フリーランスのAndroid入門

これは、android developer blogのContinuous Shared Element Transitions: RecyclerView to ViewPager 記事を解析した内容になります。

今回のサンプルは、RecyclerViewのGrid形式にして、アイテムをタップするとViewPager形式の
ViewにFadeOutしながら遷移するというもので、
ページビューで遷移元とは異なる画像に切り替えて、Grid画面に戻っても
SharedElementをかけています。

実装方法

まず、グリッド画面となるGridFragmentのonCreateViewで
sharedElementなどのアニメーションの設定をします。

  @Override
  public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container,
      @Nullable Bundle savedInstanceState) {
    recyclerView = (RecyclerView) inflater.inflate(R.layout.fragment_grid, container, false);
    recyclerView.setAdapter(new GridAdapter(this));

    prepareTransitions();
    postponeEnterTransition();

    return recyclerView;
  }

@Override

public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container,

@Nullable Bundle savedInstanceState) {

recyclerView = (RecyclerView) inflater.inflate(R.layout.fragment_grid, container, false);

recyclerView.setAdapter(new GridAdapter(this));

prepareTransitions();

postponeEnterTransition();

return recyclerView;

}

prepareTranstion関数では、fragmentを遷移する時の遷移animationとcallbackの設定をしています。

  /**
   * Prepares the shared element transition to the pager fragment, as well as the other transitions
   * that affect the flow.
   */
  private void prepareTransitions() {
    // Fragmentから遷移する際の遷移アニメーションを設定する
    setExitTransition(TransitionInflater.from(getContext())
        .inflateTransition(R.transition.grid_exit_transition));
    // ...
  }

/**

* Prepares the shared element transition to the pager fragment, as well as the other transitions

* that affect the flow.

private void prepareTransitions() {

// Fragmentから遷移する際の遷移アニメーションを設定する

setExitTransition(TransitionInflater.from(getContext())

.inflateTransition(R.transition.grid_exit_transition));

// ...

}

遷移アニメーション方法はxmlで定義します。

<transitionSet xmlns:android="http://schemas.android.com/apk/res/android"
    android:duration="375"
    android:interpolator="@android:interpolator/fast_out_slow_in"
    android:startDelay="25">
  <fade>
    <targets android:targetId="@id/card_view"/>
  </fade>
</transitionSet>

<transitionSet xmlns:android="http://schemas.android.com/apk/res/android"

android:duration="375"

android:interpolator="@android:interpolator/fast_out_slow_in"

android:startDelay="25">

<fade>

</fade>

</transitionSet>

続いて、GridFragmentからViewPagerに遷移する時とViewPagerからGridFragmentに遷移する際
に呼ばれるSharedElementCallbackクラスのセットと実装をします。

onMapSharedElements関数では、
RecyclerViewと対象のPageViewで表示されるImageの遷移先の設定をmapに埋め込んでいます。

// A similar mapping is set at the ImagePagerFragment with a setEnterSharedElementCallback.
setExitSharedElementCallback(
    new SharedElementCallback() {
      @Override
      public void onMapSharedElements(List<String> names, Map<String, View> sharedElements) {
        // Locate the ViewHolder for the clicked position.
        RecyclerView.ViewHolder selectedViewHolder = recyclerView
            .findViewHolderForAdapterPosition(MainActivity.currentPosition);
        if (selectedViewHolder == null || selectedViewHolder.itemView == null) {
          return;
        }

        // Map the first shared element name to the child ImageView.
        sharedElements
            .put(names.get(0), selectedViewHolder.itemView.findViewById(R.id.card_image));
      }
    });

// A similar mapping is set at the ImagePagerFragment with a setEnterSharedElementCallback.

setExitSharedElementCallback(

new SharedElementCallback() {

@Override

public void onMapSharedElements(List<String> names, Map<String, View> sharedElements) {

// Locate the ViewHolder for the clicked position.

RecyclerView.ViewHolder selectedViewHolder = recyclerView

.findViewHolderForAdapterPosition(MainActivity.currentPosition);

if (selectedViewHolder == null || selectedViewHolder.itemView == null) {

return;

}

// Map the first shared element name to the child ImageView.

sharedElements

.put(names.get(0), selectedViewHolder.itemView.findViewById(R.id.card_image));

}

});

また、ViewPagerが表示されるImagePageFragmentでも同じように遷移先を
SharedElementsにセットしています。

こう設定することで、ViewPagerで他のimageに切り替えた場合でも
ViewPagerで選択したimageをアニメーション対象にすることができます。

private void prepareSharedElementTransition() {
    Transition transition =
            TransitionInflater.from(getContext())
                    .inflateTransition(R.transition.image_shared_element_transition);
    setSharedElementEnterTransition(transition);

