I have some issues figuring out the use of aSynctask, threads and downloading images. I've made a class that downloads image but doesn't implement any thread, asynctask or whatsoever.
At the moment i'm only using one asynctask to accomplish steps 1 and 2. This takes around 10 seconds with my tablet.
I have thought of 3 steps how the application would work/proceed.
Download the most important information from url, which is in JSON format and save it into sqlite database. This is the most relevant information that other steps need to have, in order to proceed. This takes around 2 seconds at most at the moment and I am saving this into database.
Query into my database to get more urls from the previous JSON data and download even more information from the same site (30 different URL's) and save the JSON into my database. This takes around 5 seconds at the moment within the single asynctask. I was thinking about separating this into 3(?) threads if possible.
Query database again to get information that step 2 provided and download approx 200 from different URLS, images that are of size ~150px and save these images to device storage. All of the previous steps have to be done before I can do the downloading. This has to be split up into multiple threads also so I can download as many images fast as possible.
I was wondering what would be the smartest way to use asynctask for this task and the separate threads. How many threads would you think that I would have to use (of course, I'll figure this out later on when I'm optimizing). Should I first use the asynctask to download step 1 and on post execute start the other threads? Should I create the other threads within this class that has nested async class.
Thanks a lot at least for reading all this and possibly for your help.
Edit: oh I'm using a service to start the asynctask.
The only reason to make multiple threads downloading different images is if server would take some time to query for the image and as a result you are idling and not actively pumping data. But if it is not the case then your device is working as fast as your connection allows you. Hope it makes sense.
Related
I have created an app and sorry for the noob question.I am trying to upload data and images from my phone and sqlite to my server via php.
I would like to update the timestamp only after both data and images are done uploading and even if it stops at 90% it should not update the timestamp.How can I achieve it?
I have tried upadating with async (2 parallel async for 2 different php)But I the timestamp is updated only when either of the process is completed .As I dont know how much time its going to take my upload time is not perfect all the time.How can I solve this problem?
Summary:
1.Data
2.Images
2 phps triggered from 2 different/parallel async
Upload both and update timestamp in sqlite ,if it stops in-between dont update timestamp?
I really appreciate any help.I am stuck here from 2 weeks now and I dont know how to solve it.
I don't see this has to do with Android.
However, if you're uploading your data from an Android client, and you know how much data and how many images need to be uploaded, you can just use a CountDownLatch.
That is, create a separate thread, to update the timestamp, locked by a CountDownLatch variable, that is shared by all uploading threads. After each thread finishes its work, just do a countdown on the latch. Hence, when the latch reaches 0, it will execute your timestamp update.
Keep two lastuploadedtimes in Shared preferences. One for de data task and one for the images task. Let every task in onPostExecute() update its lastuploaded time when it is completely done and there were no errors.
I am working on a project in which i have to get data tables present in mysql database on server. Now i have to insert that tables in my android application.
I had successfully achieve that functionality using Json Parsing and asynctask and sqlitedatabase, I have written php code by which i am fetching data from mysql server to my application.
Problem in this approach :
Time : As i am fetching that data from server in my Launcher Activity, My activity starts and take about 10 min to get all data from server. I want to reduce that time, I dont want that much delay, 5-10 sec will be fine
Everytime my application starts it goes in that fetching mode. which result in 10 min of loading page.
I dont want this, I want something that checks for the changes in database present on server, if there is a change then it should start fetching on background itself. I am thiking of service with alarm manager , but i dont know how to achieve all that with service. Should i use asyncTask in service or something else.
I am not sure if that detail is sufficient or not but i will give you detail explanation if needed. Any help in this will be appreciated, If my approach is wrong then I would be more then happy to change my approach to an optimized way.
Use Java threads instead of AsyncTask.In thread you could not access the UI.But performance point of view java thread is efficient for downloading large data.
Here some benefits of thread:
Network operations which involve moderate to large amounts of data
(either uploading or downloading)
High-CPU tasks which need to be run
in the background.
I'm new to Android programming and I have a threading issue.
