从主机活动访问ViewPager片段返回片段为NULL [英] Access ViewPager fragment from Host activity returns fragment as NULL
本文介绍了从主机活动访问ViewPager片段返回片段为NULL的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！
问题描述
我试着从主机活动访问ViewPager片段，但 MyFragment1 myFragment1 = (MyFragment1)getSupportFragmentManager().findFragmentByTag(\"android:switcher:\"+R.id.new_pager+\":0\");线返回NULL片段，如何从正确的观点寻呼机片段？
MainActivity：
公共类MainActivity扩展FragmentActivity实现MyFragment1.OnMyFragment1Listener {
@覆盖
公共无效的onCreate（）{
newPagerAdapter =新NewPagerAdapter（getSupportFragmentManager（））; //找到ViewPager
mViewpager =（ViewPager）findViewById（R.id.new_pager）;
mViewpager.setAdapter（newPagerAdapter）;
} @覆盖
公共无效的onsubmit（）{
MyFragment1 myFragment1 =（MyFragment1）getSupportFragmentManager（）findFragmentByTag（机器人：切换：+ R.id.new_pager +0）; //这里myFragment1总是返回NULL
查看rootView = myFragment1.getView（）; }
MyFragment1：
公共类MyFragment1扩展片段{ 私人OnMyFragment1Listener mCallback; / **
*回调接口登录
* /
公共接口OnMyFragment1Listener {
公共无效的onsubmit（）;
} / **
*当连接到主机上的活动该片段被称为
*
* @参数活动
* /
@覆盖
公共无效onAttach（活动活动）{
super.onAttach（活动）; //这将确保集装箱活动实施
//回调interface.If不是，它抛出一个异常 尝试{
mCallback =（OnMyFragment1Listener）活性;
}赶上（抛出ClassCastException E）{
抛出新ClassCastException异常（activity.toString（）+应实现onLoginListener接口）;
}
} @覆盖
公共无效onDetach（）{
super.onDetach（）;
mCallback = NULL;
} 公共MyFragment1（）{
//必需的空公共构造
}
@覆盖
公共查看onCreateView（LayoutInflater充气器，容器的ViewGroup，
捆绑savedInstanceState）{
查看rootView = inflater.inflate（R.layout.fragment_myFragment1，集装箱，FALSE）;
返回rootView;
}
}
更新：
私有类NewInspectionPagerAdapter扩展FragmentStatePagerAdapter实现PagerSlidingTabStrip.IconTabProvider {
SparseArray＆所述;片断＆gt; registeredFragments =新SparseArray＆LT;片断＆gt;（）; 私人最终诠释[]图标= {android.R.drawable.btn_star，android.R.drawable.btn_star，
android.R.drawable.btn_star，android.R.drawable.btn_star};
私人片段resultFragment; 公共NewInspectionPagerAdapter（FragmentManager fragmentManager）{
超（fragmentManager）;
} @覆盖
公共片段的getItem（int i）以{
开关（ⅰ）{
情况下0：
resultFragment =新NewInspectionFragment1（）;
打破;
情况1：
resultFragment =新NewInspectionFragment2（）;
打破;
案例2：
resultFragment =新NewInspectionFragment3（）;
打破;
案例3：
resultFragment =新NewInspectionFragment4（）;
打破;
} 返回resultFragment;
} @覆盖
公众诠释的getCount（）{
返回4;
} @覆盖
公共CharSequence的getPageTitle（INT位置）{
返回对象+（位置+ 1）;
}
@覆盖
公众诠释getPageIconResId（int i）以{
返回图标[I]
} @覆盖
公共对象instantiateItem（ViewGroup中的容器，INT位置）{
片段片段=（片段）super.instantiateItem（集装箱，位置）;
registeredFragments.put（位置，片段）;
返回片段;
} @覆盖
公共无效destroyItem（ViewGroup中的容器，INT位置，Object对象）{
registeredFragments.remove（位置）;
super.destroyItem（集装箱，位置，对象）;
} 公共片段getRegisteredFragment（INT位置）{
返回registeredFragments.get（位置）;
}
}
的onsubmit：
@覆盖
公共无效的onsubmit（）{
NewInspectionPagerAdapter适配器=（NewInspectionPagerAdapter）mViewpager.getAdapter（）;
NewInspectionFragment1 newInspectionFragment1 =（NewInspectionFragment1）adapter.getRegisteredFragment（0）;
//不过newInspectionFragment1返回为NULL
}
解决方案
您可以将您的片段在 fieldvariable 所描述的，当他们被实例化<一个href=\"http://stackoverflow.com/questions/8785221/retrieve-a-fragment-from-a-viewpager\">HERE
只需将片段添加到变量 instantiateItem
@覆盖
公共对象instantiateItem（ViewGroup中的容器，INT位置）{
片段片段=（片段）super.instantiateItem（集装箱，位置）;
registeredFragments.put（位置，片段）;
返回片段;
}
和删除它们在 destroyItem
@覆盖
公共无效destroyItem（ViewGroup中的容器，INT位置，Object对象）{
registeredFragments.remove（位置）;
super.destroyItem（集装箱，位置，对象）;
}
I try to access ViewPager fragment from host activity, but MyFragment1 myFragment1 = (MyFragment1)getSupportFragmentManager().findFragmentByTag("android:switcher:"+R.id.new_pager+":0"); line return NULL fragment,How to get fragment from view pager properly?