    // A similar mapping is set at the GridFragment with a setExitSharedElementCallback.
    setEnterSharedElementCallback(
            new SharedElementCallback() {
                @Override
                public void onMapSharedElements(List<String> names, Map<String, View> sharedElements) {
                    // Locate the image view at the primary fragment (the ImageFragment that is currently
                    // visible). To locate the fragment, call instantiateItem with the selection position.
                    // At this stage, the method will simply return the fragment at the position and will
                    // not create a new one.
                    Fragment currentFragment = (Fragment) viewPager.getAdapter()
                            .instantiateItem(viewPager, MainActivity.currentPosition);
                    View view = currentFragment.getView();
                    if (view == null) {
                        return;
                    }

                    // Map the first shared element name to the child ImageView.
                    sharedElements.put(names.get(0), view.findViewById(R.id.image));
                }
            });
}

private void prepareSharedElementTransition() {

Transition transition =

TransitionInflater.from(getContext())

.inflateTransition(R.transition.image_shared_element_transition);

setSharedElementEnterTransition(transition);

// A similar mapping is set at the GridFragment with a setExitSharedElementCallback.

setEnterSharedElementCallback(

new SharedElementCallback() {

@Override

public void onMapSharedElements(List<String> names, Map<String, View> sharedElements) {

// Locate the image view at the primary fragment (the ImageFragment that is currently

// visible). To locate the fragment, call instantiateItem with the selection position.

// At this stage, the method will simply return the fragment at the position and will

// not create a new one.

Fragment currentFragment = (Fragment) viewPager.getAdapter()

.instantiateItem(viewPager, MainActivity.currentPosition);

View view = currentFragment.getView();

if (view == null) {

return;

}

// Map the first shared element name to the child ImageView.

sharedElements.put(names.get(0), view.findViewById(R.id.image));

}

});

}

遅延遷移をさせる

サンプルでは、urlから画像をloadする際など、
画像が読み込めていない場合のためにpostponeEnterTransition()
により、遅延遷移の設定をしています。

postponeEnterTransition() を読んだ場合に遷移をスタートさせるためには、
startPostponedEnterTransition()を呼びます。

表示されるGrid Imageの1つ1つはFragmentを継承したImageFragmentクラスになっています。

ImageFragmentクラスのonCreateViewでGlideを使って画像を読み込み
読み込みが終了したことを知らせるCallback関数onResouceReady()
または、読み込みが失敗した時に呼ばれるonLoadFailed()で
startPostponedEnterTransition()を呼ぶことにより遅延遷移を実装しています。

public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container,
  @Nullable Bundle savedInstanceState) {
final View view = inflater.inflate(R.layout.fragment_image, container, false);

Bundle arguments = getArguments();
@DrawableRes int imageRes = arguments.getInt(KEY_IMAGE_RES);

// Just like we do when binding views at the grid, we set the transition name to be the string
// value of the image res.
view.findViewById(R.id.image).setTransitionName(String.valueOf(imageRes));

// Load the image with Glide to prevent OOM error when the image drawables are very large.
Glide.with(this)
    .load(imageRes)
    .listener(new RequestListener<Drawable>() {
      @Override
      public boolean onLoadFailed(@Nullable GlideException e, Object model, Target<Drawable>
          target, boolean isFirstResource) {
        // The postponeEnterTransition is called on the parent ImagePagerFragment, so the
        // startPostponedEnterTransition() should also be called on it to get the transition
        // going in case of a failure.
        getParentFragment().startPostponedEnterTransition();
        return false;
      }

      @Override
      public boolean onResourceReady(Drawable resource, Object model, Target<Drawable>
          target, DataSource dataSource, boolean isFirstResource) {
        // The postponeEnterTransition is called on the parent ImagePagerFragment, so the
        // startPostponedEnterTransition() should also be called on it to get the transition
        // going when the image is ready.
        getParentFragment().startPostponedEnterTransition();
        return false;
      }
    })
    .into((ImageView) view.findViewById(R.id.image));
return view;
}

public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container,

@Nullable Bundle savedInstanceState) {

final View view = inflater.inflate(R.layout.fragment_image, container, false);

Bundle arguments = getArguments();

@DrawableRes int imageRes = arguments.getInt(KEY_IMAGE_RES);

// Just like we do when binding views at the grid, we set the transition name to be the string

// value of the image res.

view.findViewById(R.id.image).setTransitionName(String.valueOf(imageRes));

// Load the image with Glide to prevent OOM error when the image drawables are very large.

Glide.with(this)

.load(imageRes)

.listener(new RequestListener<Drawable>() {

@Override

public boolean onLoadFailed(@Nullable GlideException e, Object model, Target<Drawable>

target, boolean isFirstResource) {

// The postponeEnterTransition is called on the parent ImagePagerFragment, so the

// startPostponedEnterTransition() should also be called on it to get the transition

// going in case of a failure.

getParentFragment().startPostponedEnterTransition();

return false;

}

@Override

public boolean onResourceReady(Drawable resource, Object model, Target<Drawable>

target, DataSource dataSource, boolean isFirstResource) {

// The postponeEnterTransition is called on the parent ImagePagerFragment, so the

// startPostponedEnterTransition() should also be called on it to get the transition

// going when the image is ready.

getParentFragment().startPostponedEnterTransition();

return false;

}

})

.into((ImageView) view.findViewById(R.id.image));

return view;

