Question

我有片段，我正在启动具有viewpager的共享元素转换的活动，输入转换工作正常但是当我在视图寻呼机中滚动并完成转换时，共享图像来自左侧，这是不希望的应该将自己重新定位到它的启动位置，这是我的代码：

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

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

我在完成活动时在包含viewpager的活动中更新视图及其名称，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

这实际上是一种默认行为，我在很多方面都在努力争取SharedElementTransitions，但我已经嵌套了片段。我从一篇文章（最近的文章）中得到了我的解决方案，它显示了一个RecyclerView的实现，我猜你有。简而言之，解决方案是覆盖onLayoutChange：

recyclerView.addOnLayoutChangeListener(
new OnLayoutChangeListener() {
  @Override
  public void onLayoutChange(View view,
            int left, 
            int top, 
            int right, 
            int bottom, 
            int oldLeft, 
            int oldTop, 
            int oldRight, 
            int oldBottom) {
     recyclerView.removeOnLayoutChangeListener(this);
     final RecyclerView.LayoutManager layoutManager =
        recyclerView.getLayoutManager();
     View viewAtPosition = 
        layoutManager.findViewByPosition(MainActivity.currentPosition);
     // Scroll to position if the view for the current position is null (not   
     // currently part of layout manager children), or it's not completely
     // visible.
     if (viewAtPosition == null 
         || layoutManager.isViewPartiallyVisible(viewAtPosition, false, true)){
        recyclerView.post(() 
           -> layoutManager.scrollToPosition(MainActivity.currentPosition));
     }
 }
});

以下是article，您还可以在GitHub找到该项目。

Answer 2

基本上，Android会使用预定义的View和transitionName启动转换，并自动使用相同的属性进行返回转换。当您在ViewPager中更改焦点视图时，Android不知道这一点，并在返回途中保持对前一个的转换。因此，您需要告知Android有关更改的信息：

重新映射过渡属性：在从setEnterSharedElementCallback返回之前，使用transitionName将View和Activity2更改为新属。
等待Activity1完成呈现addOnPreDrawListener。

最终实施中有点复杂。但是你可以查看我的示例代码https://github.com/tamhuynhit/PhotoGallery。我尝试实现从许多简单到复杂部分的共享元素转换。您的问题出现在Level 3，并在Level 4中解决了。

我正在编写一个关于此的教程，但它不是英文的，所以希望代码可以提供帮助

更新1：工作流程

以下是我在代码中实现的方法：

覆盖Activity2中的finishAfterTransition并调用setEnterSharedElementCallback方法重新映射ViewPager中当前选定的项目。此外，请致电setResult将新选定的索引传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();
}

编写自定义ShareElementCallback，以便我可以在知道将要使用哪个View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中覆盖onActivityReenter，从结果Intent中获取所选索引。设置setExitSharedElementCallback以在转换开始时重新映射新选定的View。请supportPostponeEnterTransition稍稍延迟，因为此时可能无法呈现新的View。使用getViewTreeObserver().addOnPreDrawListener来监听布局更改，找到所选索引的正确View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

要从ViewPager获取选定的视图，请不要使用getChildAt，否则您的视图会显示错误，请改用findViewWithTag

在PagerAdapter.instantiateItem中，使用position作为每个视图的标记：

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

    // ...
}

收听onPageSelected事件以获取所选索引：

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) {

    }
});

调用getSelectedView以获取所选索引的当前视图

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

共享元素转换未正确退出

2 个答案: