java - 更新 RecycleView 中的 CardView 项目时遇到延迟

Question

我在使用 CardViews 时遇到问题。我创建了一个包含 1 个 TextView 和 2 个 ImageView 的 CardView ，它显示在 RecycleView 中。当我尝试更新其中一张 CardView 的内容(创建了 5 张用于测试的卡片)时，滚动更新的卡片时界面开始滞后，但当我传递该项目时又恢复正常。仅当存在 ImageView 时才会发生这种情况，当用 ImageView 替换其中包含一些随机文本的 TextView 时，它可以正常工作。

现在，这是我的代码，之后我将添加一些可能导致此问题的更多信息。

首先是 Adapter 类，它还包含 items 类和 List :

public class MovieDetailsAdapter extends RecyclerView.Adapter<MovieDetailsAdapter.MovieViewHolder> {

public List<MovieDetails> movieList;
private static final String TAG = "MyAdapter";

public MovieDetailsAdapter() {

    movieList = new ArrayList< MovieDetails>();
}




public void setItemCount(int count ,String title, Bitmap poster,Bitmap fanart ) {
    movieList.clear();
    movieList.addAll(generateDummyData(count, title, poster , fanart));

    notifyDataSetChanged();
}


@Override
public int getItemCount() {

    return movieList.size();
}


public void addItem(int position,String title, Bitmap poster, Bitmap fanart) {
   if (position > movieList.size()) return;

    movieList.add(position, generateDummyItem(title, poster, fanart));
   // notifyDataSetChanged();
    notifyItemInserted(position);
}

public void updateItem(int position, String title, Bitmap poster, Bitmap fanart) {
    if (position > movieList.size()) return;

    movieList.add(position, generateDummyItem(title, poster, fanart));
     notifyItemChanged(position);
  //  notifyDataSetChanged();
}


@Override
public MovieViewHolder onCreateViewHolder(ViewGroup viewGroup, int i) {
    View itemView = LayoutInflater.
            from(viewGroup.getContext()).
            inflate(R.layout.card_layout_movies, viewGroup, false);
    Log.d(TAG, "create header view holder");
    return new MovieViewHolder(itemView);
}

@Override
public void onBindViewHolder(MovieViewHolder movieViewHolder, int i) {

    Log.d(TAG, "bind header view holder");
    MovieDetails mdet = movieList.get(i);

    movieViewHolder.vTitle.setText(mdet.Title);
    movieViewHolder.vPoster.setImageBitmap(mdet.imageViewPoster);
    movieViewHolder.vFanart.setImageBitmap(mdet.imageViewFanart);

    Log.d(TAG, "position: " + i + " holder: " + movieViewHolder + " text: " + movieViewHolder.vTitle);


}


public static class MovieViewHolder extends RecyclerView.ViewHolder {

    protected TextView vTitle;
    protected ImageView vPoster;
    protected ImageView vFanart;

    public MovieViewHolder(View v)
    {
        super(v);
        vTitle  = (TextView)  v.findViewById(R.id.title);
        vPoster = (ImageView) v.findViewById(R.id.imageViewPoster);
        vFanart = (ImageView) v.findViewById(R.id.imageViewFanart);

    }

}


public static class MovieDetails {

    protected String title;
    protected Bitmap imageViewPoster;
    protected Bitmap imageViewFanart;

    public MovieDetails(String title, Bitmap imageViewPoster,Bitmap imageViewFanart )
    {
        this.title = title;
        this.imageViewPoster = imageViewPoster;
        this.imageViewFanart = imageViewFanart;
    }
}

public static MovieDetails generateDummyItem(String title, Bitmap poster, Bitmap fanart) {

    MovieDetails mov = new MovieDetails(title, poster, fanart);
    return  mov;
}

public static List< MovieDetailsAdapter.MovieDetails> generateDummyData(int count, String title , Bitmap imageViewPoster, Bitmap imageviewFanart) {


    ArrayList<MovieDetailsAdapter.MovieDetails> items = new ArrayList<MovieDetailsAdapter.MovieDetails>();

    for (int i=0; i < count; i++) {

        items.add(new MovieDetailsAdapter.MovieDetails(title, imageViewPoster, imageviewFanart));
    }

    return items;
}

}

现在，这是我的主类， Activity 类

public class MoviesListActivity extends AppCompatActivity {

public MovieDetailsAdapter ca = new MovieDetailsAdapter();
public RecyclerView recList;
private Button button;



@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_movies_list);
    RecyclerView recList = (RecyclerView) findViewById(R.id.cardList);

    LinearLayoutManager llm = new LinearLayoutManager(this);
    llm.setOrientation(LinearLayoutManager.VERTICAL);
    recList.setLayoutManager(llm);
    button = (Button) findViewById(R.id.button);
    MyOnClickListener Listener = new MyOnClickListener();
    button.setOnClickListener(Listener);

    recList.setItemAnimator(null);