MainActivity:
public class MainActivity extends FragmentActivity implements MyFragment1.OnMyFragment1Listener {
@Override
public void onCreate(){
newPagerAdapter = new NewPagerAdapter(getSupportFragmentManager());
// find ViewPager
mViewpager = (ViewPager) findViewById(R.id.new_pager);
mViewpager.setAdapter(newPagerAdapter);
}
@Override
public void onSubmit() {
MyFragment1 myFragment1 = (MyFragment1)getSupportFragmentManager().findFragmentByTag("android:switcher:"+R.id.new_pager+":0");
// Here myFragment1 returns always NULL
View rootView = myFragment1.getView();
}
MyFragment1:
public class MyFragment1 extends Fragment {
private OnMyFragment1Listener mCallback;
/**
* Callback interface for login
*/
public interface OnMyFragment1Listener {
public void onSubmit();
}
/**
* Called when this fragment on attached to the Host Activity
*
* @param activity
*/
@Override
public void onAttach(Activity activity) {
super.onAttach(activity);
// This makes sure that the container activity has implemented
// the callback interface.If not, it throws an exception
try {
mCallback = (OnMyFragment1Listener) activity;
} catch (ClassCastException e) {
throw new ClassCastException(activity.toString() + "should implement onLoginListener interface");
}
}
@Override
public void onDetach() {
super.onDetach();
mCallback = null;
}
public MyFragment1() {
// Required empty public constructor
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_myFragment1, container, false);
return rootView;
}
}
Update:
private class NewInspectionPagerAdapter extends FragmentStatePagerAdapter implements PagerSlidingTabStrip.IconTabProvider {
SparseArray<Fragment> registeredFragments = new SparseArray<Fragment>();
private final int[] ICONS = {android.R.drawable.btn_star, android.R.drawable.btn_star,
android.R.drawable.btn_star, android.R.drawable.btn_star};
private Fragment resultFragment;
public NewInspectionPagerAdapter(FragmentManager fragmentManager) {
super(fragmentManager);
}
@Override
public Fragment getItem(int i) {
switch (i) {
case 0:
resultFragment = new NewInspectionFragment1();
break;
case 1:
resultFragment = new NewInspectionFragment2();
break;
case 2:
resultFragment = new NewInspectionFragment3();
break;
case 3:
resultFragment = new NewInspectionFragment4();
break;
}
return resultFragment;
}
@Override
public int getCount() {
return 4;
}
@Override
public CharSequence getPageTitle(int position) {
return "OBJECT " + (position + 1);
}
@Override
public int getPageIconResId(int i) {
return ICONS[i];
}
@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);
}
}
onSubmit:
@Override
public void onSubmit() {
NewInspectionPagerAdapter adapter = (NewInspectionPagerAdapter)mViewpager.getAdapter();
NewInspectionFragment1 newInspectionFragment1 = (NewInspectionFragment1) adapter.getRegisteredFragment(0);
// Still newInspectionFragment1 returns as NULL
}
解决方案
You can store your fragments in a fieldvariable when they are instantiated as described HERE
Just add the Fragments to the variable in instantiateItem
@Override
public Object instantiateItem(ViewGroup container, int position) {
Fragment fragment = (Fragment) super.instantiateItem(container, position);
registeredFragments.put(position, fragment);
return fragment;
}
and remove them in destroyItem
@Override
public void destroyItem(ViewGroup container, int position, Object object) {
registeredFragments.remove(position);
super.destroyItem(container, position, object);
}
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