Question

我是新的Android现在我想从网址显示图像。我在listview中使用imageview。我想将图像列表添加到列表项的每一行。我使用了SimpleAdapter，但是imageview显示为空白。

以下是主要活动：

package com.example.mysqltest;

    import java.util.ArrayList;
    import java.util.HashMap;
    import org.json.JSONArray;
    import org.json.JSONException;
    import org.json.JSONObject;
    import android.app.ListActivity;
    import android.app.ProgressDialog;
    import android.content.Intent;
    import android.os.AsyncTask;
    import android.os.Bundle;
    import android.view.View;
    import android.widget.AdapterView;
    import android.widget.AdapterView.OnItemClickListener;
    import android.widget.ListAdapter;
    import android.widget.ListView;
    import android.widget.SimpleAdapter;

    public class ReadComments extends ListActivity {

        // Progress Dialog
        private ProgressDialog pDialog;

        // testing on Emulator:
        private static final String READ_COMMENTS_URL = "http://192.168.30.198/test/webservice/comments.php";


        // JSON IDS:
        private static final String TAG_SUCCESS = "success";
        private static final String TAG_TITLE = "title";
        private static final String TAG_POSTS = "posts";
        private static final String TAG_POST_ID = "post_id";
        private static final String TAG_USERNAME = "username";
        private static final String TAG_MESSAGE = "message";
        private static final String TAG_IMAGE = "image";


        // An array of all of our comments
        private JSONArray mComments = null;
        // manages all of our comments in a list.
        private ArrayList<HashMap<String, String>> mCommentList;

        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            // note that use read_comments.xml instead of our single_post.xml
            setContentView(R.layout.read_comments);
        }

        @Override
        protected void onResume() {
            // TODO Auto-generated method stub
            super.onResume();
            // loading the comments via AsyncTask
            new LoadComments().execute();
        }

        public void addComment(View v) {
            Intent i = new Intent(ReadComments.this, AddComment.class);
            startActivity(i);
        }

        /**
         * Retrieves recent post data from the server.
         */
        public void updateJSONdata() {
            mCommentList = new ArrayList<HashMap<String, String>>();

            JSONParser jParser = new JSONParser();      
            JSONObject json = jParser.getJSONFromUrl(READ_COMMENTS_URL);

            try {
                mComments = json.getJSONArray(TAG_POSTS);

                for (int i = 0; i < mComments.length(); i++) {
                    JSONObject c = mComments.getJSONObject(i);

                    // gets the content of each tag
                    String title = c.getString(TAG_TITLE);
                    String content = c.getString(TAG_MESSAGE);
                    String username = c.getString(TAG_USERNAME);
                    String image = c.getString(TAG_IMAGE);

                    // creating new HashMap
                    HashMap<String, String> map = new HashMap<String, String>();

                    map.put(TAG_TITLE, title);
                    map.put(TAG_MESSAGE, content);
                    map.put(TAG_USERNAME, username);
                    map.put(TAG_IMAGE, image);

                    // adding HashList to ArrayList
                    mCommentList.add(map);
                }

            } catch (JSONException e) {
                e.printStackTrace();
            }
        }

        /**
         * Inserts the parsed data into the listview.
         */
        private void updateList() { 
            ListAdapter adapter = new SimpleAdapter(this, mCommentList,
                    R.layout.single_post, new String[] { TAG_TITLE, TAG_MESSAGE,
                            TAG_USERNAME,TAG_IMAGE }, new int[] { R.id.title, R.id.message,
                            R.id.username, R.id.imageView1 });

            // I shouldn't have to comment on this one:
            setListAdapter(adapter);    

            ListView lv = getListView();    
            lv.setOnItemClickListener(new OnItemClickListener() {

                @Override
                public void onItemClick(AdapterView<?> parent, View view,
                        int position, long id) {}
            });
        }

        public class LoadComments extends AsyncTask<Void, Void, Boolean> {

            @Override
            protected void onPreExecute() {
                super.onPreExecute();
                pDialog = new ProgressDialog(ReadComments.this);
                pDialog.setMessage("Loading Comments...");
                pDialog.setIndeterminate(false);
                pDialog.setCancelable(true);
                pDialog.show();
            }

            @Override
            protected Boolean doInBackground(Void... arg0) {
                updateJSONdata();
                return null;

            }

            @Override
            protected void onPostExecute(Boolean result) {
                super.onPostExecute(result);
                pDialog.dismiss();
                updateList();
            }
        }
    }

