在viewpager中获取当前片段实例
在viewpager中获取当前片段实例
提问于 2013-09-04 16:46:52
下面是我的代码，其中每个3 Fragment classes都嵌入了ViewPager上的3个选项卡。我有一个菜单选项。如onOptionsItemSelected()所示，通过选择一个选项，我需要更新当前可见的片段。为了更新它，我必须调用fragment类中的一个方法。有没有人能建议一下如何调用这个方法？
public class MainActivity extends ActionBarActivity {
ViewPager ViewPager;
TabsAdapter TabsAdapter;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
ViewPager = new ViewPager(this);
ViewPager.setId(R.id.pager);
setContentView(ViewPager);
final ActionBar bar = getSupportActionBar();
bar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);
//Attaching the Tabs to the fragment classes and setting the tab title.
TabsAdapter = new TabsAdapter(this, ViewPager);
TabsAdapter.addTab(bar.newTab().setText("FragmentClass1"),
FragmentClass1.class, null);
TabsAdapter.addTab(bar.newTab().setText("FragmentClass2"),
FragmentClass2.class, null);
TabsAdapter.addTab(bar.newTab().setText("FragmentClass3"),
FragmentClass3.class, null);
if (savedInstanceState != null) {
bar.setSelectedNavigationItem(savedInstanceState.getInt("tab", 0));
}
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
switch (item.getItemId()) {
case R.id.addText:
**// Here I need to call the method which exists in the currently visible Fragment class**
return true;
}
return super.onOptionsItemSelected(item);
}
@Override
protected void onSaveInstanceState(Bundle outState) {
super.onSaveInstanceState(outState);
outState.putInt("tab", getSupportActionBar().getSelectedNavigationIndex());
}
public static class TabsAdapter extends FragmentPagerAdapter
implements ActionBar.TabListener, ViewPager.OnPageChangeListener {
private final Context mContext;
private final ActionBar mActionBar;
private final ViewPager mViewPager;
private final ArrayList<TabInfo> mTabs = new ArrayList<TabInfo>();
static final class TabInfo {
private final Class<?> clss;
private final Bundle args;
TabInfo(Class<?> _class, Bundle _args) {
clss = _class;
args = _args;
}
}
public TabsAdapter(ActionBarActivity activity, ViewPager pager) {
super(activity.getSupportFragmentManager());
mContext = activity;
mActionBar = activity.getSupportActionBar();
mViewPager = pager;
mViewPager.setAdapter(this);
mViewPager.setOnPageChangeListener(this);
}
public void addTab(ActionBar.Tab tab, Class<?> clss, Bundle args) {
TabInfo info = new TabInfo(clss, args);
tab.setTag(info);
tab.setTabListener(this);
mTabs.add(info);
mActionBar.addTab(tab);
notifyDataSetChanged();
}
@Override
public void onPageScrollStateChanged(int state) {
// TODO Auto-generated method stub
}
@Override
public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
// TODO Auto-generated method stub
}
@Override
public void onPageSelected(int position) {
// TODO Auto-generated method stub
mActionBar.setSelectedNavigationItem(position);
}
@Override
public void onTabReselected(Tab tab, FragmentTransaction ft) {
// TODO Auto-generated method stub
}
@Override
public void onTabSelected(Tab tab, FragmentTransaction ft) {
Object tag = tab.getTag();
for (int i=0; i<mTabs.size(); i++) {
if (mTabs.get(i) == tag) {
mViewPager.setCurrentItem(i);
}
}
tabPosition = tab.getPosition();
}
@Override
public void onTabUnselected(Tab tab, FragmentTransaction ft) {
// TODO Auto-generated method stub
}
@Override
public Fragment getItem(int position) {
TabInfo info = mTabs.get(position);
return Fragment.instantiate(mContext, info.clss.getName(), info.args);
}
@Override
public int getCount() {
return mTabs.size();
}
}
}假设下面的片段类包含我想要调用的方法updateList()：
public class FragmentClass1{
ArrayList<String> originalData;
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View fragmentView = inflater.inflate(R.layout.frag1, container, false);
originalData = getOriginalDataFromDB();
return fragmentView;
}
public void updateList(String text)
{
originalData.add(text);
//Here I could do other UI part that need to added
}
}回答 23
Stack Overflow用户
发布于 2014-01-14 08:36:40
public class MyPagerAdapter extends FragmentPagerAdapter {
private Fragment mCurrentFragment;
public Fragment getCurrentFragment() {
return mCurrentFragment;
}
//...
@Override
public void setPrimaryItem(ViewGroup container, int position, Object object) {
if (getCurrentFragment() != object) {
mCurrentFragment = ((Fragment) object);
}
super.setPrimaryItem(container, position, object);
}
}Stack Overflow用户
发布于 2013-09-04 17:19:47
首先，跟踪所有的“活动”片段页面。在本例中，跟踪ViewPager使用的FragmentStatePagerAdapter中的片段页面。
@Override
public Fragment getItem(int index) {
Fragment myFragment = MyFragment.newInstance();
mPageReferenceMap.put(index, myFragment);
return myFragment;
}为了避免引用“非活动”片段页面，您需要实现FragmentStatePagerAdapter的destroyItem(...)方法：
@Override
public void destroyItem (ViewGroup container, int position, Object object) {
super.destroyItem(container, position, object);
mPageReferenceMap.remove(position);
}当您需要访问当前可见的页面时，您可以调用：
int index = mViewPager.getCurrentItem();
MyAdapter adapter = ((MyAdapter)mViewPager.getAdapter());
MyFragment fragment = adapter.getFragment(index);其中MyAdapter的getFragment(int)方法如下所示：
public MyFragment getFragment(int key) {
return mPageReferenceMap.get(key);
}希望它能有所帮助！
Stack Overflow用户
发布于 2013-09-04 19:21:12
这是我不能为特定片段类的实例变量获取NullPointerException的唯一方式。这可能会对其他坚持做同样事情的人有所帮助。在onOptionsItemSelected()中，我按照以下方式编写代码：
if(viewPager.getCurrentItem() == 0) {
FragmentClass1 frag1 = (FragmentClass1)viewPager
.getAdapter()
.instantiateItem(viewPager, viewPager.getCurrentItem());
frag1.updateList(text);
} else if(viewPager.getCurrentItem() == 1) {
FragmentClass2 frag2 = (FragRecentApps)viewPager
.getAdapter()
.instantiateItem(viewPager, viewPager.getCurrentItem());
frag2.updateList(text);
}页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/18609261
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