ListView实现Item局部刷新

来源:转载

 对于ListView数据的刷新大家都知道,改变Adapter的数据源,然后调用Adapter的notifyDateSetChanged()方法即可。

但是博主在做公司项目的时候,有个下载模块,因为可能同时下载好几个数据,所以用的listview展示所有正在下载的内容。因为下载进度要实时更新,所以要不停的调用notifyDateSetChanged刷新数据。这样会不停的重新绘制整个listview的界面,性能开销非常大。而且如果每个item有图片的话,每个item的图片都需要重新加载,就算图片做了内存缓存,刷新一下图片也会闪一下,不停的刷新就会导致各个item的图片不停的闪,体验一点都不好。

那么对于上面问题,有没有解决办法呢?当然是有的。我们可以针对某一个item进行局部更新,而不影响其它没有修改的item。那么具体如何实现的呢?我们看下面的代码。

 1 private void updateView(int itemIndex) { 2 //得到第一个可显示控件的位置, 3 int visiblePosition = mListView.getFirstVisiblePosition(); 4 //只有当要更新的view在可见的位置时才更新,不可见时,跳过不更新 5 if (itemIndex - visiblePosition >= 0) { 6 //得到要更新的item的view 7 View view = mListView.getChildAt(itemIndex - visiblePosition); 8 //调用adapter更新界面 9 mAdapter.updateView(view, itemIndex);10 }11 }

这个函数主要是根据传入的itemIndex来获取第itemIndex的数据所显示的view。itemIndex就是要修改的数据再List集合中的位置,比如我这里下载进度有更新,发了一个广播这里接收到了,需要修改该下载内容的进度条,广播接收器可以这么写:

 1 @Override 2 public void onReceive(Context context, Intent intent) { 3 AppContent appContent = intent.getParcelableExtra("appContent"); 4 if(appContent == null) return; 5 int itemIndex = 0; 6 for(AppContent appContent1 : mList) { 7 if(appContent.getUrl().equals(appContent1.getUrl())) { 8 itemIndex = mList.indexOf(appContent1); 9 appContent1.setDownloadPercent(appContent.getDownloadPercent());10 break;11 }12 }13 updateView(itemIndex);14 }

下面看Adapter的具体代码:

 1 public class AppContentAdapter extends BaseAdapter{ 2 3 private List<AppContent> mDates = null; 4 private Context mContext; 5 6 public AppContentAdapter(Context context) { 7 this.mContext = context; 8 } 9 10 @Override 11 public int getCount() { 12 return mDates.size(); 13 } 14 15 @Override 16 public Object getItem(int position) { 17 return mDates.get(position); 18 } 19 20 @Override 21 public long getItemId(int position) { 22 return position; 23 } 24 25 public void setDates(List<AppContent> mDates) { 26 this.mDates = mDates; 27 } 28 29 @Override 30 public View getView(int position, View convertView, ViewGroup parent) { 31 ViewHolder holder = null; 32 if (convertView == null) { 33 holder = new ViewHolder(); 34 convertView = LayoutInflater.from(mContext).inflate( 35 R.layout.listitem_download, null); 36 holder.statusIcon = (DownloadPercentView) convertView.findViewById(R.id.status_icon); 37 holder.name = (TextView) convertView.findViewById(R.id.name); 38 holder.downloadPercent = (TextView) convertView.findViewById(R.id.download_percent); 39 holder.progressBar = (ProgressBar) convertView.findViewById(R.id.progressbar); 40 convertView.setTag(holder); 41 } else { 42 holder = (ViewHolder) convertView.getTag(); 43 } 44 setData(holder, position); 45 return convertView; 46 } 47 48 /** 49 * 设置viewHolder的数据 50 * @param holder 51 * @param itemIndex 52 */ 53 private void setData(ViewHolder holder, int itemIndex) { 54 AppContent appContent = mDates.get(itemIndex); 55 holder.name.setText(appContent.getName()); 56 holder.progressBar.setProgress(appContent.getDownloadPercent()); 57 setIconByStatus(holder.statusIcon, appContent.getStatus()); 58 if(appContent.getStatus() == AppContent.Status.PENDING) { 59 holder.downloadPercent.setVisibility(View.INVISIBLE); 60 } else { 61 holder.downloadPercent.setVisibility(View.VISIBLE); 62 holder.statusIcon.setProgress(appContent.getDownloadPercent()); 63 holder.downloadPercent.setText("下载进度:" + appContent.getDownloadPercent() + "%"); 64 } 65 } 66 67 68 /** 69 * 局部刷新 70 * @param view 71 * @param itemIndex 72 */ 73 public void updateView(View view, int itemIndex) { 74 if(view == null) { 75 return; 76 } 77 //从view中取得holder 78 ViewHolder holder = (ViewHolder) view.getTag(); 79 holder.statusIcon = (DownloadPercentView) view.findViewById(R.id.status_icon); 80 holder.name = (TextView) view.findViewById(R.id.name); 81 holder.downloadPercent = (TextView) view.findViewById(R.id.download_percent); 82 holder.progressBar = (ProgressBar) view.findViewById(R.id.progressbar); 83 setData(holder, itemIndex); 84 } 85 86 /** 87 * 根据状态设置图标 88 * @param downloadPercentView 89 * @param status 90 */ 91 private void setIconByStatus(DownloadPercentView downloadPercentView, AppContent.Status status) { 92 downloadPercentView.setVisibility(View.VISIBLE); 93 if(status == AppContent.Status.PENDING) { 94 downloadPercentView.setStatus(DownloadPercentView.STATUS_PEDDING); 95 } 96 if(status == AppContent.Status.DOWNLOADING) { 97 downloadPercentView.setStatus(DownloadPercentView.STATUS_DOWNLOADING); 98 } 99 if(status == AppContent.Status.WAITING) {100 downloadPercentView.setStatus(DownloadPercentView.STATUS_WAITING);101 }102 if(status == AppContent.Status.PAUSED) {103 downloadPercentView.setStatus(DownloadPercentView.STATUS_PAUSED);104 }105 if(status == AppContent.Status.FINISHED) {106 downloadPercentView.setStatus(DownloadPercentView.STATUS_FINISHED);107 }108 }109 110 private class ViewHolder {111 private DownloadPercentView statusIcon;112 private TextView name;113 private TextView downloadPercent;114 private ProgressBar progressBar;115 }116 }

其实这些代码就是我上篇博文《AsyncTask实现多任务多线程下载》的例子中的,如果需要可以去下载。

 



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