Answer 1

好。所以我在这里假设您坚持使用SimpleAdapter。没有问题，问题解决了，只需按照以下步骤操作：

首先，我们为ListView创建自定义 row.xml ，其中只包含一个ImageView。（您可以稍后添加您喜欢的内容但现在添加我假设您只想加载ImageView）

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:orientation="vertical" >

    <ImageView
        android:id="@+id/imageView1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentLeft="true"
        android:layout_alignParentTop="true"
        android:layout_marginLeft="5dp"
        android:layout_marginTop="5dp"
        android:src="@drawable/ic_launcher" />


</RelativeLayout>

其次，我们可以创建自定义 SimpleAdapter

package com.example.helpstack;

import java.util.HashMap;
import java.util.List;
import java.util.Map;

import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;
import android.widget.SimpleAdapter;

public class MySimpleAdapter extends SimpleAdapter {
    private Context mContext;
    public LayoutInflater inflater = null;

    public MySimpleAdapter(Context context,
            List<? extends Map<String, ?>> data, int resource, String[] from,
            int[] to) {
        super(context, data, resource, from, to);
        mContext = context;
        inflater = (LayoutInflater) mContext
                .getSystemService(Context.LAYOUT_INFLATER_SERVICE);
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        View vi = convertView;
        if (convertView == null)
            vi = inflater.inflate(R.layout.row, null);

        HashMap<String, Object> data = (HashMap<String, Object>) getItem(position);

        new DownloadTask((ImageView) vi.findViewById(R.id.imageView1))
                .execute((String) data.get("uri"));

        return vi;
    }

}

第三个让我们创建我们的DownloadTask，这个类将下载图像：

package com.example.helpstack;

import java.io.IOException;
import java.net.MalformedURLException;
import java.net.URL;

import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.AsyncTask;
import android.widget.ImageView;

public class DownloadTask extends AsyncTask<String, Void, Boolean> {
    ImageView v;
    String url;
    Bitmap bm;

    public DownloadTask(ImageView v) {
        this.v = v;
    }

    @Override
    protected Boolean doInBackground(String... params) {
        url = params[0];
        bm = loadBitmap(url);
        return true;
    }

    @Override
    protected void onPostExecute(Boolean result) {
        // TODO Auto-generated method stub
        super.onPostExecute(result);
        v.setImageBitmap(bm);
    }

    public static Bitmap loadBitmap(String url) {
        try {
            URL newurl = new URL(url);
            Bitmap b = BitmapFactory.decodeStream(newurl.openConnection()
                    .getInputStream());
            return b;
        } catch (MalformedURLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        return null;
    }
}

现在从DownloadTask

中的getView（）内部使用SimpleAdapter

让我们从 MainActivity.java

中运行我们惊人的小项目

package com.example.helpstack;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import android.app.Activity;
import android.os.Bundle;
import android.widget.ListView;

public class MainActivity extends Activity {
    ListView lv;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        lv = (ListView) findViewById(R.id.listView1);
        List<Map<String, Object>> data = new ArrayList<Map<String, Object>>();
        Map<String, Object> map = new HashMap<String, Object>();
        map.put("uri",
                "http://upload.wikimedia.org/wikipedia/commons/thumb/f/f9/Wiktionary_small.svg/350px-Wiktionary_small.svg.png");
        //here u can add as many uri as u want
        data.add(map);
        MySimpleAdapter adapter = new MySimpleAdapter(MainActivity.this, data,
                R.layout.row, new String[] {}, new int[] {});
        lv.setAdapter(adapter);
    }
}

Answer 2

您可以使用任何图像缓存库。例如，Picasa，Universal Image Loader ..

您可以缓存网址中的图片，然后就可以使用应用中的图片了。

您可以在以下链接中找到这些库

http://square.github.io/picasso/和https://github.com/nostra13/Android-Universal-Image-Loader

Answer 3

您可以使用多个线程下载和解码位图。请关注此网站，并尝试了解android Developer如何使用线程池执行器在线程中执行不同的图像。 http://developer.android.com/training/multiple-threads/create-threadpool.html

Answer 4

1）要将图像Uri设置为ImageView，您可以使用ViewBinder
您必须实现抽象类并覆盖setViewValue

2）您可以使用Picasso在后台线程中加载图像并缓存它们。 setViewValue方法如下所示：

boolean setViewValue (View view, Object data, String textRepresentation) {
  if(view.getId() == R.id.imageView1) {
    Picasso.with(view.getContext()).load(textRepresentation).into((ImageView) view);
    return true;
  }
  return false;
}

