java - 共享元素转换未正确退出

Question

我有一个 fragment ，我正在从中启动带有 viewpager 的共享元素转换的 Activity ，输入转换工作正常，但是当我在 View 寻呼机中滚动并完成转换时，共享图像来自左侧，这是不需要的应该将自身重新定位到启动的位置，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 Activity 时更新包含 viewpager 的 Activity 中的 View 及其名称，但它与闪烁一起使用:

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 会使用您预定义的 View 开始转换。和transitionName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 View 时，Android 不会知道这一点，并会在返回时保持前一个 View 的转换。因此您需要将更改通知 Android:

• 重新映射过渡属性:使用 setEnterSharedElementCallback更改 transitionName和View从Activity2返回之前到新的.
• 等待Activity1完成渲染addOnPreDrawListener .

最终的实现有点复杂。不过你可以看看我的示例代码https://github.com/tamhuynhit/PhotoGallery 。我尝试实现从许多简单部分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。

我正在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它的方法:

• 覆盖finishAfterTransition在 Activity2 中并调用 setEnterSharedElementCallback方法重新映射 ViewPager 中当前选定的项目。另外，请调用setResult将新选定的索引传递回此处的先前 Activity 。

  @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所以我可以在知道哪个 View 之前设置回调即将被使用。

  @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);
      }
  }
  

• 覆盖onActivityReenter在Activity1中，从结果Intent中获取选定的索引。设置setExitSharedElementCallback重新映射新选定的View当过渡开始时。调用 supportPostponeEnterTransition延迟一下，因为你的新 View此时可能无法渲染。使用getViewTreeObserver().addOnPreDrawListener要监听布局更改，请找到正确的 View按所选索引并继续转换 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 View ，请勿使用 getChildAt或者你得到错误的 View ，使用findViewWithTag相反

在 PagerAdapter.instantiateItem ，使用position作为每个View的标签:

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

    // ...
}

听onPageSelected获取所选索引的事件:

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通过所选索引获取当前 View

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