}

sharedElementを使った遷移

RecyclerView.Adapterクラスを継承したGridAdapterクラス内にて、
clickListenerをセットしsharedElementを使った遷移をおこなっています。

まず、ViewPagerからバックキーを押して戻った際にsharedElementを用いた遷移を
行えるように、Activityの位置を保存するためのstatic変数に位置を代入します。

続いて、アニメーションの対象元から自身を除くために、excludeTarget()を呼びます。

最後にFragmentを切り替える際にaddSharedElement()を呼び、sharedElementの設定をし、
commit()を実行します。

  /**
   * Handles a view click by setting the current position to the given {@code position} and
   * starting a {@link  ImagePagerFragment} which displays the image at the position.
   *
   * @param view the clicked {@link ImageView} (the shared element view will be re-mapped at the
   * GridFragment's SharedElementCallback)
   * @param position the selected view position
   */
  @Override
  public void onItemClicked(View view, int position) {
    // Update the position.
    MainActivity.currentPosition = position;

    // Exclude the clicked card from the exit transition (e.g. the card will disappear immediately
    // instead of fading out with the rest to prevent an overlapping animation of fade and move).
    ((TransitionSet) fragment.getExitTransition()).excludeTarget(view, true);

    ImageView transitioningView = view.findViewById(R.id.card_image);
    fragment.getFragmentManager()
        .beginTransaction()
        .setReorderingAllowed(true) // Optimize for shared element transition
        .addSharedElement(transitioningView, transitioningView.getTransitionName())
        .replace(R.id.fragment_container, new ImagePagerFragment(), ImagePagerFragment.class
            .getSimpleName())
        .addToBackStack(null)
        .commit();
  }

/**

* Handles a view click by setting the current position to the given {@code position} and

* starting a {@link ImagePagerFragment} which displays the image at the position.

* @param view the clicked {@link ImageView} (the shared element view will be re-mapped at the

* GridFragment's SharedElementCallback)

* @param position the selected view position

@Override

public void onItemClicked(View view, int position) {

// Update the position.

MainActivity.currentPosition = position;

// Exclude the clicked card from the exit transition (e.g. the card will disappear immediately

// instead of fading out with the rest to prevent an overlapping animation of fade and move).

((TransitionSet) fragment.getExitTransition()).excludeTarget(view, true);

ImageView transitioningView = view.findViewById(R.id.card_image);

fragment.getFragmentManager()

.beginTransaction()

.setReorderingAllowed(true) // Optimize for shared element transition

.addSharedElement(transitioningView, transitioningView.getTransitionName())

.replace(R.id.fragment_container, new ImagePagerFragment(), ImagePagerFragment.class

.getSimpleName())

.addToBackStack(null)

.commit();

}

addSharedFragment

`sharedElement`	`View`: A View in a disappearing Fragment to match with a View in an appearing Fragment.
`name`	`String`: The transitionName for a View in an appearing Fragment to match to the shared element.

遷移対象となるnameは、onBind関数で設定しています。

  void onBind() {
    int adapterPosition = getAdapterPosition();
    setImage(adapterPosition);
    // Set the string value of the image resource as the unique transition name for the view.
    image.setTransitionName(String.valueOf(IMAGE_DRAWABLES[adapterPosition]));
  }

void onBind() {

int adapterPosition = getAdapterPosition();

setImage(adapterPosition);

// Set the string value of the image resource as the unique transition name for the view.

image.setTransitionName(String.valueOf(IMAGE_DRAWABLES[adapterPosition]));

}

PageViewから戻った際にスクロールポジションを合わせる

GridFragmentのonCreatedViewにて、LayoutChangeListenerをセットし、
Activityに保存していたポジションに戻すことでスクロール位置をPageViewで
選択されたイメージの位置に移動させています。

@Override
public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
    super.onViewCreated(view, savedInstanceState);
    scrollToPosition();
}

/**
 * Scrolls the recycler view to show the last viewed item in the grid. This is important when
 * navigating back from the grid.
 */
private void scrollToPosition() {
    recyclerView.addOnLayoutChangeListener(new OnLayoutChangeListener() {
        @Override
        public void onLayoutChange(View v,
                                   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));
            }
        }
    });
}

@Override

public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {

super.onViewCreated(view, savedInstanceState);

scrollToPosition();

}

/**

* Scrolls the recycler view to show the last viewed item in the grid. This is important when

* navigating back from the grid.

private void scrollToPosition() {

recyclerView.addOnLayoutChangeListener(new OnLayoutChangeListener() {

@Override

public void onLayoutChange(View v,

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));

}

});

}

以上になります。

全体のsourceはdeveloper pageのgitを参照ください。
clone先
https://github.com/google/android-transition-examples.git

SharedElement

SharedElementを使ったRecycleViewとViewPagerによるアニメーション画面遷移方法

実装方法

遅延遷移をさせる

sharedElementを使った遷移

addSharedFragment

PageViewから戻った際にスクロールポジションを合わせる

最近の投稿

最近のコメント

アーカイブ

カテゴリー