Question

我一直在搜索SO主题以寻找答案，但无法从之前的讨论中找出我的问题。我有一个listview加载大约50个图像（它曾经是大约100个图像，但根本没有加载任何图像）。从api端点获取我的JSON内容（包括图像URL）后，通过适配器，我的代码将它放在listview中。

目前，有50张图片，当我向下滚动Feed时，毕加索会一次加载一张图片。我觉得好像保持滚动固定在列表视图中的一个项目将使该图像加载更快。然而，当我向上滚动时，它会将占位符重新放入并重新加载图像。有没有办法解决这个问题？

public class MainActivity extends Activity {
    private List<Post> myPosts = new ArrayList<Post>();
    protected String[] mBlogPostTitles;
    public static final String TAG = MainActivity.class.getSimpleName();//prints name of class without package name

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        if(isNetworkAvailable()) {
            GetBlogPostsTask getBlogPostsTask = new GetBlogPostsTask(); // new thread
            getBlogPostsTask.execute();// don't call do in background directly
        }else{
            Toast.makeText(this, "Network is unavailable", Toast.LENGTH_LONG).show();
        }
    }
    public boolean isNetworkAvailable() {
        ConnectivityManager manager = (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);
        NetworkInfo networkInfo = manager.getActiveNetworkInfo();

        boolean isAvailable = false;

        if(networkInfo != null && networkInfo.isConnected()){
            isAvailable = true;
        }

        return isAvailable;
    }
    private void populateListView() {
        ArrayAdapter<Post> adapter = new MyListAdapter();
        ListView list = (ListView) findViewById(R.id.postsListView);
        list.setAdapter(adapter);
    }

    private class MyListAdapter extends ArrayAdapter<Post>{
        public MyListAdapter() {
            super(MainActivity.this, R.layout.item_view, myPosts);
        }

        @Override
        public View getView(int position, View convertView, ViewGroup parent) {

            // make sure we have a view to work with
            View itemView = convertView;
            if (itemView == null) {
                itemView = getLayoutInflater().inflate(R.layout.item_view, parent,false);
            }
            //find the post to work with
            Post currentPost = myPosts.get(position);
            Context context = itemView.getContext();

            String imageURL = currentPost.getImage();
            if(imageURL == null || imageURL.isEmpty()){
                ImageView imageView = (ImageView) itemView.findViewById(R.id.item_image);
                imageView.setVisibility(View.GONE);
            }else{
                ImageView imageView = (ImageView) itemView.findViewById(R.id.item_image);
                Picasso.with(context)
                        .load(imageURL)
                        .tag(context)
                        .placeholder(R.drawable.kanye8080s)
                        .error(R.drawable.stadiumarcadium)
                        .into(imageView);
                imageView.setVisibility(View.VISIBLE);
            }

            //Username
            TextView userText = (TextView) itemView.findViewById(R.id.item_txtUser);
            userText.setText(currentPost.getUser());

            //Time of post
            TextView timeText = (TextView) itemView.findViewById(R.id.item_txtTime);
            timeText.setText("" + currentPost.getTime());

            //The actual post
            TextView postText = (TextView) itemView.findViewById(R.id.item_txtPost);
            postText.setText("" + currentPost.getPost());

            //The actual post
            TextView likesText = (TextView) itemView.findViewById(R.id.item_txtLikes);
            likesText.setText("" + currentPost.getLikes());

            return itemView;
        }
    }

    private class GetBlogPostsTask extends AsyncTask<Object, Void, List> {

        @Override
        protected List doInBackground(Object[] params) {

            int responseCode = -1;//need to have this variable outside scope of try/catch block
            JSONObject jsonResponse = null;
            StringBuilder builder = new StringBuilder();
            HttpClient client = new DefaultHttpClient();
            HttpGet httpget = new HttpGet(""); /// api endpoint redacted

            try {

                HttpResponse response = client.execute(httpget);
                StatusLine statusLine = response.getStatusLine();
                responseCode = statusLine.getStatusCode();

                if(responseCode == HttpURLConnection.HTTP_OK){ //could have used just 200 value
                    HttpEntity entity = response.getEntity();
                    InputStream content = entity.getContent();
                    BufferedReader reader = new BufferedReader(new InputStreamReader(content));
                    String line;
                    while((line = reader.readLine()) != null){
                        builder.append(line);
                    }

                    jsonResponse = new JSONObject(builder.toString());

