我有一个在 CustomLoader 中抓取网页的活动。加载程序完成后，我想用检索到的数据更新 3 个选项卡的内容。
我正在使用 android dev samples 提供的示例代码来实现活动的 Viewpager/Tabs/Fragments。
当为选项卡创建片段时，正确调用了 onCreateView，视图上的所有小部件都正确定位并映射到变量。
但是，当我尝试从 Activity 中找到片段并调用片段上的方法来更新其内容时，变量为空。此外，调用 getView 也返回 null - 我从 TabsAdapter 检索的片段实例不是正确的实例化实例？
我已将代码缩减为单个选项卡片段，有问题的代码是来自 onLoaderFinished 的调用以更新片段。
所有 3 个选项卡片段都将使用来自单个加载器的数据填充，因此加载器位于活动上，而不是片段上。我只需要一种方法来告诉片段绘制他们的新数据。
public class InfoBloodStocksActivity extends SherlockFragmentActivity
implements LoaderManager.LoaderCallbacks<BloodStocksLoaderResponse> {
TabHost mTabHost;
ViewPager mViewPager;
TabsAdapter mTabsAdapter;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.info_bloodstocks_tabpager);
mTabHost = (TabHost)findViewById(android.R.id.tabhost);
mTabHost.setup();
mViewPager = (ViewPager)findViewById(R.id.infoBloodStocksTabPager);
mViewPager.setOffscreenPageLimit(3);
mTabsAdapter = new TabsAdapter(this, mTabHost, mViewPager);
mTabsAdapter.addTab(mTabHost.newTabSpec("Daily stock").setIndicator("Daily stocks"),
InfoBloodStocksPageFragment.class, null);
if (savedInstanceState != null) {
mTabHost.setCurrentTabByTag(savedInstanceState.getString("tab"));
}
loadStockDetailsFromWebsite();
}
private void loadStockDetailsFromWebsite() {
// Prepare the loader. Either re-connect with an existing one,
// or start a new one.
getSupportLoaderManager().initLoader(0, null, this);
}
@Override
public Loader<BloodStocksLoaderResponse> onCreateLoader(int arg0, Bundle arg1) {
// This is called when a new Loader needs to be created. This
// sample only has one Loader with no arguments, so it is simple.
return new BloodStocksCustomLoader(this);
}
@Override
public void onLoadFinished(Loader<BloodStocksLoaderResponse> loader, BloodStocksLoaderResponse response) {
if (response.isNewStocksLoaded()) {
InfoBloodStocksPageFragment fragment = (InfoBloodStocksPageFragment) mTabsAdapter.getItem(0);
fragment.setNewImage(response.getDailyStocksImageURL());
}
}
@Override
public void onLoaderReset(Loader<BloodStocksLoaderResponse> arg0) {
// TODO Auto-generated method stub
}
@Override
protected void onSaveInstanceState(Bundle outState) {
super.onSaveInstanceState(outState);
outState.putString("tab", mTabHost.getCurrentTabTag());
}
/**
* This is a helper class that implements the management of tabs and all
* details of connecting a ViewPager with associated TabHost. It relies on a
* trick. Normally a tab host has a simple API for supplying a View or
* Intent that each tab will show. This is not sufficient for switching
* between pages. So instead we make the content part of the tab host
* 0dp high (it is not shown) and the TabsAdapter supplies its own dummy
* view to show as the tab content. It listens to changes in tabs, and takes
* care of switch to the correct paged in the ViewPager whenever the selected
* tab changes.
