Develop Reference

How can I test my app for a specific device?

I am building an application with React Native but the app not working well on a few android devices. So I need to see what's going wrong but I don't know how to set up an emulator for a specific device. Are these problems depends on phone's brand and model or it just depends on their android versions?

Its not really possible. There's two major problems:
Software. Real devices don't ship pure AOSP like runs on the emulator. They add patches and features and there's no way to know what they actually run.
Custom UIs. Many phones provide custom UIs like TouchWhiz and the like which can override Android behavior
Hardware. If your app depends on things that are very hardware specific, like GPS or Camera, they could have issues due to hardware bugs.
If you just want to emulate a specific OS version like KitKat, or specific low memory conditions its possible via emulator configuration. If you really need to test on a device, either buy one or use a service that allows you remote control over specific devices. Amazon has a nice device farm that you can rent over AWS.

One of the biggest challenges when developing for Android is the wide variety of devices and "optimizations" manufacturers make to their Android versions.
The Android emulator is based on AOSP (vanilla Android) and was only recently published with Google services included. This is the most clean version of Android. You can use the emulator to test UI scaling for different screen sizes but it will always behave like an AOSP Android. Google packs a bunch of hardware configurations into Android Studio which you can simply select when creating an virtual device. You can always create a custom hardware profile with custom screen size and resolution. Some manufacturers also change the DPI value of the OS causing the UI to be bigger or smaller, keep this in mind when creating a custom hardware configuration.
Further, you can use the emulator to test the default behaviour on different Android versions. Again, manufacturers change their Android usually causing slightly different behaviour.
I assume that your question is focussed on different behaviour of e.g. Samsung phones having crashes only occuring in Samsung phones (Samsung can be exchanged with any other brand here). Unfortunately, there is no simple way to test this but getting your hands on the faulty device. One option is to use a cloud based test lab (e.g. Firebase Test Lab, App Center or AWS device farm) to test your code on the faulty device or rent the device at a local shop. Most bigger cities have companies renting phones and tablets on a daily or weekly basis.
In the end you will need if statements checking for a specific device, manufacturer or Android version or any combination of them and doing something slightly different to fix the undesired behaviour.
I know that this is not the answer you are looking for, but it's the best I can offer. To tell a little tale of my worst experience: I had once a bug were calling a crypto function caused a kernel panic on HTC (?) phones. This means the user opened my app and the phone rebooted. I was required to implement the entire encryption logic again just for HTC with Android 6.0.

How can I programmatically disable automatic updates from Google? (Ice Cream Sandwich)

My company makes a tablet Android app to control an industrial process. We had been using a Galaxy Tab 10.1, but as that's no longer available in the US we're evaluating the Galaxy Tab 2 10.1, running 4.03. We ship the tablet pre-installed with our app, and the app is carefully tested with the version of Android software running on the tablet.
As I was setting up one of the new tablets the setup wizard put up a message saying "You agree that your tablet may receive and install updates from Google" It wasn't asking me, it was telling me; there was no place to say "no" or disagree. Auto update is DISabled in settings.
How can I programmatically prevent a force-feed update to the tablet? Our users are connected to a local area net because the tablets are used to control other industrial products, but there is never any need to connect to the web beyond the factory walls, but we have no way to enforce that on our customers. The risk is that Google could force a change onto the tablet that might break our app.
Thanks in advance.

How can I programmatically prevent a force-feed update to the tablet?
Build your own firmware and use that rather than the stock firmware.
The risk is that Google could force a change onto the tablet that might break our app.
The risk of blocking the firmware updates is that Samsung (not Google) could deliver an update to the tablet that fixes flaws in the firmware that your customers would appreciate (e.g., better WiFi connectivity).
Please understand that the devices that you are using are consumer devices. Such devices are not intended for use "to control an industrial process". The expectation is that if you are using Android in such settings, that you would source your own device and have control over your firmware. Alas, there is not a whole lot of support for that at the moment, something I blogged about recently.

