The app I'm currently developing needs to send images and text to a webservice, and so far so good. The app works fine, but the next step is to make it keep sending when the user exits the app or changes to another app.
How do I achieve this?
I've looked at the background agent function, but that doesn't seem to be what I want. I do not want to wait every 30 minutes and then try to send for 25 sec with the periodic agent, and the users will almost never be in the very limiting state that the resource-intensive agent requires (over 90% battery life, must be on wi-fi etc).
Am I missing something obvious here? Only sending pictures and text when the user has the app active is a big down side.
I'm afraid it is not possible to do what you require with the current WP7 OS. The Windows Phone 7 OS has been designed to restrict applications in such as way that the user's security is protected, battery life is prolonged and they have a consistent experience. Allowing any application to execute arbitrary code in the background, without imposing constraints on execution time or duration would allow people to write applications that are extremely resource intensive. This is not good for the end user!
The "periodic" or "resource-intensive" agents, as described on MSDN, are your only options.
Related
I am writing a (Django-based) website which is working just fine. It displays a list of sensors and their status. If a new sensor is attached, the user needs to wait for a certain amount of time until it is warmed up and ready to use. Also, when the sensors are updated (which the user can trigger, but can also be done automatically by the system) - the user needs to wait.
On the server side I have all signals/Status updates/whatsoever available. Now I want to create an overlay for the current webpage where the statuschange is displayed for x seconds and userinput is disabled.
I have no clue what technology to use. I could frequently ask for updates client -> server but that doesn't feel like the correct way. Any suggestions on what to search for?
No code here because the answer is probably independed of my website code
Standard solution is to use Ajax (JavaScript) or similar to get state from your backend on specific intervals, that is the approach you're mentioning.
You can also "push" changes from your backend to frontend using WebSockets but that is a bit more complex. A popular framework is socket.io, I recommend you take a look at it.
I'm have written a C++ application that is running as a Windows service to limit the volume of a Windows 7 computer. The user can specify different rules for different days and times and the service will smoothly change the volume. To implement this I use the IAudioEndpointVolume interface. In general it works like intended...
However, there exists a strange behavior I cannot explain yet. When switching users the volume suddenly drops but it does not generate a notification as one would expect. What is also strange is that the sliders in the SndVol.exe show the correct value for the volume.
Because of the missing notification my program cannot react to this change and as a result it cannot perform its intend anymore.
I have discovered that the volume will switch back to its correct volume again if I move the volume slider a bit. Of course this generates a notification that will be handled by my service. My service will then force the correct volume.
I don't understand why the volume changes without being visible in SndVol.exe and without creating a notification. Switching back to the first user account does not solve the problem. Even after logging out the volume is still at the wrong level.
As far as I have seen the documentation about the IAudioEndpointVolume interface does not mention anything about different user session.
Any ideas on what might cause this problem or what I could try to fix it?
Your service runs in session 0, the isolated session that prevents malware from exercising shatter attacks. The user's desktop runs in another session, there can be multiple. The WASAPI documentation is silent about exactly how an audio session gets mapped across Windows sessions. You have a very strong hint that it doesn't from the way it behaves.
There are ominous words in the section that talks about grouping parameters. A construct that primarily exists to allow Sndvol to identify processes that share the same volume control. It quotes Explorer as an example, a process that can be started more than once but still has a single volume control. A process that doesn't want to share uses session identifier GUID_NULL to select the default session in IAudioSessionControl::SetGroupingParam() or simply omits the call altogether since that's the default.
And the behavior of Sndvol, it only displays volume controls for the processes that run in the desktop session. You can't see the processes in another desktop session. Giving a very strong hint that audio session GUID_NULL is specific to the session in which it got created.
So quite unlikely that you can find a workaround for it as long as you do this with a service.
Instead, consider running your program as a normal windowless process that runs in the user's desktop session. Getting started by the Run registry key or a Startup folder shortcut or the task scheduler.
Well, after some time I am now quite confident that the volume change is caused by the 3rd party driver we are using. This driver has it's own volume control mechanism. I do not experience the change anymore after just starting the drivers' control GUI. Even after a restart the problem seems to be fixed. However, after some time it gets broken again for a reason I cannot figure out. But this only happened because some security settings prevented the drivers' control GUI to start when logged in as non admin. I fixed this now and expect everything to work now.
Furthermore it looks like that all user sessions share the same volume control. That means if I change the volume with SndVol in one user session the same change happens in the other user session. My service receives notifications for all these changes. So it looks like that I did not receive a notification when switching between users because the change was caused by the driver's control GUI starting when logging in as administrator. But this change happened in the driver, a lower layer, so that Windows is not aware of the change.
The driver we are using is the kX Audio Driver.
I'm currently developing a mobile app using Sencha Touch 2 and Phonegap. It's a game where you can "check-in" at some places and get some points every time you do a successful one (as in Foursquare).