I'm basically populating a GridView with images from 50 or so URLs, but those URLs will not be known until I retrieve a JSON object from an already known URL. I know that I have to fire off a bunch of threads for each URL download (using the AsyncTask class).
How can I effectively queue these threads so that the JSON thread is executed and finished first, so I can use data retrieved from that thread when I fire off those 50 image threads immediately after?
Do not start 50 threads. Use a single thread. While this should be separate from the UI thread for responsiveness, there is no need to spawn multiple threads, and certainly not one thread per URL.ce
Simply make your JSON network call, then parse the response, then (in the same thread) loop through the URLs requesting each one, and decoding the result into a Bitmap. You'd them add them within some model object to the Adapter for your GridView, which would automatically trigger the GridView to update on the UI thread.
There are better practices here, such as lazy loading, caching, and displaying a placeholder image while images are loading, but the exact implementation becomes too complex to describe here. Search for WeakReferenceMap and LruCache to find examples of the best practices for dynamic image loading into an AdapterView.
Well, you could just run the first fetch and when this is done, fire the 50 threads from this main thread. As Android 3.0 and later will kill your app when you do network communication from the UI thread, an AsyncTask could be a way for to fetch the JSON. When this returns it could fire the other threads.
One thing you should still consider is that Android is, as powerful as it is, still a device with limited capabilities. 50 Threads may use more resources that the target handset has and thus your app may be killed by the system (e.g. because of OOME). So wile on a desktop 50 threads don't sound much, they are much on a phone.
Also IIrc, there is a limit in the http spec, that one may only have 4 (?) simultaneous connections to one remote server. So consider queuing up the image loading requests and fetching them one after the other.
Hey guys i have a problem. I have a listview that is dynamically filled. Each row contain images and text, that are retrieved from a web service call ( i get image link in web service call, and I retrieve drawable after the web service call is finished ).
The question is this: If I have, let's say 200 images that I have to get, it is faster to pass every link to a thread and download the image in that thread, or should I use only one thread to get all of them? Or, is there any other possibility to obtain that images faster?
Thanks,
Arkde
With multiple Threads you reduce the risk of connection timing out causing all of your downloads to be held up. But you certainly don't want 200 threads either.
As was mentioned above, you should try to download images as necessary. I doubt your users are going to view all 200 images everytime they pop into that list.
I am working on a project where i need to hit a web service download the data which is JSON and will be represented in a list. And all the list items have there thumbnail url's which would be downloaded and displayed in the list item.
I have done the entire calling part with both a ThreadPoolExecutor and a AsyncTask.
But from a design perspective which is a better option out of:
1. ThreadPoolExecutor
2. AsyncTask
Few adv. of ThreadPoolExecutor:
1. User can define no. of concurrent threads that can be executed.
2. Cancelling all the request at once.
Few adv. of AsyncTask:
1. Internally it uses a ThreadPoolExecutor, however we cant define no. of threads that run simultaneously.
2. Cancelling a single request is easy.
3. Ability to attach and detach a task.
4. Updating the UI from doInBackground is simple.
I know more advantages of AsyncTask, however for a simple application like fetching data from a web service and later on fetching images.
Which would be more appropriate a AsyncTask or ThreadPoolExecutor? If you can provide a few reasons regarding your choice it would be helpful.
I have read a few article here on SO but none that compares the two. If there are any that i missed sorry for the trouble could you please post me the link for the same.
Thanks in advance.
I consider that AsyncTask is useful if you want to load thumbnail using a series "cascade-call": in the onPostExecute, you can start the next AsyncTask to download the next thumbnail.
But if you want to improve efficiency, I suggest using ThreadPoolExecutor. This is a sentence from developer.android.com:
Thread pools address two different problems: they usually provide
improved performance when executing large numbers of asynchronous
tasks, due to reduced per-task invocation overhead, and they provide a
means of bounding and managing the resources, including threads,
consumed when executing a collection of tasks. Each ThreadPoolExecutor
also maintains some basic statistics, such as the number of completed
tasks.
In conclusion, ThreadPoolExecutor was probably designed for cases such as your; for this reason, I suggest you this class.