So I have been struggling with the best way to load images in a ListView in Android for a while.
The images come from a server, so can take some time to load. From what I understand there are only 2 ways to implement this:
1 - Load the images on the main thread - This leads to have the correct images display immediately when the view displays and scrolls, but gives poor scrolling performance and can lead to the app hanging and crashing.
2 - Load the images in an AsyncTask. This means the images will be blank when the list display or scroll, but eventually display. Because of caching done by the list, you can also get the wrong image for an item. But this gives good performance and scrolling, and does not hang/crash.
Seems like neither solution works correctly. There must be a solution that works?? I have seen other posts like this, but the answer seems to always be 1 or 2, but neither is a good solution...
My code for the list adapter is below.
The HttpGetImageAction.fetchImage() method either executes an async task, or fetches the image on the main thread depending on a flag I set. I also cache the images locally and on disk once they have been loaded, so the issue mainly occur the first time (but the cache is only for 100 images, and the list has 1000s)
public class ImageListAdapter extends ArrayAdapter<WebMediumConfig> {
Activity activity;
public ImageListAdapter(Activity activity, int resourceId, List<WebMediumConfig> items) {
super(activity, resourceId, items);
this.activity = activity;
}
class ImageListViewHolder {
ImageView imageView;
TextView nameView;
TextView descriptionView;
TextView statView;
}
public View getView(int position, View convertView, ViewGroup parent) {
ImageListViewHolder holder = null;
WebMediumConfig config = getItem(position);
LayoutInflater mInflater = (LayoutInflater)this.activity.getSystemService(Activity.LAYOUT_INFLATER_SERVICE);
if (convertView == null) {
convertView = mInflater.inflate(R.layout.image_list, null);
holder = new ImageListViewHolder();
holder.imageView = (ImageView)convertView.findViewById(R.id.imageView);
holder.nameView = (TextView) convertView.findViewById(R.id.nameView);
holder.descriptionView = (TextView)convertView.findViewById(R.id.descriptionView);
holder.statView = (TextView)convertView.findViewById(R.id.statView);
convertView.setTag(holder);
} else {
holder = (ImageListViewHolder) convertView.getTag();
}
holder.nameView.setText(Utils.stripTags(config.name));
holder.descriptionView.setText(Utils.stripTags(config.description));
holder.statView.setText(config.stats());
if (MainActivity.showImages) {
HttpGetImageAction.fetchImage(this.activity, config.avatar, holder.imageView);
} else {
holder.imageView.setVisibility(View.GONE);
}
return convertView;
}
}
You should never load images on the main thread. Any network calls should be done asynchronously and should not be done on the main thread. Your images might load quickly (on the main thread) because you may have a good internet connection, have small images and/or have few images. But imagine what would happen if someone using your app has a slower internet and then one day your list grows to hundreds!
The approach below is a well accepted practice for loading scrollview content
a) load your text content as you load the scrollview. Again the loading should be done async but you can show a loading view until the download completes
b) Show image
placeholders while the image loads on each cell
c) Load the images
asynchronously
Using a library such as Picasso would help immensely because there is a lot of boilerplate code which you'd need to handle otherwise such as
cancelling image download when a cell is reused and
starting a new download for a reused cell
caching
retrying a failed download
Hope this helps.
Use Glide [https://github.com/bumptech/glide] or Picasso [http://square.github.io/picasso/] - both libraries are very similar, and easy to use, have caching, work in background, allow placeholders ets.
Usage is as simple as:
Picasso.get().load("http://i.imgur.com/DvpvklR.png").into(imageView);
Simple Solution: Glide.
Glide is a fast and efficient open source media management and image
loading framework for Android that wraps media decoding, memory and
disk caching, and resource pooling into a simple and easy to use
interface. Glide supports fetching, decoding, and displaying video
stills, images, and animated GIFs.
You can load the image like:
GlideApp.with(context)
.load("http://via.placeholder.com/300.png")
.into(imageView);
Refer for more info:
https://guides.codepath.com/android/Displaying-Images-with-the-Glide-Library
https://github.com/bumptech/glide
Use Glide library.. Its recommended by Google.