                    JSONArray jsonPosts = jsonResponse.getJSONArray("posts");
                    for(int i=0; i < jsonPosts.length(); i++ ){
                        JSONObject jsonPost = jsonPosts.getJSONObject(i);

                        int post_id = Integer.parseInt(jsonPost.getString("id"));
                        String post_user = jsonPost.getString("user");
                        String post_account = jsonPost.getString("account");
                        int post_time = Integer.parseInt(jsonPost.getString("time"));
                        String post_post = jsonPost.getString("post");
                        String post_image = jsonPost.getString("image");
                        int post_likes = Integer.parseInt(jsonPost.getString("likes"));

                        myPosts.add(new Post(post_id, post_user, post_account, post_time, post_post, post_image, "profile picture here", post_likes));
                    }
                }else{
                    Log.i(TAG, "Unsuccessful HTTP Response Code: " + responseCode);
                }
            }
            catch (MalformedURLException e){
                Log.e(TAG, "Exception caught");
            }
            catch (IOException e){
                Log.e(TAG, "Exception caught");
            }
            catch (Exception e){//must be in this order, this is the last, general catch
                Log.e(TAG, "Exception caught", e);
            }

            return null;
        }
        @Override
        protected void onPostExecute(List result) {
            // call populateListView method here
            populateListView();
            super.onPostExecute(result);
        }
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.menu_main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }
}

任何帮助将不胜感激，

谢谢！

修改

大家好，

我已将我的代码更新为视图持有者模式，创建了两个单独的视图（一个用于带有图像的帖子，一个用于带有文本的帖子），还包括Picasso的新scroll detection capabilities。

我已经看到一些图像的加载速度更快，至少在滚动时聚焦视图时，图像现在更有可能加载。然而，在向上滚动那些曾经加载过的相同图像时，它们会消失。感觉好像毕加索一次只加载4-5张图像并替换已装载的图像以腾出空间。我的更新代码如下：

public class MainActivity extends Activity {
    private List<Post> myPosts = new ArrayList<Post>();
    protected String[] mBlogPostTitles;
    public static final String TAG = MainActivity.class.getSimpleName();//prints name of class without package name

    ...

    private void populateListView() {
        Activity activity = MainActivity.this;

        ArrayAdapter<Post> adapter = new MyListAdapter();
        ListView list = (ListView) findViewById(R.id.postsListView);
        list.setAdapter(adapter);
        list.setOnScrollListener(new SampleScrollListener(activity));
    }

    private class MyListAdapter extends ArrayAdapter<Post>{
        public MyListAdapter() {
            super(MainActivity.this, R.layout.item_view, myPosts);
        }

        @Override
        public int getViewTypeCount() {
            return 2;
        }

        @Override
        public int getItemViewType(int position) {
            String imageURL = myPosts.get(position).getImage();
            if(imageURL == null || imageURL.isEmpty()){
                return 1; // text based
            }else{
                return 0; // image based
            }
        }

        @Override
        public View getView(int position, View convertView, ViewGroup parent) {

            PostViewHolder holder;

            int type = getItemViewType(position);

            View itemView = convertView;

            // make sure we have a view to work with
            if (itemView == null) {
                holder = new PostViewHolder();
                if(type == 1) {
                    itemView = getLayoutInflater().inflate(R.layout.item_view, parent, false);
                }else {
                    itemView = getLayoutInflater().inflate(R.layout.image_post_view, parent, false);
                    holder.image = (ImageView) itemView.findViewById(R.id.item_image);
                }
                holder.user = (TextView) itemView.findViewById(R.id.item_txtUser);
                holder.time = (TextView) itemView.findViewById(R.id.item_txtTime);
                holder.post = (TextView) itemView.findViewById(R.id.item_txtPost);
                holder.likes = (TextView) itemView.findViewById(R.id.item_txtLikes);

                itemView.setTag(holder);
            } else {
                holder = (PostViewHolder) itemView.getTag();
            }