I'd like to make it impossible for a clever guy (for example, someone that has decompiled my apk) to execute the REST web service (for example, mywebservice/checkin?access_token=abcde&latitude=12345&longitude=6789) with his computer or any other device outside of the app.
Do you have any idea of how I could achieve this ?
Thanks a lot,
In absolute terms, what you are looking for is impossible - if the app on the device contains the key and code necessary to send a valid message, and the device allows the user to decompile apps, then anyone can theoretically reverse engineer it and send whatever messages they want.
In practical terms though, it isn't worth worrying about - nobody will put that much effort into it, and you can probably detect accounts with suspicious activity fairly easily. Just use https and a simple token from the app code to stop anyone who can see the network activity but won't go as far as digging into the app code.
Couple options (depending on your exact scenario):
Bake user info and the app key into the security API key. This would ensure only valid account holders can use the API. Take a look at OAuth
Monitor per account or per connection service activity and look for any suspicious patterns. For example, if the app is operating in user think time then you would expect low numbers of calls per second.
I need a way to download ( from a server ) and execute a file every month automatically and invisibly to the user.
How can I do that ?
Don't blindly check for updates on a schedule. Instead, check when the user starts your application (every time, or every 10th time, or every 30th day, but only when the app gets used).
Users hate it when an application they aren't running is taking up resources.
As Steve Jessop points out, it may also be good to occasionally check again if the app stays running for a long time.
Installing a "Scheduled Task" is still the way to go, but set it to run manually instead of on a periodic schedule, then your app can trigger it. An app can trigger a task that executes with higher permissions than the app itself (creating the task in the first place requires full admin rights). The task also remembers the last time it ran which is useful for keeping traffic down.
An application that you build as a Windows service will run in the background and can do what you want.
Microsoft Windows services, formerly
known as NT services, enable you to
create long-running executable
applications that run in their own
Windows sessions. These services can
be automatically started when the
computer boots, can be paused and
restarted, and do not show any user
interface. These features make
services ideal for use on a server or
whenever you need long-running
functionality that does not interfere
with other users who are working on
the same computer.
Least intrusive way is just to check when the application starts. (Every time, or every 10th time, or whatever). I know other large apps don't do that, but as a user I really hate it, perceive these apps as "bloat" and avoid when possible. (Example: iTunes). Anything else just clogs up my computer when I'm trying to do something else.
Also, you'd better make sure the code is safe to run; use a digital signature to be sure that the code is really from you. Otherwise you're vulnerable to a man-in-the-middle attack: I could set up an imitation server and send evil code to your users. (Or hack your server and upload evil code to your server for your users to get. Etc. etc.)
I am developing a Windows Phone app where users can update a list. Each update, delete, add etc need to be stored in a database that sits behind a web service. As well as ensuring all the operations made on the phone end up in the cloud, I need to make sure the app is really responsive and the user doesn’t feel any lag time whatsoever.
What’s the best design to use here? Each check box change, each text box edit fires a new thread to contact the web service? Locally store a list of things that need to be updated then send to the server in batch every so often (what about the back button)? Am I missing another even easier implementation?
Thanks in advance,
Data updates to your web service are going to take some time to execute, so in terms of providing the very best responsiveness to the user your best approach would be to fire these off on a background thread.
If updates not taking place (until your app resumes) due to a back press is a concern for your app then you can increase the frequency of sending these updates off.
Storing data locally would be a good idea following each change to make sure nothing is lost since you don't know if your app will get interrupted such as by a phone call.
You are able to intercept the back button which would allow you to handle notifying the user of pending updates being processed or requesting confirmation to defer transmission (say in the case of poor performing network location). Perhaps a visual queue in your UI would be helpful to indicate pending requests in your storage queue.
You may want to give some thought to the overall frequency of data updates in a typical usage scenario for your application and how intensely this would utilise the network connection. Depending on this you may want to balance frequency of updates with potential power consumption.
This may guide you on whether to fire updates off of field level changes, a timer when the queue isn't empty, and/or manipulating a different row of data among other possibilities.
General efficiency guidance with mobile network communications is to have larger and less frequent transmissions rather than a "chatty" or frequent transmissions pattern, however this is up to you to decide what is most applicable for your application.
You might want to look into something similar to REST or SOAP.
Each update, delete, add would send a request to the web service. After the request is fulfilled, the web service sends a message back to the Phone application.
Since you want to keep this simple on the Phone application, you would send a URL to the web service, and the web service would respond with a simple message you can easily parse.
Something like this:
http://webservice?action=update&id=10345&data=...
With a reply of:
Update 10345 successful
The id number is just an incrementing sequence to identify the request / response pair.
There is the Microsoft Sync Framework recently released and discussed some weeks back on DotNetRocks. I must admit I didnt consider this till I read your comment.
I've not looked into the sync framework's dependencies and thus capability for running on the wp7 platform as yet, but it's probably worth checking out.
Here's a link to the framework.
And a link to Carl and Richard's show with Lev Novik, an architect on the project if you're interested in some background info. It was quite an interesting show.