android - 获取 fragment 宽度，viewtreeobserver 监听器不工作

Question

我有一个 fragment 可以在细节 Activity 中(如果设备的视口(viewport)很小)或在主要 Activity 中(如果视口(viewport)很大，例如平板电脑)。

fragment 内部有一个 ImageView，我需要根据 fragment 的宽度调整其大小。我做了一些研究，发现实现此目的的“规范”方法是向 viewtreeobserver 添加一个监听器。但是，由于某种原因，它不起作用:

这是我的 fragment :

public class MediaDetailFragment extends Fragment implements DetailsMvpView {

    private static final String RESOURCE = "resource";

    @Inject DetailPresenter mPresenter;
    @BindView(R.id.media_image_flipper)
    ViewFlipper mImageFlipper;
    @BindView(R.id.title_textview)
    TextView mTitleTextView;
    @BindView(R.id.button_share)
    ImageButton mShare;
    @BindView(R.id.button_trailers) ImageButton mTrailers;
    @BindView(R.id.keyword_recyclerview)
    RecyclerView mKeywordRecyclerView;
    @BindView(R.id.overview_content_textview) TextView mOverviewTextView;
    @BindView(R.id.main_image_holder) ViewGroup mImageHolder;
    @BindView(R.id.parent_cardview)
    CardView mParentCardView;

    @BindString(R.string.youtube_base_url) String mYoutubeUrl;
    @BindBool(R.bool.isTablet) boolean mIsTablet;

    private Media mMedia;
    private DisplayMetrics mDisplayMetrics = new DisplayMetrics();

    public static MediaDetailFragment insertOnTarget(AppCompatActivity activity, int target, Media media) {
        MediaDetailFragment fragment = MediaDetailFragment.instantiateWithArguments(media);
        FragmentManager fm = activity.getSupportFragmentManager();
        fm.beginTransaction()
                .replace(target, fragment)
                .setCustomAnimations(android.R.anim.slide_in_left, android.R.anim.slide_out_right)
                .commit();
        return fragment;
    }

    @Override
    public void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        mMedia = getArguments().getParcelable(RESOURCE);
    }

    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container,
                             @Nullable Bundle savedInstanceState) {

        View rootView = inflater.inflate(R.layout.media_details_fragment, container, false);
        ((BaseActivity)getActivity()).activityComponent().inject(this);
        ButterKnife.bind(this, rootView);

        getActivity().getWindowManager().getDefaultDisplay().getMetrics(mDisplayMetrics);



        mTitleTextView.setText(mMedia.title());
        mOverviewTextView.setText(mMedia.overview());

        mKeywordRecyclerView.setAdapter(new KeywordAdapter(getContext()));

        return rootView;
    }

    @Override
    public void onActivityCreated(@Nullable Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);

        final View view = getView();
        if (view == null) return;
        view.getViewTreeObserver().addOnGlobalLayoutListener(() -> {
            if (mIsTablet) {
                mImageFlipper.getLayoutParams().height =
                        ViewUtil.setHeightForAspectRatio(view.getWidth(), ViewUtil.PORTRAIT);
            } else {
                mImageFlipper.getLayoutParams().height =
                        ViewUtil.setHeightForAspectRatio(mDisplayMetrics.widthPixels, ViewUtil.PORTRAIT);
            }
        });
    }

    @Override
    public void onStart() {
        super.onStart();
        mShare.setOnClickListener(v -> {startActivity(new Intent(Intent.ACTION_SEND)
                .putExtra(Intent.EXTRA_TEXT, String.format(mYoutubeUrl, mMedia.overview())));});
        mTrailers.setOnClickListener(v -> mPresenter.loadMovies(mMedia.id()));
        mPresenter.attachView(this);
        mPresenter.loadImages(mMedia.id());
        mPresenter.loadKeywords(mMedia.id());
    }


    @Override
    public void onStop() {
        mPresenter.detachView();
        super.onStop();
    }

    @Override
    public void showImages(String images) {
        ImageView imageView = new ImageView(getContext());
        ViewUtil.loadImage(images, imageView, getContext(), true, true);
        mImageFlipper.addView(imageView, new ViewGroup.LayoutParams(
                ViewGroup.LayoutParams.MATCH_PARENT, ViewGroup.LayoutParams.MATCH_PARENT));
    }

    @Override
    public void showKeywords(List<String> keywords) {
        ((KeywordAdapter) mKeywordRecyclerView.getAdapter()).setKeywords(keywords);
    }

    @Override
    public void showVideos(List<Video> videos) {
        TrailerDialogFragment.newInstance(videos).show(getFragmentManager(), null);
    }

    @Override
    public void showError() {

    }

    private static MediaDetailFragment instantiateWithArguments(Media media) {
        Bundle bundle = new Bundle();
        bundle.putParcelable(RESOURCE, media);
        MediaDetailFragment fragment = new MediaDetailFragment();
        fragment.setArguments(bundle);
        return fragment;
    }

}

我在 onactivitycreated 回调上调用附加监听器。

你能帮我找出丢失的部分吗？

谢谢。

Answer 1

出于某些奇怪的原因，当我将代码包装在可运行对象中时，代码可以正常工作。这是我的解决方案:

@Override
public void onActivityCreated(@Nullable Bundle savedInstanceState) {
    super.onActivityCreated(savedInstanceState);

    final View view = getView();
    if (view == null) return;
    view.getViewTreeObserver().addOnGlobalLayoutListener(() -> {
        view.post(() -> {
            if (mIsTablet) {
                mImageFlipper.getLayoutParams().height =
                        ViewUtil.setHeightForAspectRatio(view.getWidth(), ViewUtil.PORTRAIT);
            } else {
                mImageFlipper.getLayoutParams().height =
                        ViewUtil.setHeightForAspectRatio(mDisplayMetrics.widthPixels, ViewUtil.PORTRAIT);
            }
        });

    });
}

我终于可以解决它，但我不明白为什么。如果你们中有人知道为什么会发生这种情况，请告诉我。