            //find the post to work with
            Post currentPost = myPosts.get(position);

            if(type != 1) {
                Context context = itemView.getContext();
                String imageURL = currentPost.getImage();

                Picasso.with(context).setIndicatorsEnabled(true);
                //Picasso.with(context).setLoggingEnabled(true);
                Picasso.with(context)
                        .load(imageURL)
                        .tag(context)
                        .placeholder(R.drawable.kanye8080s)
                        //.skipMemoryCache()
                        .error(R.drawable.stadiumarcadium)
                        .fit()
                        .into(holder.image);
            }
            //Username
            holder.user.setText(currentPost.getUser());

            //Time of post
            holder.time.setText("" + currentPost.getTime());

            //The actual post
            holder.post.setText(currentPost.getPost());

            //Likes for the post
            holder.likes.setText("" + currentPost.getLikes());

            return itemView;
        }
    }
    public class SampleScrollListener implements AbsListView.OnScrollListener {
        private final Context context;

        public SampleScrollListener(Context context) {
            this.context = context;
        }

        @Override
        public void onScrollStateChanged(AbsListView view, int scrollState) {
            final Picasso picasso = Picasso.with(context);
            if (scrollState == SCROLL_STATE_IDLE || scrollState == SCROLL_STATE_TOUCH_SCROLL) {
                picasso.resumeTag(context);
            } else {
                picasso.pauseTag(context);
            }
        }

        @Override
        public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount,
                             int totalItemCount) {
            // Do nothing.
        }
    }


    ...
}

问题来自哪里？我应该在缓存中以某种方式预加载这些图像吗？虽然我已经研究过毕加索的新优先功能，但我应该告诉Picasso以某种方式按照它们在我的列表视图中出现的顺序加载图像吗？有任何想法吗？我怎样才能保持＆＃34;已经加载的图像向上滚动？谢谢！

- 24x7

Answer 1

使用picasso调整大小

 Picasso.with(context)
.load(imageURL)
.tag(context)
.placeholder(R.drawable.kanye8080s)
.error(R.drawable.stadiumarcadium)
.into(imageView)
.resize(x,y);

//这肯定有帮助

Answer 2

Picasso的内存缓存大小有限，因此在滚动长列表时不会产生内存不足错误。一旦图像超出内存缓存，将在从磁盘缓存或网络重新加载映像时显示占位符。

默认情况下启用磁盘缓存，因此重新加载时间应该非常快。您可以使用setIndicatorsEnabled(true)查看图像的加载位置。

如果您发现Picasso正在从网络重新加载图像，这可能是从服务器发送的HTTP标头的问题。我不相信Picasso实际上会将图像缓存在磁盘本身上，而是依赖于HTTP层，它将服从无缓存头，并且如果过期时间过去将从网络重新加载。

Answer 3

我要看两件事。

第一个是正在加载的图像的大小。我不知道Picasso中默认的最大缓存大小是多少，但听起来你只需要几张图片就可以超出它，导致其他图像从缓存中逐出。

第二个可能不是核心问题，但也有助于提高绩效。你正在做很多findViewById（）调用，它们相当昂贵。查看＆＃34; ViewHolder＆＃34;模式＆＃34;缓存＆＃34;那些查找。

修改 - 有关详细信息，请参阅Jake Wharton's answer to a similar question

Answer 4

我建议您使用GLIDE进行图像加载。由于GLIDE快速且具有缓存加载功能，因此您可以获得超快的图像加载，使用GLIDE可以获得很多功能。

在此下载 https://github.com/bumptech/glide

Answer 5

使用：

recyclerview.getRecycledViewPool().setMaxRecycledViews(0, 0);

这解决了我的问题

Picasso在listview中向上滚动时不断重新加载图像，加载缓慢

5 个答案: