Develop Reference

Displaying a stack of images

Given:
A number of images (10 - 15) residing in assets folder (as practice shows, the better approach is to keep high-resolution images in assets)
Android UI thread (caching drawables in advance is already made in a background thread)
The issue:
Need to display all the images one on another smoothly and not blocking UI thread after the images are drawn.
Already used approaches:
Dynamically create a required number of ImageView and then call .setImageDrawable(). This takes a lot of time but the worst thing is that the UI thread is being blocked even after all the images are drawn on their ImageView.
Create a LayerDrawable object and pass as argument an array of the required Drawables. Then put it on an ImageView also by calling .setImageDrawable(). This option behaves the same like the one described above.
Is there a way to solve this issue? Or Android devices not capable to cope with it?

Try Picasso library:
http://square.github.io/picasso/
It has support for resources:
Picasso.with(context).load(R.drawable.landing_screen).into(imageView1);
Picasso.with(context).load("file:///android_asset/DvpvklR.png").into(imageView2);
Picasso.with(context).load(new File(...)).into(imageView3);

If you are requiring a smooth transition between images, please try viewFlipper
https://developer.android.com/reference/android/widget/ViewFlipper.html
Basically you can add imageView inside the viewflipper and start animation to move from previous to next image. I am not sure if you need user interactions like scrolling or not. You can try viewPager if user need to scroll betweens images.
Please note that Glide does provide some transition effects for switching between placeholder and image to display. But transition between images are not included, you can have a look here
http://bumptech.github.io/glide/doc/transitions.html
I hope this helps because i am not sured that if you are asking the transition between images or rendering images.

Displaying images in a Recyclerview

I have a recyclerview that I want to display images that I have saved in drawables in jpeg. For loading I was using an Async Task, but this doesn't preload or Cache them. I was told to use one of the tools like fresco or glide to do that, but which one can do the Job better?
The most important thing for me is that the app doesn't crash, but it would also be nice to be able to preload certain images already before the View is displayed and afterwards preload as many as memory allows.

You can use Fresco for this. An example for a recycler view that loads images from the network can be found here:
https://github.com/facebook/fresco/blob/master/samples/showcase/src/main/java/com/facebook/fresco/samples/showcase/drawee/DraweeRecyclerViewFragment.java

How to prevent load each row (image) in recycleview

I have to show an image into imageview in my layout for recycleview' s row.
RecycleView use ViewHolder pattern so my code is in custom ViewHolder.
To load the images I need to use an AsynkTask that return a File in onPostExecute(). In this onPostExecute() I setup imageView with Picasso.
I tried to obtain the same file without use AsynkTask. So I call directly Picaso.with()....
In this scenario, recycleview lag so much when scrolling, but i notified that Picasso cache all images.
The first scenario with AynkTask has more than one problem. Scrolling down and up for x times with 100 row make the queue of asynktask bigger.
Now, if I open a fragment of drawer, queue of Asynkask continues to load and this selected fragment make its work so slowly.
how can I fix it?

I would suggest you to checkout Image Management Library by Facebook that is Fresco that is pretty awesome and mature as compared to other Image Loading Library.
When image in a view goes out of screen it automatically recycles the bitmap, hence releasing the memory (Making scrolling smooth).
Fresco handles all the things caching of images with 3 Tier architecture ( BITMAP_MEMORY_CACHE, ENCODED_MEMORY_CACHE and DISK_CACHE).
It also reduces OOM (Out Of Memory) issues.

Which approach to use to download many images asynchronously

I've a ListView in which each row item contains many ImageViews apart from some content.
That is, there will be many list items, each containing many images.
In order to not to hold user unnecessarily, I'm showing the content first & then downloading the images asynchronously.
Currently, for each image I'm starting a new AsycTask.
Although, it working alright, but this not a good approach.
In place of this, what should I use?

use this library, best in android for image loading..
https://github.com/nostra13/Android-Universal-Image-Loader

Your scenario seems to fit exactly to use LazyLoading of images. This basically loads images in the background and shows them as soon as they're loaded.
You might want to see this:
Lazy load of images in ListView
An alternative would be using a ThreadPoolExecutor with the images to load, but the above works pretty well and is recommended.

Try using the library
http://square.github.io/picasso/
Many common pitfalls of image loading on Android are handled automatically by Picasso:
Handling ImageView recycling and download cancelation in an adapter.
Complex image transformations with minimal memory use.
Automatic memory and disk caching.

How to implement a lazy loaded list of images in a listview

What i am trying to do is toscroll through a list of images. But when i scroll down or up quickly the images are misplaced in order. A diff pic comes in the place where it was supposed to be. I have tried setting the imageview to null drawable from my imageloader library to clear any rpevious images if any. But the issue persists. What should i do

You can try to use Universal image loader
This is for listView optimization and improving performance if your listView contain images from web.
Features:
Multithread image loading Possibility of wide tuning ImageLoader's
configuration (thread executors, downlaoder, decoder, memory and disc
cache, display image options, and others) Possibility of image
caching in memory and/or on device's file sysytem (or SD card)
Possibility to "listen" loading process Possibility to customize
every display image call with separated options Widget support

Finally discovered the culprit. I was using the imageview.bringtofront() function which was causing the problem for some unknown reason. I wanted to put a part of the imageview infront of the other and was using the relative layout & bring to front. Now i removed the bringtofront() and rearranged the imageview in relativelayout so that its already in the front. Resolved. Thank you all