java - ListView 在自定义适配器中重复项目

Question

我正在学习 android，我的代码运行良好。它从网站获取数据并将其显示在列表中。但是当 subcat==1 时，它有 9 个项目需要获取。它显示 7 个不同的项目并重复两个项目。首先它只显示 4 个，即 NullPointerException 第 5 个图像没有名称，因此它重复 4 个图像直到 9 次，但现在一切都很好，它仍然只显示 7 个图像，然后重复 2 个图像。这是我的代码:

public class JSONAsyncTask extends AsyncTask<String, Void, Void> {
    ProgressDialog pd;
    Context context;


    JSONAsyncTask(Context context) {
        this.context = context;
    }

    @Override
    protected void onPreExecute() {

        super.onPreExecute();
        pd = new ProgressDialog(context);
        pd.setIndeterminate(true);
        pd.setCancelable(false);
        pd.setCanceledOnTouchOutside(false);
        pd.setMessage("Please wait..\nLoading data");
        pd.show();
    }

    @Override
    protected Void doInBackground(String... strings) {
        ArrayList<item> jsonArrayList = new ArrayList<item>();
        try {
            HttpClient client = new DefaultHttpClient();
            HttpGet httpget = new HttpGet("http://avdeal.in/get_all_products.php");
            HttpResponse response = client.execute(httpget);
            HttpEntity entity = response.getEntity();
            String data = EntityUtils.toString(entity);
            JSONObject jsonObject = new JSONObject(data);
            if (jsonObject != null) {
                String posts = jsonObject.getString("products");
                JSONArray postsArray = new JSONArray(posts);
                if (postsArray != null) {
                    if (postsArray.length() > 0) {
                        for (int i = 0; i < postsArray.length(); i++) {
                            JSONObject postsObject = postsArray
                                    .getJSONObject(i);
                            int subcat = postsObject.getInt("subcat_id");

                            if (subcats == subcat) {
                                int id=postsObject.getInt("id");
                                String title = postsObject.getString("product_title");
                                String price = postsObject.getString("product_price");
                                String url = "http://avdeal.in/seller/upload_images/" + postsObject.getString("product_url");


                                list1.add(new item(id, title, price, url));
                            }

                        }
                    }


                }
            }
        } catch (Exception e) {
            e.printStackTrace();
            return null;
        }
        return null;
    }

    @Override
    protected void onPostExecute(Void result) {

        super.onPostExecute(result);
        if (list1 != null) {
            pd.dismiss();
            adp = new actorAdapter(context, R.layout.listview, list1);
            lv.setAdapter(adp);
            adp.notifyDataSetChanged();
        }
        else {
            pd.setMessage("No internet access");
        }
        lv.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> adapterView, View view, int i, long l) {
                Toast.makeText(itemView.this, "Please Wait " + i + 1, Toast.LENGTH_SHORT).show();
                int id1 = list1.get(i).getId();
                String name = list1.get(i).getName();
                String price = list1.get(i).getPrice();
                Bitmap bitmap = list1.get(i).getImage();

                if (bitmap == null) {
                    Intent intent = new Intent(context, productDetail.class);
                    intent.putExtra("name", name);
                    intent.putExtra("price", price);
                    intent.putExtra("id", id1);
                    intent.putExtra("imagena", 1);
                    startActivity(intent);
                } else {
                    ByteArrayOutputStream stream = new ByteArrayOutputStream();
                    bitmap.compress(Bitmap.CompressFormat.PNG, 100, stream);
                    byte[] byteArray = stream.toByteArray();
                    Intent intent = new Intent(context, productDetail.class);
                    intent.putExtra("name", name);
                    intent.putExtra("price", price);
                    intent.putExtra("image", byteArray);
                    intent.putExtra("id", id1);
                    startActivity(intent);
                }
            }
        });
    }
}

private class ImageLoadTask extends AsyncTask<String, String, Bitmap>{
            Context context;
        ImageLoadTask(Context context) {
            this.context = context;
        }
        @Override
        protected Bitmap doInBackground(String... strings) {
            for(int i = 0 ; i < list1.size() ; i++)
            {
                if (list1.get(i).getImage()==null);
                {
                    String url=list1.get(i).getUrl();
                    InputStream is = null;
                    try {
                        is = (InputStream) new URL(url).getContent();
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
                    Bitmap b = BitmapFactory.decodeStream(is);
                    list1.set(i, new item(list1.get(i).getId(), list1.get(i).getName(), list1.get(i).getPrice(), list1.get(i).getUrl() ,b));
                }
            }
                return null;

    }

        @Override
        protected void onProgressUpdate(String... values) {
            super.onProgressUpdate(values);

        }
        protected void onPostExecute(Bitmap result){
                super.onPostExecute(result);
                adp = new actorAdapter(context, R.layout.listview, list1);
                lv.setAdapter(adp);
                adp.notifyDataSetChanged();
        }
    }

我可以做些什么来延迟加载图像吗？我尝试创建另一个 AsyncTask，但它在加载所有图像时显示图像。

我可以在下载一张图像后立即更新我的 ListView 吗？

请帮忙。我自己无法弄清楚。这两个问题阻碍了我了解更多。

public View getView(int position, View convertView, ViewGroup parent){
    inflater= (LayoutInflater) context.getSystemService(context.LAYOUT_INFLATER_SERVICE);
    View v =convertView;
    if (v == null) {

        holder=new ViewHolder();
        v=inflater.inflate(Resource,null);
        holder.name= (TextView) v.findViewById(R.id.titles);
        holder.price= (TextView) v.findViewById(R.id.price);
        holder.img= (ImageView) v.findViewById(R.id.itemimage);
        v.setTag(holder);
        holder.name.setText(list1.get(position).getName());
        holder.price.setText((CharSequence) list1.get(position).getPrice());
        holder.img.setImageBitmap(list1.get(position).getImage());



    }
    else {
        holder = (ViewHolder) v.getTag();
    }


    return v;
}

Answer 1

对于延迟图像加载，您需要为每个图像创建一个AsyncTask，而不是为所有图像创建一个AsyncTask(dwonload它们在单独的异步任务)。

我建议您使用这些库之一:

• Universal-Image-Loader

• Picasso

• Glide

• Fresco

这是 4 个库之间基于意见的比较表(来自 here )，它可能会帮助您选择:

编辑:

对于重复的项目，请更改 getView 方法，如下所示:

public View getView(int position, View convertView, ViewGroup parent){
    inflater= (LayoutInflater) context.getSystemService(context.LAYOUT_INFLATER_SERVICE);
    View v =convertView;
    if (v == null) {

        holder=new ViewHolder();
        v=inflater.inflate(Resource,null);
        holder.name= (TextView) v.findViewById(R.id.titles);
        holder.price= (TextView) v.findViewById(R.id.price);
        holder.img= (ImageView) v.findViewById(R.id.itemimage);
        v.setTag(holder);
    }
    else {
        holder = (ViewHolder) v.getTag();
    }

        holder.name.setText(list1.get(position).getName());
        holder.price.setText((CharSequence) list1.get(position).getPrice());
        holder.img.setImageBitmap(list1.get(position).getImage());    

    return v;
}

您在使用回收 View 时忘记更新项目数据 (v != null)。