使用回调异步加载listview中的图像

Question

我在我的应用程序中使用Parse，为了加载我的'profile'图像，我需要检索一个所谓的Parsefile。当下载Parsefile时，它使用回调来通知它何时完成。现在这通常是一种很好的方法，但是当我使用Listview并使用Asynctask下载图像时遇到了这个问题。

问题如下：

在getView方法的ListView适配器中，我创建了一个AsyncTask并执行它，这个AsyncTask启动了retrieveProfileImage(callBack)函数。在我的回调中，我只是在UI线程上启动一个Runnable，用新的（检索到的图像）更新View中的ImageView。但是看起来问题是，只要我启动AsyncTask，就会返回View。所以我无法将其他图像设置为正确的行。我希望我的代码能更清楚地证明我的问题。

ListAdapter：

public class FriendListAdapter extends ArrayAdapter<Profile> {

private int resource;
private Context context;
private List<Profile> friends;
private Profile fProfile;
private Bitmap profileImageBitmap;
private ProgressBar friendImageProgressBar;


//ui
private ImageView friendImage;

public FriendListAdapter(Context context, int resource,
        List<Profile> objects) {
    super(context, resource, objects);
    this.context = context;
    this.resource = resource;
    this.friends = objects;
}



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

    TextView  friendName = null;
    friendImage = null;
    View rowView = convertView;
    if (rowView == null) {
      LayoutInflater inflater = ((Activity) context).getLayoutInflater();
      rowView = inflater.inflate(R.layout.friendslist_row, null);
      friendName = (TextView) rowView.findViewById(R.id.fName);
      friendImage = (ImageView) rowView
          .findViewById(R.id.fImage);
      friendImageProgressBar = (ProgressBar) rowView.findViewById(R.id.friendImageProgressBar);
    } else {
        friendName = (TextView) convertView.findViewById(R.id.fName);
        friendImage = (ImageView) convertView.findViewById(R.id.fImage);
        friendImageProgressBar = (ProgressBar) convertView.findViewById(R.id.friendImageProgressBar);
    }

    fProfile = friends.get(position);

    DownloadProfileImage dImg = new DownloadProfileImage();
    dImg.execute();

    friendName.setText(fProfile.getName());

    return rowView;

}

private class DownloadProfileImage extends AsyncTask<Void, Integer, String> {

    @Override
    protected String doInBackground(Void... arg0) {
        Log.d("logpp", "Starting download image for " + fProfile.getName());
        fProfile.retrieveProfileImage(new ProfileImageCallback());
        return null;
    }

}

private class ProfileImageCallback extends GetDataCallback {

    @Override
    public void done(byte[] bytearray, ParseException e) {
        if (e == null) {
            Log.d("logpp", "Done downloading image for " + fProfile.getName() + ". Setting bitmap to:" +
         " " + friendImage.getId());
            profileImageBitmap = BitmapManager
                    .getBitmapFromByteArray(bytearray);
            ((Activity) context).runOnUiThread(new UpdateUi());
        }
    }
}

private class UpdateUi implements Runnable {

    @Override
    public void run() {
        friendImage.setImageBitmap(profileImageBitmap);
        friendImage.setVisibility(View.VISIBLE);
        friendImageProgressBar.setVisibility(View.INVISIBLE);
    }

}

}

retrieveProfileImage方法：

public void retrieveProfileImage(GetDataCallback callBack) {
    this.image.getDataInBackground(callBack);
}

我希望有人可以帮我这个。

此致

添

Answer 1

我通过以下代码解决了这个问题

public View getView(int position, View convertView, ViewGroup parent) {
    try {
        if (inflater == null)
            inflater = (LayoutInflater) activity.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        if (convertView == null)
            convertView = inflater.inflate(R.layout.answer_item, null);

        TextView name = (TextView) convertView.findViewById(R.id.textView_ans_user_name);
        TextView body = (TextView) convertView.findViewById(R.id.textView_ans_user_body);
        TextView timestamp = (TextView) convertView.findViewById(R.id.textView_ans_user_timestamp);
        final CircularImageView thumbnail = (CircularImageView) convertView.findViewById(R.id.imageView_ans_user);
        Parse_answer_model ans = answers.get(position);
        name.setText(ans.getAns_by());
        body.setText(ans.getAns_body());
        SimpleDateFormat sdfAmerica = new SimpleDateFormat("dd-M-yyyy hh:mm:ss a");
        sdfAmerica.setTimeZone(TimeZone.getDefault());
        String sDateInAmerica = sdfAmerica.format(ans.getCreatedAt());
        timestamp.setText(sDateInAmerica);
        ParseQuery<User> query = ParseQuery.getQuery("_User");
        query.whereEqualTo("username", ans.getAns_by());
        query.getFirstInBackground(new GetCallback<User>() {

            public void done(User user, ParseException e) {
                // TODO Auto-generated method stub
                if (e == null) {

                    img.DisplayImage(user.getprofile_pic_url(), thumbnail, false);
                } else {
                }
            }
        });
    } catch (Exception e) {
        e.printStackTrace();

