android - 滚动时 SherlockFragments 中 ViewPager 的可见性问题(在 Gingerbread 中)

Question

我使用 ViewPager 在 fragment 之间滚动。

在 Gingerbread 上测试时有一个奇怪的问题-

After scrolling first two tabs, the visibility of all fragments GONE completely

这一直持续到我改变方向为止。此问题仅在 Gingerbread 设备启动时出现。它在 ICS 和其他方面运行良好。

这里是TabsAdapter的代码

  /**
 * 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.
 */
private class TabsAdapter extends FragmentPagerAdapter implements
        ViewPager.OnPageChangeListener, ActionBar.TabListener {
    private final Context mContext;
    private final ActionBar mActionBar;
    private final ViewPager mViewPager;
    private final List<String> mTabs = new ArrayList<String>();
    private final List<Integer> mTabsId = new ArrayList<Integer>();
    private boolean hasClearedDetails = false;


    private int mCurrentPosition = -1;
    /**
     * Used during page migration, to remember the next position
     * {@link #onPageSelected(int)} specified.
     */
    private int mNextPosition = -1;

    public TabsAdapter(FragmentActivity activity, ActionBar actionBar, ViewPager pager) {
        super(activity.getSupportFragmentManager());
        mContext = activity;
        mActionBar = actionBar;
        mViewPager = pager;
        mViewPager.setAdapter(this);
        mViewPager.setOnPageChangeListener(this);
    }

    public void addTab(ActionBar.Tab tab, Class<?> clss, int tabId) {
        mTabs.add(clss.getName());
        mTabsId.add(tabId);
        mActionBar.addTab(tab.setTabListener(this));
        notifyDataSetChanged();
    }

    public void removeTabAt(int location) {
        mTabs.remove(location);
        mTabsId.remove(location);
        mActionBar.removeTabAt(location);
        notifyDataSetChanged();
    }

    public Integer getIdForPosition(int position) {
        if(position >= 0 && position < mTabsId.size()) {
            return mTabsId.get(position);
        }
        return null;
    }

    public Integer getPositionForId(int id) {
        int fPos = mTabsId.indexOf(id);
        if(fPos >= 0) {
            return fPos;
        }
        return null;
    }

    @Override
    public int getCount() {
        return mTabs.size();
    }

    @Override
    public Fragment getItem(int position) {
        return Fragment.instantiate(mContext, mTabs.get(position), new Bundle());
    }

    @Override
    public void onTabSelected(Tab tab, FragmentTransaction ft) {
        clearDetails();
        if (mViewPager.getCurrentItem() != tab.getPosition()) {
            Log.e(THIS_FILE+"Anurag debugging","ISSUE HERE");
            mViewPager.setCurrentItem(tab.getPosition(), true);
        }
    }

    @Override
    public void onPageSelected(int position) {
        mActionBar.setSelectedNavigationItem(position);

        if (mCurrentPosition == position) {
            Log.w(THIS_FILE, "Previous position and next position became same (" + position
                    + ")");
            Log.e(THIS_FILE, "Previous position and next position became same (" + position
                    + ")");
        }

        mNextPosition = position;
    }

    @Override
    public void onTabReselected(Tab tab, FragmentTransaction ft) {
        // Nothing to do
    }
    @Override
    public int getItemPosition(Object object){
        return mCurrentPosition;
        }
    @Override
    public void onTabUnselected(Tab tab, FragmentTransaction ft) {
        // Nothing to do
    }

    @Override
    public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
        // Nothing to do
    }

    @Override
    public void onPageScrollStateChanged(int state) {
        switch (state) {
            case ViewPager.SCROLL_STATE_IDLE: {
                Log.e(THIS_FILE, "SCROLL_STATE_IDLE"+mCurrentPosition);
                if (mCurrentPosition >= 0) {
                    sendFragmentVisibilityChange(mCurrentPosition, false);
                }
                if (mNextPosition >= 0) {
                    sendFragmentVisibilityChange(mNextPosition, true);
                }
                invalidateOptionsMenu();

                mCurrentPosition = mNextPosition;
                break;
            }
            case ViewPager.SCROLL_STATE_DRAGGING:
                Log.e(THIS_FILE, "SCROLL_STATE_DRAGGING");
                clearDetails();
                hasClearedDetails = true;
                break;
            case ViewPager.SCROLL_STATE_SETTLING:
                Log.e(THIS_FILE, "SCROLL_STATE_SETTLING");
                hasClearedDetails = false;
                break;
            default:
                break;
        }
    }

    private void clearDetails() {
        if (mDualPane && !hasClearedDetails) {
            Log.e(THIS_FILE, "check in clear detalis");
            FragmentTransaction ft = SipHome.this.getSupportFragmentManager()
                    .beginTransaction();
            ft.replace(R.id.details, new Fragment(), null);
            ft.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_FADE);
            ft.commit();
        }
    }
}

sendFragmentVisibilityChange 的代码是

  private void sendFragmentVisibilityChange(int position, boolean visibility) {
    try {
        final Fragment fragment = getFragmentAt(position);
        if (fragment instanceof ViewPagerVisibilityListener) {
            ((ViewPagerVisibilityListener) fragment).onVisibilityChanged(visibility);
        }
    }catch(IllegalStateException e) {
        Log.e(THIS_FILE, "Fragment not anymore managed");

        e.printStackTrace();
    }catch(Exception e) {
        Log.e(THIS_FILE, "Fragment not anymore managed");

        e.printStackTrace();
    }
}

Fragments 正在调用 onVisibilityChanged 来执行一些滚动操作。这些 fragment 扩展了 SherlockFragment。

提前致谢

Answer 1

使用 setoffscreenpagelimit(int count) 将您的 ViewPager 的 OffscreenPageLimit 设置为您的 ViewPager 实际持有的 View 数。