如果要处理绑定，则返回true。您返回false作为默认行为。

3）通过调用adapter

设置ViewBinder以使用adapter.setViewBinder(ViewBinder);

Answer 5

现在，我的建议是：
1.从网址下载图像 2.将其保存为可存放在存储器中 3.将此drawable设置为imageview的图像src （我没有看到你从你的代码中完成这部分工作......）

Answer 6

本教程是使用json解析解析图像并在列表视图中显示它的最佳示例：http://www.androidbegin.com/tutorial/android-json-parse-images-and-texts-tutorial/

其他一些：

http://imagelistviewdynamic.blogspot.in/2012/12/image-parsed-from-json-using-async-into.html

http://www.java2s.com/Open-Source/Android_Free_Code/JSON/Download_Free_code_Android_JSON_Parse_Images_and_Texts_Tutorial.htm

Answer 7

我建议您使用Universal Image Loader，它使用异步图像下载，缓存和显示，在那里您可以找到如何实现它的示例。在你这样做之后，你不必担心图像的数量或它的大小。

如果您下载项目，您会发现这个示例可以完成您想要的所有工作：

/**
 * @author Sergey Tarasevich (nostra13[at]gmail[dot]com)
 */
public class ImageListActivity extends AbsListViewBaseActivity {

    DisplayImageOptions options;

    String[] imageUrls;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.ac_image_list);

            // here you get a String array with images URL
        Bundle bundle = getIntent().getExtras();
        imageUrls = bundle.getStringArray(Extra.IMAGES);

        options = new DisplayImageOptions.Builder()
            .showImageOnLoading(R.drawable.ic_stub)
            .showImageForEmptyUri(R.drawable.ic_empty)
            .showImageOnFail(R.drawable.ic_error)
            .cacheInMemory(true)
            .cacheOnDisc(true)
            .considerExifParams(true)
            .displayer(new RoundedBitmapDisplayer(20))
            .build();

        listView = (ListView) findViewById(android.R.id.list);
        ((ListView) listView).setAdapter(new ItemAdapter());
        listView.setOnItemClickListener(new OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
                startImagePagerActivity(position);
            }
        });
    }

    @Override
    public void onBackPressed() {
        AnimateFirstDisplayListener.displayedImages.clear();
        super.onBackPressed();
    }
    // it gets the position of listView and opens that image in a new Activity
    private void startImagePagerActivity(int position) {
        Intent intent = new Intent(this, ImagePagerActivity.class);
        intent.putExtra(Extra.IMAGES, imageUrls);
        intent.putExtra(Extra.IMAGE_POSITION, position);
        startActivity(intent);
    }

    class ItemAdapter extends BaseAdapter {

        private ImageLoadingListener animateFirstListener = new AnimateFirstDisplayListener();

        private class ViewHolder {
            public TextView text;
            public ImageView image;
        }

        @Override
        public int getCount() {
            return imageUrls.length;
        }

        @Override
        public Object getItem(int position) {
            return position;
        }

        @Override
        public long getItemId(int position) {
            return position;
        }

        @Override
        public View getView(final int position, View convertView, ViewGroup parent) {
            View view = convertView;
            final ViewHolder holder;
            if (convertView == null) {
                view = getLayoutInflater().inflate(R.layout.item_list_image, parent, false);
                holder = new ViewHolder();
                holder.text = (TextView) view.findViewById(R.id.text);
                holder.image = (ImageView) view.findViewById(R.id.image);
                view.setTag(holder);
            } else {
                holder = (ViewHolder) view.getTag();
            }

            holder.text.setText("Item " + (position + 1));
                    // here is the place where is loaded the image using Universal ImageLoader , imageUrls[position] is a list of images URL
            imageLoader.displayImage(imageUrls[position], holder.image, options, animateFirstListener);

            return view;
        }
    }

    private static class AnimateFirstDisplayListener extends SimpleImageLoadingListener {

        static final List<String> displayedImages = Collections.synchronizedList(new LinkedList<String>());

        @Override
        public void onLoadingComplete(String imageUri, View view, Bitmap loadedImage) {
            if (loadedImage != null) {
                ImageView imageView = (ImageView) view;
                boolean firstDisplay = !displayedImages.contains(imageUri);
                if (firstDisplay) {
                    FadeInBitmapDisplayer.animate(imageView, 500);
                    displayedImages.add(imageUri);
                }
            }
        }
    }
}

Android：通过SimpleAdapter在imageview中显示图像

7 个答案:

http://square.github.io/picasso/和https://github.com/nostra13/Android-Universal-Image-Loader