Step 1:
Use latest Glide Version 4 dependency (https://github.com/bumptech/glide)
implementation 'com.github.bumptech.glide:glide:4.8.0'
annotationProcessor 'com.github.bumptech.glide:compiler:4.8.0'
Step 2:
Glide.with(MainActivity.this)
.load(url)
.apply(new RequestOptions().placeholder(R.drawable.placeholder).error(R.drawable.error_image))//this line optional - you can skip this line
.into(imageview);
use picasso or Glide Library
What these library do , is that they image url from u and download them and save it in cache so that whenever you open the same image another time it will load faster and it prevents the usage of the network
Picasso
http://square.github.io/picasso/
Glide
https://github.com/bumptech/glide
You can try UnivarsalImageLoader which is quite Fast and Optimised.
It supports Multithread image loading (async or sync) and high level of customization.
https://github.com/nostra13/Android-Universal-Image-Loader
Here's how I do it
First I always create the RecyclerView.ViewHolder to which I pass a Func<int, Bitmap> image_provider (or you can pass some sort of lamda?) which when called will retrieve the image for a specific Id, if it can't it will show the default loading image
Everything is stored in a fragment (which I call a DataFragment) which has retainstate set to true.
First load a list of json objects that tell me which images I must show, this happens inside the data fragment so it will go on if there is a configuration change
I send that info to the adapter using a method like SetItems(MyImages)
Then I start a new thread that will load the images (while allowing the user to work)
I do this with the TPL library, the closest approximation for Android is Anko Async but you can also do it with AsyncTask, the problem is that I send a lot of messages to the main thread, so to do it with AsyncTask you have to give it a handler to the main thread which will send messages.
In the thread I loop through all the images I have to download, and download them and send a message to the DataFragment which sends it to the currently attached Activity which triggers the NotifyItemChanged method in the adapter
The adapter on creation receives a Func<int, Bitmap> image_provider which it invokes and retrieves the image from memory
I know it sounds a bit messy, so if you want code examples I can give them , but they are in C#
In your app level gradle implement below repository:
implementation 'com.squareup.picasso:picasso:2.5.2'
Put below line where you want to load image
Picasso.with(getApplicationContext()).load(config.avatar).into(imageview);
just use Picasso.get().load("http://i.imgur.com/DvpvklR.png").into(imageView); or
Glide.with(getApplicationContext()).load("image_url").asBitmap().centerCrop().into(new BitmapImageViewTarget(imageView)
in adapter like any view and done no extra efforts required
Have you ever been going through apps like 9gag, Instagram or Facebook? You notice, that while scrolling the pictures load into the recviewer. They sort of come in one by one while you can still use the app.
I have implemented my own custom recviewer and am stuck right here:
pictures = KumulosHelper.Pictures.getNewestXPhotosFromUserInRange
(strUsername, "6", startNumberOfTask.ToString(), "1");
foreach (var picture in pictures)
{
startNumberOfTask++;
var metrics = Resources.DisplayMetrics;
lstData.Add(new DataForProfile()
{
imageId = startNumberOfTask,
img = (Bitmap.CreateScaledBitmap
(KumulosGeneral.DecodePhotoFromBase64(picture.photo),
metrics.WidthPixels, metrics.WidthPixels, true)),
description = picture.taskId.ToString()
});
}
Where I type in "6" is where I get 6 pictures to load into my recycle viewer form the server. I can type in 10 or 20 and it continues loading those pictures. So, I could probably set up a "reachedbottomevent" to continue loading new pictures when the viewer reached the end. But that would mean that the user has to wait everytime he or she reached the bottom of the matrix. This is pretty annoying. Also, the whole activity wont start untill all pictures are fully loaded.
How do I get my recview to behave like the afforementioned apps above? Some sort of "smart" loading the pictures?
Thank you for the input!
