Android download image from url and display in listview
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Download JSON data from http url DownloadTask 2. The project is available on git.
In next part B shows you how to achieve this. The times we need to download the image using web request and then save the image in phone and set this to the particular ImageView, this will be the normal flow for setting an ImageView url from web server. My code is below as well as my layouts, so far the app works in downloading the data.
Step 10 : You will get your output like below: Keep visiting for more updates on Android and other technologies. Sin Complete Example Download Android UIListView Written by: Nilanchala A blogger, a bit of tech freak and a software developer. When you scroll the ListView, it will re-use the old itemview for the new row. I think the http request may cache the image. Some of the social characteristics of AsyncTask are as follows An asynchronous task is defined by 3 generic types, called Params, Progress and Result, and 4 steps, called onPreExecute, doInBackground, onProgressUpdate and onPostExecute. The onProgressUpdate method receives progress updates from doInBackground method, which is published via publishProgress method, and this method can use this north update to update event thread The onPostExecute method handles results returned by doInBackground method. I am unable to catch outofmemory exception. So you will see the old image in the new row.
Download Images by AsyncTask in ListView Android Example - The times we need to download the image using web request and then save the image in phone and set this to the particular ImageView, this will be the normal flow for setting an ImageView url from web server.
Loading images is the most common task for Android apps. Loading image task can be very simple. But if the image size is very big or there are lots of images to be downloaded, it will take a long time. During the downloading progress, all android UI will freeze. Therefore, we have to download images in different thread from main thread UI thread. In this Android tutorial, I will give an example to show how to use Asynctask to download a list of images. At the beginning, I will create a ListView. In each row of the list, there are one image from internet. Therefore, we need to download the image in each row view for the list in the ArrayAdapter. For more information about ListView and ArrayAdapter, please check post:. First, let show the MainActivity. We are using one customized ArrayAdapter to generate the row view for ListView. We create a ListView and show the images in the ListView. However, it is a big problem when you compile and run the app in your devices. The ListView response is horrible slow and sometimes it looks like no response at all when we drag the ListView up and down. That is because we are downloading the image on the main thread or the UI thread. To solve ListView hang problem when downloading the image, we have to move the downloading logic in a different thread. Download Image in AsyncTask Example As Android developers guide mentioned, AsyncTask must be subclassed to be used. Therefore, we will create subclass, DownloadAsyncTask, in our ImageAdapter. Once the ListView request a row View from ImageAdapter, we will start a new AsyncTask and download the image in the background. In the DownloadAsyncTask class, we will override the doInBackground method which will be called to start download the image and onPostExecute method which will update our ListView when the image downloading in AsyncTask finished. Here is the subclass of AsyncTask: private class DownloadAsyncTask extends AsyncTask { Override protected ViewHolder doInBackground ViewHolder... To instantiate the subclass of AsyncTask and start to download the image, we have to change our getView function a little bit. Instead of loading the image immediately in getView, we create a new AsyncTask class and call AsyncTask. Now you can compile and try the new app in your device. The performance is getting much better. The ListView scrolls smoothly and image downloading also works fine. If you still have problems about downloading images in ListView, you can leave the reply and I will answer your questions if I can. Therefore, there maybe only 5 Views existing to serve the whole ViewList. And you will see that images are refreshed. In my example, there is no cache mechanism. I think the http request may cache the image. I think I will update my example later to support the local cache. Thanks I think your code is prone to errors due to possible configuration changes like orientation recreating the activity, so the viewholders keep pointing to the old images, as well as leaking them. I think after you make some configuration changes, like orientation, the app will recreating the activity. But this is not the reason why the viewholders keep pointing to the old images. For ListView in Android, it will only create the necessary number of itemview to fit the space. When you scroll the ListView, it will re-use the old itemview for the new row. So you will see the old image in the new row. To avoid the app downloading the images all the time, you can implement some cache mechanism. So the refresh speed will be fast. For advanced usage, please check this two post:.
