共享元素转换未正确退出

Question

Intent myIntent = new Intent(getActivity(), EnlargeActivity.class);

            ActivityOptionsCompat options = ActivityOptionsCompat.
                    makeSceneTransitionAnimation(getActivity(),
                            imageView,
                            ViewCompat.getTransitionName(imageView));
            startActivity(myIntent, options.toBundle());

当完成活动时，我正在更新包含viewpager的活动中的视图及其名称，但它会闪烁：

public void finishAfterTransition() {
    setEnterSharedElementCallback(new SharedElementCallback() {
        @Override
        public void onMapSharedElements(List<String> names, Map<String, View> sharedElements) {
            // Clear all current shared views and names
            names.clear();
            sharedElements.clear();

            ViewGroup viewGroup = (ViewGroup) viewPagerDetail.getAdapter()
                    .instantiateItem(viewPagerDetail, viewPagerDetail.getCurrentItem());

            if (viewGroup == null) {
                return;
            }

            // Map the first shared element name to the child ImageView.
            sharedElements.put(viewGroup.findViewById(R.id.img).getTransitionName(), viewGroup.findViewById(R.id.img));

           // setExitSharedElementCallback((SharedElementCallback) this);
        }
    });

    super.finishAfterTransition();

Answer 1

基本上，Android使用预定义的视图和transitionname开始转换，并自动将相同的属性用于返回转换。当你在ViewPager中改变你的聚焦视图时，Android并不知道这一点，而是在返回的路上保持上一个的转换。因此您需要通知Android有关更改：

• 重新映射转换属性：在从Activity2返回之前，使用SetEnterShareDelementCallback将TransitionName和视图更改为新的。
• 等待Activity1完成呈现AddonPredrawListener。

在最终实现中有点复杂。但是您可以查看我的示例代码https://github.com/tamhuynhit/photogally。我试图实现从许多简单节到复杂节的共享元素转换。您的问题出现在级别3中，并在级别4中解决。

更新1：工作流程

下面是我如何在代码中实现它：

>

在Activity2中重写FinishafterTransition，并调用SetEnterShareDelementCallback方法在ViewPager中重新映射当前选定的项。另外，调用setresult将新选择的索引传递回此处的上一个活动。

@Override 
@TargetApi(Build.VERSION_CODES.LOLLIPOP) 
public void finishAfterTransition() {
    setEnterSharedElementCallback(new SharedElementCallback() {
        @Override
        public void onMapSharedElements(List<String> names, Map<String, View> sharedElements) {
            View selectedView = getSelectedView();
            if (selectedView == null)
                return;

            // Clear all current shared views and names
            names.clear();
            sharedElements.clear();

            // Store new selected view and name
            String transitionName = ViewCompat.getTransitionName(selectedView);
            names.add(transitionName);
            sharedElements.put(transitionName, selectedView);

            setExitSharedElementCallback((SharedElementCallback) null);
        }
    });

    Intent intent = new Intent();
    intent.putExtra(PHOTO_FOCUSED_INDEX, mCurrentIndex);
    setResult(RESULT_PHOTO_CLOSED, intent);

    super.finishAfterTransition();
}

编写一个自定义的ShareElementCallback，这样我就可以在知道要使用哪个视图之前设置回调。

@TargetApi(Build.VERSION_CODES.LOLLIPOP)
private static class CustomSharedElementCallback extends SharedElementCallback {
    private View mView;

    /**
     * Set the transtion View to the callback, this should be called before starting the transition so the View is not null
     */
    public void setView(View view) {
        mView = view;
    }

    @Override
    public void onMapSharedElements(List<String> names, Map<String, View> sharedElements) {
        // Clear all current shared views and names
        names.clear();
        sharedElements.clear();

        // Store new selected view and name
        String transitionName = ViewCompat.getTransitionName(mView);
        names.add(transitionName);
        sharedElements.put(transitionName, mView);
    }
}

在Activity1中重写onActivityReenter，从结果Intent中获取选定的索引。设置SetExitShareDelementCallback以在转换开始时重新映射新的选定视图。调用SupportPostponeEntertransition以延迟一点，因为此时可能无法呈现新的视图。使用GetViewTreeObserver().AddonPredrawListener侦听布局更改，根据所选索引找到正确的视图并继续转换SupportStartPostponedEnterTransition。

@Override
@TargetApi(Build.VERSION_CODES.LOLLIPOP)
public void onActivityReenter(int resultCode, Intent data) {
    if (resultCode != LevelFourFullPhotoActivity.RESULT_PHOTO_CLOSED || data == null)
        return;

    final int selectedIndex = data.getIntExtra(LevelFourFullPhotoActivity.PHOTO_FOCUSED_INDEX, -1);
    if (selectedIndex == -1)
        return;

    // Scroll to the new selected view in case it's not currently visible on the screen
    mPhotoList.scrollToPosition(selectedIndex);

    final CustomSharedElementCallback callback = new CustomSharedElementCallback();
    getActivity().setExitSharedElementCallback(callback);

    // Listen for the transition end and clear all registered callback
    getActivity().getWindow().getSharedElementExitTransition().addListener(new Transition.TransitionListener() {
        @Override
        public void onTransitionStart(Transition transition) {}

        @Override
        public void onTransitionPause(Transition transition) {}

        @Override
        public void onTransitionResume(Transition transition) {}

        @Override
        public void onTransitionEnd(Transition transition) {
            removeCallback();
        }

        @Override
        public void onTransitionCancel(Transition transition) {
            removeCallback();
        }

        private void removeCallback() {
            if (getActivity() != null) {
                getActivity().getWindow().getSharedElementExitTransition().removeListener(this);
                getActivity().setExitSharedElementCallback((SharedElementCallback) null);
            }
        }
    });

    // Pause transition until the selected view is fully drawn
    getActivity().supportPostponeEnterTransition();

    // Listen for the RecyclerView pre draw to make sure the selected view is visible,
    //  and findViewHolderForAdapterPosition will return a non null ViewHolder
    mPhotoList.getViewTreeObserver().addOnPreDrawListener(new ViewTreeObserver.OnPreDrawListener() {
        @Override
        public boolean onPreDraw() {
            mPhotoList.getViewTreeObserver().removeOnPreDrawListener(this);

            RecyclerView.ViewHolder holder = mPhotoList.findViewHolderForAdapterPosition(selectedIndex);
            if (holder instanceof ViewHolder) {
                callback.setView(((ViewHolder) holder).mPhotoImg);
            }

            // Continue the transition
            getActivity().supportStartPostponedEnterTransition();

            return true;
        }
    });
}

更新2:getSelectedItem

若要从视图页获取选定视图，请不要使用getchildat，否则获取的视图是错误的，请使用findviewwithtag

在PagerAdapter.InstantiateItem中，将position用作每个视图的标记：

@Override
public View instantiateItem(ViewGroup container, int position) {
    // Create the View
    view.setTag(position)

    // ...
}

mViewPager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {
    @Override
    public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {

    }

    @Override
    public void onPageSelected(int position) {
        mSelectedIndex = position;
    }

    @Override
    public void onPageScrollStateChanged(int state) {

    }
});

private View getSelectedView() {
    try {
        return mPhotoViewPager.findViewWithTag(mSelectedIndex);
    } catch (IndexOutOfBoundsException | NullPointerException ex) {
        return null;
    }
}