    Bitmap bittest1 = decodeSampledBitmapFromResource(getResources(), R.drawable.poster_example, 640, 955);
    Bitmap bittest2 = decodeSampledBitmapFromResource(getResources(), R.drawable.fanart_example, 800, 450);

    ca.setItemCount(5, "TestingTitle", bittest1, bittest2);
    recList.setAdapter(ca);
}



public class MyOnClickListener implements View.OnClickListener {

    @Override
    public void onClick(View v) {
        switch (v.getId()) {
            case R.id.button:

                Bitmap bittest12 = decodeSampledBitmapFromResource(getResources(), R.drawable.poster2, 640, 955);
                Bitmap bittest22 = decodeSampledBitmapFromResource(getResources(), R.drawable.fanart2, 800, 450);

                Toast.makeText(getApplicationContext(), "msg msg", Toast.LENGTH_SHORT).show();

                ca.updateItem(1, "test", bittest12, bittest22);
               // ca.addItem(1,"test",bittest12,bittest22);
                break;
            default:
                break;
        }
    }
}

//------methods used for resizing the images down to smaller ones before loading into memory---//


public static Bitmap decodeSampledBitmapFromResource(Resources res, int resId,
                                                        int reqWidth, int reqHeight) {

    // First decode with inJustDecodeBounds=true to check dimensions
    final BitmapFactory.Options options = new BitmapFactory.Options();
    options.inJustDecodeBounds = true;
    BitmapFactory.decodeResource(res, resId, options);

    // Calculate inSampleSize
    options.inSampleSize = calculateInSampleSize(options, reqWidth, reqHeight);

    // Decode bitmap with inSampleSize set
    options.inJustDecodeBounds = false;
    return BitmapFactory.decodeResource(res, resId, options);
}

public static int calculateInSampleSize(
        BitmapFactory.Options options, int reqWidth, int reqHeight) {
    // Raw height and width of image
    final int height = options.outHeight;
    final int width = options.outWidth;
    int inSampleSize = 1;

    if (height > reqHeight || width > reqWidth) {

        final int halfHeight = height / 2;
        final int halfWidth = width / 2;

        // Calculate the largest inSampleSize value that is a power of 2 and keeps both
        // height and width larger than the requested height and width.
        while ((halfHeight / inSampleSize) > reqHeight
                && (halfWidth / inSampleSize) > reqWidth) {
            inSampleSize *= 2;
        }
    }

    return inSampleSize;
  }

最后，我的 CardView XML 可能并不重要。

<android.support.v7.widget.CardView
xmlns:card_view="http://schemas.android.com/apk/res-auto"
xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/card_view"
android:layout_width="match_parent"
android:layout_height="match_parent"
card_view:cardCornerRadius="4dp"
android:layout_margin="5dp">


<RelativeLayout
    android:layout_width="match_parent"
    android:layout_height="match_parent">
    <TextView
        android:id="@+id/title"
        android:layout_width="match_parent"
        android:layout_height="20dp"
        android:background="@color/bkg_card"
        android:text="Movie Title"
        android:gravity="center_vertical"
        android:textColor="@android:color/white"
        android:textSize="14dp"/>

    <ImageView
        android:elevation="5dp"
        android:scaleType="fitCenter"
        android:layout_width="100dp"
        android:layout_height="150dp"
        android:id="@+id/imageViewPoster"
        android:text="Poster"
        android:gravity="center_vertical"
        android:layout_below="@id/title"
        android:layout_marginTop="10dp"
        android:layout_marginLeft="5dp"/>

    <ImageView
        android:id="@+id/imageViewFanart"
        android:scaleType="fitCenter"
        android:layout_alignBottom="@+id/imageViewPoster"
        android:layout_toEndOf="@+id/imageViewPoster"
        android:layout_width= "235dp"
        android:layout_height="122dp"
        android:layout_marginRight="5dp"/>


</RelativeLayout>

现在，另一个讨论中的某人向我展示了这是一个可能的原因:Why RecyclerView.notifyItemChanged() will create a new ViewHolder and use both the old ViewHolder and new one?

所以我在适配器的 onBind 和 onCreate 方法中添加了 Log 项，看看这是否会导致它，事实上，它不仅仅是创建一个额外的 ViewHolders，而是创建其中的 3 个，每次我滚动新更新的卡片时，它似乎都会重新绑定(bind)，onBind 方法似乎每次都会被调用。

根据线程中的解决方案将动画设置为“null”在我的情况下似乎没有任何效果，所以也许这不是导致它的原因。

有什么想法吗？

Answer 1

嗯，我解决了。似乎只有当我通过 XML 方法加载图像时才会发生这种情况，如果我使用像 Picasso 这样的第三方库加载它们，那么延迟似乎就会消失。像这样的东西:

Picasso.with(context).load(MovieDetails.getPoster())
            .error(R.drawable.placeholder)
            .placeholder(R.drawable.placeholder)
            .into(movieViewHolder.imageViewPoster);

在onBindViewHolder里面无需传递位图，只需传递一个字符串作为图像的 URL 或位置。并将 Context 传递给 Adapter 类。