Try using the Picasso library which is very reliable and easy to use. It also loads pictures in a background thread.
https://www.nuget.org/packages/Square.Picasso/
Also, the whole activity won't start until all pictures are fully loaded.
In order not to block your UI thread try using a BackgroundWorker or a Task.
At last, if you want to load a new batch of images before the user reaches the bottom of your list, then change your logic to trigger the call for a new batch for example when the user scrolls half the table.
I'm building an app that requires me to append a bunch of views into a scrollView (as many as 70) based on the data the server sends back. An abbreviated version of how I am appending them looks like this.
if (mWallPosts != null) {
for (Map.Entry entry : mWallPosts.entrySet()) {
addPostToView((DataClass) entry.getValue(), (LayoutInflater) getActivity().getSystemService(Context.LAYOUT_INFLATER_SERVICE), mViewGroup);
}
}
and this being the addPostToView method call
View postView = inflater.inflate(R.layout.fragment_wall_post, container, false);
LinearLayout containerView = (LinearLayout) mWallView.findViewById(R.id.wall_content);
containerView.addView(postView);
There is more work that goes on, but it is irrelevant for the purpose of this post. I am also using a NavgationDrawer and the problem I am having is that when I navigate to this item the animation of closing the drawer isn't smooth (it kind of hangs for a second and snaps shut) It's pretty obvious to me that this is caused by the fact that this appending and the closing of the drawer are happening on the same thread, but I'm not sure how to resolve this issue. If I could figure out how to delay the append or something like that it would probably help. I don't think async would be of any use since it is ultimately going to run on the UI thread.
I have a ListView that loads images to the ImageView asynchronously. To achieve this i am using Android-Universal-Image-Loader
But i would like to start loading this images only when they are visible in the listview. For example if the visible items of the listview are from 5 to 9, only those should be loaded. Also if the user scrolls very fast the ListView only when stopped those items should be loaded.
What is the best way to this?
If you use "view reusing" in your listview adapter then you shouldn't do anything. UIL do it for you. UIL won't load ALL scrolled images, only those which are got in task pool (you can set set pool size in configuration). If you use "view reusing" then images which were scrolled fast won't be loaded.
Look into example project on GitHub.
UPD: Since 1.7.0 version UIL have PauseOnScrollListener.
boolean pauseOnScroll = true;
boolean pauseOnFling = true;
listView.setOnScrollListener(new PauseOnScrollListener(pauseOnScroll, pauseOnFling));
Use an OnScrollListener, the onScrollStateChanged() method is called when the ListView switches between SCROLL_STATE_IDLE, SCROLL_STATE_TOUCH_SCROLL (slower scrolling), and SCROLL_STATE_FLING (faster scrolling). With this you can choose to load new images only when the states is "Idle" or "Touch".
Addition
In the first run the visible items of the ListView aren't shown. For example when the app starts if the ListView has 4 items visible those 4 images should be loaded.
I haven't used the Universal Image Loader myself, but from what you described below you need to know how many rows will be displayed before you start downloading. Try this:
Write a Runnable to start the asynchronous downloads.
Use your ListView's built-in Handler to call the Runnable after the rows have been drawn
For example:
private Runnable loadImages = new Runnable() {
#Override
public void run() {
// Start the asynchronous downloads
}
};
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
...
mListView.post(loadImages);
}
The loadImages will be called after the ListView is drawn so you will know exactly how many rows are visible.
This is what I am doing
ProgressBar myProgressBar = (ProgressBar) findViewById(R.id.progressBar);
myProgressBar.setVisibility(View.VISIBLE);
fetchData();
mainView();
myProgressBar.setVisibility(View.INVISIBLE);
But the progressbar does not show.
fetchData takes around 5 seconds and while it is running, the progressbar should be shown.
I guess the display is not updated while the App is busy. Is there a way to update the display before I call fetchData?
You should try using an AsyncTask. This will allow you to run fetchData() using the doInBackground(...) method and post progress using onProgressUpdate(...).
In the layout file give android:visibility="visible" for the ProgressBar. And when the content is loaded u set visibity to invisible.