在单声道中为android加载图像异步的问题

时间:2012-09-21 09:07:06

标签: android asynchronous mono xamarin.android

我开始开发一个新的Android单声道应用程序,需要我从远程服务器加载大量图像。为了做到这一点,我编写了一个视图,我可以插入布局,并在后台加载图像。这非常好用,直到我在ListView的适配器中使用它,这是我主要计划使用它的地方。应用程序加载一些图像而不加载其他图像,并将它们加载到错误的位置。滚动列表后,它会立即开始正确加载图像,但显示的第一个图像不完整且错误。我尝试过不同的策略来运行后台进程(asynctask,threadpools等),并且都有同样的问题。这是代码:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

using Android.App;
using Android.Content;
using Android.OS;
using Android.Runtime;
using Android.Views;
using Android.Widget;
using Android.Util;
using System.Net;
using Android.Graphics;
using ListViewExample;
using System.Threading;

namespace klvpn.components
{
    public class WebImageView : RelativeLayout
    {
        ImageView theImage;
        TextView waitingTxt;
        Activity context;
        Uri imageUri;
        WebClient wc;

        public WebImageView(Context context, IAttributeSet attrs) :
            base(context, attrs)
        {
            this.context = context as Activity;

            this.SetBackgroundColor(Android.Graphics.Color.Black);
            this.SetGravity(GravityFlags.Center);
            waitingTxt = new TextView(context);
            waitingTxt.SetText("...", TextView.BufferType.Normal);
            AddView(waitingTxt, new LayoutParams(LayoutParams.WrapContent, LayoutParams.WrapContent));

        }

        public void SetImageSize(int width, int height)
        {
            LayoutParameters.Width = width;
            LayoutParameters.Height = height;
        }

        public void SetImageUriStr(string uriStr)
        {
            imageUri = new Uri(uriStr);

            if (theImage == null)
            {
                theImage = new ImageView(context);
                AddView(theImage, 0);
            }
            wc = new WebClient();
            wc.DownloadDataCompleted += new DownloadDataCompletedEventHandler(wc_DownloadDataCompleted);
            wc.DownloadDataAsync(imageUri);
        }

        void wc_DownloadDataCompleted(object sender, DownloadDataCompletedEventArgs e)
        {
            if (e.Error != null)
            {
                context.RunOnUiThread(() =>
                {               
                    theImage.SetImageResource(Resource.Drawable.noImage_x);                  
                    string error = "URI:" + imageUri.OriginalString + "\n" + e.Error.Message;
                    Log.Error("WebImageView", error);
                });
            }
            else
            {
                Bitmap bmp = BitmapFactory.DecodeByteArray(e.Result, 0, e.Result.Length);
                context.RunOnUiThread(() =>
                {
                    theImage.SetImageBitmap(bmp);
                });
            }
            wc = null;
        }

        protected override void OnDetachedFromWindow()
        {
            base.OnDetachedFromWindow();
            if (wc != null)
            {
                wc.CancelAsync();
            }

        }


    }
}

并且适配器的GetView方法如下所示:

public override View GetView(int position, View convertView, ViewGroup parent)
        {
            var item = this.Episodes[position];
            var view = convertView;
            if (convertView == null || !(convertView is LinearLayout))
            {
                view = context.LayoutInflater.Inflate(Resource.Layout.EpisodeItem, parent, false);
            }

            var imageItem = view.FindViewById<WebImageView>(Resource.Id.imageItem);
            var textTop = view.FindViewById<TextView>(Resource.Id.textTop);
            var textBottom = view.FindViewById<TextView>(Resource.Id.textBottom);

            //imageItem.SetImageResource(item.Image);
            imageItem.SetImageSize(100, 36);
            imageItem.SetImageUriStr(item.ImageUri);
            textTop.SetText(item.Name, TextView.BufferType.Normal);
            textBottom.SetText(item.Description, TextView.BufferType.Normal);

            return view;

        }

任何想法如何解决这个问题?我在MonoTouch中使用了这个策略并且非常好用,因为图像下载是封装的,用户不必等到所有内容都加载才能看到它们。

由于

1 个答案:

答案 0 :(得分:0)

我建议使用该库:http://code.google.com/p/android-query/ 它非常简单,集成速度很快。