSupportFragmentManager(), tabLayout.getTabCount());
viewPager.setAdapter(pagerAdapter);
viewPager.addOnPageChangeListener(new TabLayout.TabLayoutOnPageChangeListener(tabLayout));
tabLayout.setOnTabSelectedListener(new TabLayout.OnTabSelectedListener() {
@Override
public void onTabSelected(TabLayout.Tab tab) {
viewPager.setCurrentItem(tab.getPosition());
}
@Override
public void onTabUnselected(TabLayout.Tab tab) {
}
@Override
public void onTabReselected(TabLayout.Tab tab) {
}
});
}
}
PagerAdapter类
public class PagerAdapter extends FragmentStatePagerAdapter {
int mNumOfTabs;
SparseArray<Fragment> registeredFragments = new SparseArray<Fragment>();
public PagerAdapter(FragmentManager fm, int NumOfTabs) {
super(fm);
this.mNumOfTabs = NumOfTabs;
}
@Override
public Fragment getItem(int position) {
switch (position) {
case 0:
TabFragment1 tab1 = new TabFragment1();
return tab1;
case 1:
TabFragment2 tab2 = new TabFragment2();
return tab2;
case 2:
TabFragment3 tab3 = new TabFragment3();
return tab3;
default:
return null;
}
}
@Override
public int getCount() {
return mNumOfTabs;
}
@Override
public Object instantiateItem(ViewGroup container, int position) {
Fragment fragment = (Fragment) super.instantiateItem(container, position);
registeredFragments.put(position, fragment);
return fragment;
}
@Override
public void destroyItem(ViewGroup container, int position, Object object) {
registeredFragments.remove(position);
super.destroyItem(container, position, object);
}
public Fragment getRegisteredFragment(int position) {
return registeredFragments.get(position);
}
}
Fragement(所有片段具有相同的代码只吐司文本的变化)
public class TabFragment3 extends Fragment {
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
Toast.makeText(getActivity().getApplicationContext(),"333",Toast.LENGTH_LONG).show();
return inflater.inflate(R.layout.tab_fragment_3, container, false);
}
}
调用它两次是好的。但是也想在时间片视图变得可见时调用onCreateView。 – User42