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Moving to the next Activity without killing the previous one

I have got an activity where i download images from a server and display them in a gridView.
Then If i click on one of those images I open a new Activity where I display the full screen image. Now if I get back to the first activity, the one with the gridView, images are downloaded again.
I am using Picasso for displaying images either in the gridView and in the following activity.
Is there a way to avoid the downloading of the whole set of images in the gridView EVERY time I go back from the second activity?

When picasso download an image it saves it to the heap memory, if the images is too large for the heap they are not cached. So if you have grid view full of images, use picasso's ".resize()" to down scale those images and ".config(Bitmap.Config.RGB_565)" to use 16 bit colors (you won't see a difference in the quality, but there is significant difference in size).
Ex: picasso.load(url).resize(200, 200).config(Bitmap.Config.RGB_565).into(target);

Android View pager load image one by one on swipe through next page

I need to show 1000 images in viewpager from DB.The problem is if I fetch all images from DB and try to set those images to adapter,it shows Bitmap out of memory exception since heap size gets exceeded. So,I'm trying other way around which is to load images one by one when the user swipes to next page.I Googled a bit,but didn't find any appropriate solution.so any input on this is highly appreciated.

Here is all that you need : http://developer.android.com/training/displaying-bitmaps/index.html
Load Bitmaps efficiently, LRU cache, etc. etc.
To summarize, you should fetch one bitmap at a time, scale it down using inSampleSizeand use LRUCache. OR, you can use http://code.tutsplus.com/tutorials/android-sdk-working-with-picasso--cms-22149 library

Asynchronous bitmap buffering with GridView in Android

I am bulding up a grid of images for an app I'm building. It works like so:
Build up a list of Image IDs, which I must query using a different content provider each (these are images from MMS threads)
Create new activity, which hosts an ImageGridFragment. This fragment has a custom adapter that takes the grid of images, and loads each one as a bitmap asynchronously.
After images are loaded, they are cached in an LRU cache so I don't need to run unnecessary computation
So far, everything works quite well. However, I would like to pre-buffer images so that when the user scrolls down, s/he doesn't have to wait for images to load. They should already be loaded. The stock Android Gallery accomplishes. I've had a look at the source, but think there must be a more straightforward way.
To answer members' questions
Images are loaded one by one using the content://mms/part/xxx, where xxx is the ID of an image. These are MMS images, and to my knowledge, cannot be loaded as a batch process (though, maybe I'm wrong). I use a content provider in an AsyncTask to load each image
I've tried the following:
Pre buffer 30 images or so right when the fragment is created. This is not ideal because the massive I/O request, actually prevents the on-screen images from loading quickly (but the buffering does work well!)
Detect when the requested view to load is at the very bottom-right hand corner of the screen, which could work, but then would fail in the case that the GridView takes up only part of the screen. It also seems like there should be a cleaner way to do this
Thought about, but did not try, an OnScrollListener, but this will not pre-buffer images until I start scrolling, which is not ideal
So, my questions are:
Is there a good way to detect when the last GridView item is requested to load? I found that the GridView.getlastvisibleposition() method is not useful here, because it is actually returning the last element for which Adapter.getView() has been called for. If I can do this accurately, I can launch the buffer request at that time
Is there a better way to do this?

you can do right this
if(GridView.getlastvisibleposition() = mAdapter.count()-1)
how you load the images?
is it from URL or from sdcard?
are you using a image loader library?

Showing thousands of ImageViews in android

I need to load a lots of images (3500 images) to my android app (and then I will rotate with each of them in the application). But when I load each of them separately (creating new ImageView which I add to the array) then it takes about 10 seconds to load. I have tried to inflate them from XMLs since there is only 8 different images which I use but no visible changes.
I would be really grateful for any advice how to load it faster.
EDIT: I am creating a grid of hexagons, each hexagon is consisted of 6 triangles (this way I need to store only 8 different triangle images instead of storing image for each different hexagon). After the grid is loaded user can resize it. I need to load all the grid cell at once because there are many constrains between them. Also only operation I will do with the hexagons is to rotate them.

You can use cashing for bitmap images, the following tutorial link is helpful.
http://developer.android.com/training/displaying-bitmaps/cache-bitmap.html

Android loading many images into gridview

In one section of my app , I m showing images to 1024+ websites inside a gridview. When the images are not present on the devices they are downloaded with an async task and the image is saved in the data folder. The grid view has a section indexer, adapter and fast scroll associated with it.
However I have noticed that the app becomes really slow when I try to fast scroll to different positions in the app. A solution \[here\]\[1\] hints implementing a hashmap to store images. The total size of the images I have are around .3mb . Will storing the bitmap in the map help speed up the app ?