*/
public static class TabsAdapter extends FragmentPagerAdapter
implements TabHost.OnTabChangeListener, ViewPager.OnPageChangeListener {
private final Context mContext;
private final TabHost mTabHost;
private final ViewPager mViewPager;
private final ArrayList<TabInfo> mTabs = new ArrayList<TabInfo>();
static final class TabInfo {
private final String tag;
private final Class<?> clss;
private final Bundle args;
TabInfo(String _tag, Class<?> _class, Bundle _args) {
tag = _tag;
clss = _class;
args = _args;
}
}
static class DummyTabFactory implements TabHost.TabContentFactory {
private final Context mContext;
public DummyTabFactory(Context context) {
mContext = context;
}
@Override
public View createTabContent(String tag) {
View v = new View(mContext);
v.setMinimumWidth(0);
v.setMinimumHeight(0);
return v;
}
}
public TabsAdapter(FragmentActivity activity, TabHost tabHost, ViewPager pager) {
super(activity.getSupportFragmentManager());
mContext = activity;
mTabHost = tabHost;
mViewPager = pager;
mTabHost.setOnTabChangedListener(this);
mViewPager.setAdapter(this);
mViewPager.setOnPageChangeListener(this);
}
public void addTab(TabHost.TabSpec tabSpec, Class<?> clss, Bundle args) {
tabSpec.setContent(new DummyTabFactory(mContext));
String tag = tabSpec.getTag();
TabInfo info = new TabInfo(tag, clss, args);
mTabs.add(info);
mTabHost.addTab(tabSpec);
notifyDataSetChanged();
}
@Override
public int getCount() {
return mTabs.size();
}
@Override
public Fragment getItem(int position) {
TabInfo info = mTabs.get(position);
return Fragment.instantiate(mContext, info.clss.getName(), info.args);
}
@Override
public void onTabChanged(String tabId) {
int position = mTabHost.getCurrentTab();
mViewPager.setCurrentItem(position);
}
@Override
public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
}
@Override
public void onPageSelected(int position) {
// Unfortunately when TabHost changes the current tab, it kindly
// also takes care of putting focus on it when not in touch mode.
// The jerk.
// This hack tries to prevent this from pulling focus out of our
// ViewPager.
TabWidget widget = mTabHost.getTabWidget();
int oldFocusability = widget.getDescendantFocusability();
widget.setDescendantFocusability(ViewGroup.FOCUS_BLOCK_DESCENDANTS);
mTabHost.setCurrentTab(position);
widget.setDescendantFocusability(oldFocusability);
}
@Override
public void onPageScrollStateChanged(int state) {
}
}
}
我正在从活动中调用 setNewImage 。
public class InfoBloodStocksPageFragment extends SherlockFragment {
private ImageView mImageView;
private ProgressBar mProgress;
private TextView mTitle;
private TextView mDescriptionText;
private String mImageURL;
private ImageLoader mImageLoader = ImageLoader.getInstance();
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.info_bloodstocks_page, container, false);
mImageView = (ImageView)view.findViewById(R.id.bloodStocksPageImage);
mProgress = (ProgressBar)view.findViewById(R.id.bloodStocksPageProgress);
mTitle = (TextView)view.findViewById(R.id.bloodStockPageTitle);
mDescriptionText = (TextView)view.findViewById(R.id.bloodStocksPageText);
mProgress.setVisibility(View.VISIBLE);
mDescriptionText.setVisibility(View.GONE);
return view;
}
public void setNewImage(String imageURL) {
// why is mImageView null here ?
// why does getView() return null here ?
View view = getView();
mImageView = (ImageView)view.findViewById(R.id.bloodStocksPageImage);
DisplayImageOptions displayImageOptions = new DisplayImageOptions.Builder()
.showImageForEmptyUri(R.drawable.loading_stock_figures)
.cacheOnDisc()
.imageScaleType(ImageScaleType.EXACT)
.build();
mImageLoader.displayImage(imageURL, mImageView, displayImageOptions, new ImageLoadingListener() {
@Override
public void onLoadingStarted() {
mProgress.setVisibility(View.VISIBLE);
}
@Override
public void onLoadingFailed(FailReason failReason) {
String message = null;
switch (failReason) {
case IO_ERROR:
message = "Input/Output error";
break;
case OUT_OF_MEMORY:
message = "Out Of Memory error";
break;
case UNKNOWN:
message = "Unknown error";
break;
}
mProgress.setVisibility(View.GONE);
mImageView.setImageResource(android.R.drawable.ic_delete);
}
@Override
public void onLoadingComplete() {
mProgress.setVisibility(View.GONE);
Animation anim = AnimationUtils.loadAnimation(getActivity(), R.anim.fade_in);
mImageView.setAnimation(anim);
anim.start();
}
@Override
public void onLoadingCancelled() {
// Do nothing
}
});
}
}