Question

我正在从Web服务加载数据并在ListView中显示它。 ListView项目只有两个视图 - 项目描述的文本和项目图像的图像。数据被下载并传递到AsyncTask中的自定义适配器，该适配器在onCreate方法中执行。除了ImageViews是空的，一切正常。

为了下载图像，我使用在网络上找到的ImageLoader类。它在我下载的示例中工作正常，它只需要两个参数 - 图像网址和图像视图，所以我认为一切都在这里。

我在这里做了一些根本错误的事情吗？

 // Fetch latest items for home screen based on selected city
        private class LatestItems extends AsyncTask<String, Void, String> {

        @Override
        protected String doInBackground(String... loc_id) {

            // For storing data from web service
            String data = "";

            // Downloader object
            UrlDownloader downloader = new UrlDownloader();

            // Building the url to the web service
            String url = "http://www.mywebsite.com/web_services/home_screen_latest_items.php?loc_id="
                    + loc_id[0];

            try {
                // Fetching the data from web service in background
                data = downloader.downloadUrl(url);

            } catch (Exception e) {
                Log.d("Downloader exception", e.toString());
            }
            return data;
        }

        @Override
        protected void onPostExecute(String downloadedData) {
            super.onPostExecute(downloadedData);

            //If web service returned data
            if (downloadedData != null) {
                JSONObject jObject;
                List<HashMap<String, String>> items = null;

                // Instantiate parser
                ItemJSONParser placeJsonParser = new ItemJSONParser();

                try {
                    // Put data into JSON Object and pass it to parser
                    jObject = new JSONObject(downloadedData);
                    items = placeJsonParser.parse(jObject);

                } catch (Exception e) {
                    Log.d("Exception", e.toString());
                }

                // Instantiate adapter. Provide Context, Item layout and
                // DataSource (result)
                ItemPreviewAdapter itemPreview = new ItemPreviewAdapter(
                        getApplicationContext(), R.layout.lvitem_homepage_item,
                        items);

                // Pass each data to from list into to adapter
                for (HashMap<String, String> data : items) {
                    itemPreview.add(data);
                }

                // Set adapter
                latestItemsList.setAdapter(itemPreview);
            }
        }

    }

项目布局：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:background="#fff"
    android:orientation="vertical"
    android:padding="5dp" >

    <ImageView
        android:id="@+id/ivItemImage"
        android:layout_width="75dp"
        android:layout_height="100dp"
        android:scaleType="centerCrop"
        android:src="@drawable/ic_launcher" />

    <TextView
        android:id="@+id/tvItemName"
        android:layout_width="fill_parent"
        android:layout_height="40dp"
        android:gravity="center_horizontal"
        android:lines="2"
        android:textColor="#000"
        android:textSize="10sp" />

</LinearLayout>

自定义适配器：

public class ItemPreviewAdapter extends ArrayAdapter<HashMap<String, String>> {

    private final List<HashMap<String, String>> items;
    private final LayoutInflater mLayoutInflater;

    static class ViewHolder {
        TextView tvIname;
        ImageView image;
    }

    public ItemPreviewAdapter(final Context context,
            final int textViewResourceId, List<HashMap<String, String>> map) {
        super(context, textViewResourceId);
        mLayoutInflater = LayoutInflater.from(context);
        this.items = map;

        Log.i("Adapter", items.toString());
    }

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

        ViewHolder holder;

        if (convertView == null) {
            convertView = mLayoutInflater.inflate(
                    R.layout.lvitem_homepage_item, parent, false);

            holder = new ViewHolder();
            holder.tvIname = (TextView) convertView
                    .findViewById(R.id.tvItemName);
            holder.image = (ImageView) convertView
                    .findViewById(R.id.ivItemImage);

            convertView.setTag(holder);

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

        HashMap<String, String> item = items.get(position);

        String id = item.get("id");
        String item_name = item.get("iname");

        holder.tvIname.setText(item_name);

        String image_url = "http://www.mywebsite.com/images/items/cropped_image_list_id_"
                + id + ".png";

        ImageLoader imgLoader = new ImageLoader(getContext());
        imgLoader.DisplayImage(image_url, holder.image);

        return convertView;
    }
}

Answer 1

将您的图像加载器类声明为全局并在Constructor中初始化。

ImageLoader imgLoader;

 public ItemPreviewAdapter(final Context context,
            final int textViewResourceId, List<HashMap<String, String>> map) {
        super(context, textViewResourceId);
        .....
        .....

       imgLoader = new ImageLoader(context);
    }

还要从getView中删除它真是太棒了......

Answer 2

请使用活动的上下文，而不是使用Adapter类的getContext（）

Context context;


public ItemPreviewAdapter(final Context context,final int textViewResourceId, List<HashMap<String, String>> map) 
{
    super(context, textViewResourceId);
    mLayoutInflater = LayoutInflater.from(context);
    this.items = map;
    this.context=context;

    Log.i("Adapter", items.toString());
}

并使用此上下文在getView方法

中初始化ImageLoader类

ImageLoader imgLoader = new ImageLoader(context);

来自URL的图像未在自定义适配器中加载

2 个答案: