public class LazyViewPager extends ViewPager {
private static final float DEFAULT_OFFSET = 0.5f;
private LazyPagerAdapter mLazyPagerAdapter;
private float mInitLazyItemOffset = DEFAULT_OFFSET;
public LazyViewPager(Context context) {
super(context);
}
public LazyViewPager(Context context, AttributeSet attrs) {
super(context, attrs);
TypedArray a = context.obtainStyledAttributes(attrs, R.styleable.LazyViewPager);
setInitLazyItemOffset(a.getFloat(R.styleable.LazyViewPager_init_lazy_item_offset, DEFAULT_OFFSET));
a.recycle();
}
* change the initLazyItemOffset
* @param initLazyItemOffset set mInitLazyItemOffset if {@code 0 < initLazyItemOffset <= 1}
*/
public void setInitLazyItemOffset(float initLazyItemOffset) {
if (initLazyItemOffset > 0 && initLazyItemOffset <= 1) {
mInitLazyItemOffset = initLazyItemOffset;
}
}
@Override
public void setAdapter(PagerAdapter adapter) {
super.setAdapter(adapter);
mLazyPagerAdapter = adapter != null && adapter instanceof LazyPagerAdapter ? (LazyPagerAdapter) adapter : null;
}
@Override
protected void onPageScrolled(int position, float offset, int offsetPixels) {
if (mLazyPagerAdapter != null) {
if (getCurrentItem() == position) {
int lazyPosition = position + 1;
if (offset >= mInitLazyItemOffset && mLazyPagerAdapter.isLazyItem(lazyPosition)) {
mLazyPagerAdapter.startUpdate(this);
mLazyPagerAdapter.addLazyItem(this, lazyPosition);
mLazyPagerAdapter.finishUpdate(this);
}
} else if (getCurrentItem() > position) {
int lazyPosition = position;
if (1 - offset >= mInitLazyItemOffset && mLazyPagerAdapter.isLazyItem(lazyPosition)) {
mLazyPagerAdapter.startUpdate(this);
mLazyPagerAdapter.addLazyItem(this, lazyPosition);
mLazyPagerAdapter.finishUpdate(this);
}
}
}
super.onPageScrolled(position, offset, offsetPixels);
}
}
public abstract class LazyFragmentPagerAdapter extends LazyPagerAdapter<Fragment> {
private static final String TAG = "LazyFragmentPagerAdapter";
private static final boolean DEBUG = false;
private final FragmentManager mFragmentManager;
private FragmentTransaction mCurTransaction = null;
public LazyFragmentPagerAdapter(FragmentManager fm) {
mFragmentManager = fm;
}
@Override
public void startUpdate(ViewGroup container) {
}
@Override
public Object instantiateItem(ViewGroup container, int position) {
if (mCurTransaction == null) {
mCurTransaction = mFragmentManager.beginTransaction();
}
final long itemId = getItemId(position);
String name = makeFragmentName(container.getId(), itemId);
Fragment fragment = mFragmentManager.findFragmentByTag(name);
if (fragment != null) {
if (DEBUG)
Log.v(TAG, "Attaching item #" + itemId + ": f=" + fragment);
mCurTransaction.attach(fragment);
} else {
fragment = getItem(container, position);
if (fragment instanceof Laziable) {
mLazyItems.put(position, fragment);
} else {
mCurTransaction.add(container.getId(), fragment, name);
}
}
if (fragment != getCurrentItem()) {
fragment.setMenuVisibility(false);
fragment.setUserVisibleHint(false);
}
return fragment;
}
@Override
public void destroyItem(ViewGroup container, int position, Object object) {
if (mCurTransaction == null) {
mCurTransaction = mFragmentManager.beginTransaction();
}
if (DEBUG)
Log.v(TAG, "Detaching item #" + getItemId(position) + ": f=" + object + " v=" + ((Fragment) object).getView());
final long itemId = getItemId(position);
String name = makeFragmentName(container.getId(), itemId);
if (mFragmentManager.findFragmentByTag(name) == null) {
mCurTransaction.detach((Fragment) object);
} else {
mLazyItems.remove(position);
}
}
@Override
public Fragment addLazyItem(ViewGroup container, int position) {
Fragment fragment = mLazyItems.get(position);
if (fragment == null)
return null;
final long itemId = getItemId(position);
String name = makeFragmentName(container.getId(), itemId);
if (mFragmentManager.findFragmentByTag(name) == null) {
if (mCurTransaction == null) {
mCurTransaction = mFragmentManager.beginTransaction();
}
mCurTransaction.add(container.getId(), fragment, name);
mLazyItems.remove(position);
}
return fragment;
}
@Override
public void finishUpdate(ViewGroup container) {
if (mCurTransaction != null) {
mCurTransaction.commitAllowingStateLoss();
mCurTransaction = null;
mFragmentManager.executePendingTransactions();
}
}
@Override
public boolean isViewFromObject(View view, Object object) {
return ((Fragment) object).getView() == view;
}
public long getItemId(int position) {
return position;
}
private static String makeFragmentName(int viewId, long id) {
return "android:switcher:" + viewId + ":" + id;
}
* mark the fragment can be added lazily
*/
public interface Laziable {
}
}