    }

把你的imageview作为最终不要使它全局化你从geturl（）方法得到图像网址，它是由你在下面的例子中使用的解析所定义的

ParseFile fileObject = (ParseFile) object.get("image_file");
                User user = new User();
                user = (User) ParseUser.getCurrentUser();
                user.setProfile_pic_url(fileObject.getUrl().toString());
                user.saveInBackground();

<强>更新

去年我找到了新的解决方案，您可以通过以下代码获取与解析对象相关的用户数据，并在模型类中进行一些更改。

 void getchats() {
        pd.show();
        ParseQuery<Parse_chat_dialogs> query =    ParseQuery.getQuery("chat_dialogs");
        query.addDescendingOrder("updatedAt");
        query.whereContains("users",  ParseUser.getCurrentUser().getUsername());
        query.findInBackground(new FindCallback<Parse_chat_dialogs>() {
        public void done(List<Parse_chat_dialogs> dilogs, ParseException e) {
            if (e == null) {
                pd.hide();
                dialoglist = (ArrayList<Parse_chat_dialogs>) dilogs;
                adp = new ChatDialogAdapter(Chat_list.this, dialoglist);
                list.setAdapter(adp);
                for (int i = 0; i < dialoglist.size(); i++) {
                    ParseQuery<User> query = ParseQuery.getQuery("_User");
                    query.whereEqualTo("username", dialoglist.get(i).getUsers().trim()
                            .replace(ParseUser.getCurrentUser().getUsername(), "").replace(",", ""));
                    User user = new User();
                    try {
                        user = query.getFirst();
                        dialoglist.get(i).setFirstname(user.getFirstname());
                        dialoglist.get(i).setLastname(user.getLastname());
                        dialoglist.get(i).setProfileurl(user.getprofile_pic_url());
                        adp.notifyDataSetChanged();
                    } catch (ParseException e1) {
                        // TODO Auto-generated catch block
                        e1.printStackTrace();
                    }
                }

            } else {
                Toast.makeText(Chat_list.this, e.getMessage(), Toast.LENGTH_SHORT).show();
            }
        }
    });
}

如上例所示，我在parseobejct模型类中添加了三个新参数，用于存储用户的firstname，lastname和profile url的值。 我也在分享模型类以获得更多想法

@ParseClassName("chat_dialogs")
public class Parse_chat_dialogs extends ParseObject {

private String firstname;
private String lastname;
private String profileurl;

public String getFirstname() {
    return firstname;
}

public void setFirstname(String firstname) {
    this.firstname = firstname;
}

public String getLastname() {
    return lastname;
}

public void setLastname(String lastname) {
    this.lastname = lastname;
}

public String getProfileurl() {
    return profileurl;
}

public void setProfileurl(String profileurl) {
    this.profileurl = profileurl;
}

/////////////////////////////////////////////////////////////////////////////
public String getLast_message() {
    return getString("last_message");
}

public void setLast_message(String value) {
    put("last_message", value);
}

public String getUsers() {
    return getString("users");
}

public void setUsers(String value) {
    put("users", value);
}
}

Answer 2

这个怎么样！

不要在适配器类中使用AsyncTask，而是在MainActivity中使用它，您可以在其中为listview设置适配器。在Callback中的done方法或postExecute中更新对象/对象并调用notifyDataSetChanged（）。

所以，基本上你可以在你的适配器类中有一个更新方法，比如说，

public void updateObject(int pos, byte[] byteArray){
     //Assuming your Profile Object has some member to store this image data
     friends.get(pos).setImageData(byteArray); //friends is the list in adapter class and setImageData may be the setter in your Profile object class
     notifyDataSetChanged();
    }

并且在getView（）中，您可以执行类似这样的操作

profileImageBitmap = BitmapManager
                    .getBitmapFromByteArray(friends.get(pos).getImageData);
friendImage.setImageBitmap(profileImageBitmap);