As long as you target your desired API, an update to the system should not break any functionality of your app. To answer your question, you cannot programatically disable automatic updates, it is a user function.
Check this link as well: Programatically enable/disable market auto-update

Android Tablet or iPad for Kiosk Device

We want to place a device in a store that operates as sort of a kiosk device. As in customers walk up to it and start interacting with our custom app. The app could be developed for Android or the iPad, so I'm trying to decide which one to use and would like comments on the following ideas:
Is it possible for Android or iOS to access services over the USB port? This would enable us to disable the network.
Is one particularly better for 24 hour always on?
I like the iPad as I think its supply will be more constant as we move forward and need to replace devices due to ones gone bad. Also, our app will probably work on future generations of the iPad. With Android, I'm not sure there will be that sort of consistency from the tablet vendors.
Kiosk mode? I think with the iPad by putting it in a kiosk case that removes access to the home button and turning on the restrictions we'll get what we want. What about Android? I'd rather not have to get into rooting devices and replacing their firmware.
Remote control? Any way to remotely control iOS or Android in a standard means? Our app will be a client to a master server which will obviously be able to control the app somewhat (when used purely as a display device to a customer, controlled from behind the counter).
My feeling is that neither Android tablets or the iPad is best suited for this. Are there other options?

I will try to answer your points, but know that I am probably biased towards Android, because that is where my experience lies.
With Android 3.1+, at least with the Xoom, you have full USB host capabilities. Things like USB flash/hard drives, keyboards, mice, even digital cameras, all work. If you need custom interop with a USB device, you could go as far as to write a driver for it.
24 hour always on is not good for any device with a battery, but neither is better in this situation.
While android apps are forward-compatible, bad programming practices and/or deviations from "vanilla" Android software and hardware CAN break forward compatibility. That being said, if you grab a Google Experience device like the Xoom, you won't meet as many surprises.
In Android 3.0, the navigation bar is built-in at a low level, and it is not possible for apps to remove it. Therefore, it is trivial for anyone to break a "software nanny."
I know that it is possible to control android devices remotely, but without knowing your specific needs, I can't really offer more information than that.
Good luck!

iPad NOOO believe me I am a convert to Apple for my home and business but when we went to launch kiosk the iPad FAILED Big Time.. Here are a couple of little (Big) issues we ran into.
If the device reboots you cannot auto launch you iPad app since Apple does not allow that.
There is a serious memory leak in the iPads browser. We were running javascript / CSS3 and it cratered intermittently. I literally spent 2 hours "today" on the phone with Apple getting the MAJOR run around. I finally said let me speak to an Enterprise Sales Manager as my project could mean thousands of iPads and I got NO WHERE. One Apple employee even told me they don't have enterprise sales managers.
If those weren't enough even though we are just in the proof of concept phase, we are already getting request for other options. These other options are going to require access to the OS which Apple yea right. We are moving to Android immediately.
Sorry Apple I love you but you loose here.

If your using an Ipad you should consider if it can support the power for the USB thing. Watch this Using Powered USB Port

Your idea about putting the tablet behind another piece of glass/plastic is neat. To then deal with remote controlling, you might consider doing some Bluetooth programming.
My mobile development has been primarily with iOS, so I am biased toward that SDK. I will mention that the data/sync/charge port for iOS has (I believe) never changed. Your Gen 1 iPhone sync cord works on your iPhone 4... and your iPad or iPad 2. So, in terms of third party hardware, you may see more consistency with Apple.
I haven't found a good answer regarding whether it is easier to do Bluetooth programming for iOS or Android, but I think to stay cost-effective, you might see which one is more open to third-party devices. Here is an SO post/answer about iOS and third-party Bluetooth devices; I've not found anything on Android regarding third-party Bluetooth remotes, but considering a lot of hardware running Android is third-party, your chances from a naive perspective seem pretty good. Here's the Android Bluetooth API.
Buying an iOS or Android handheld to remote control an iOS or Android tablet does seem a bit steep, but then again, maybe not. Cost also depends on your ratio of remotes to tablets. 1:1? 1:N? N:1? N:M?
The lowest end iPod goes for $229 as of May 20, 2011. Android does have more variety in terms of hardware. You may be able to get a cheap Android phone with no service plan to act as a Bluetooth remote for an Android tab.

I have provided a solution for the kiosk mode using iPad here Lock-down iPhone/iPod/iPad so it can only run one app
I am afraid that I don't really know for Android if the same thing is possible.
To address the issue of crashing applications you can use an exception trampoline (see discussion here https://blog.compeople.eu/apps/?p=275) to catch the crash and reboot your app.
If the entire device is restarted however then other apps that are on the device can be started and will subsequently be locked in.
To answer your other points:
You can use a configuration profile to control network access. Force it to use a VPN or Proxy that only allows your custom app with embedded credentials to use. That way other network access can be prevented.
Your concern over future compatibility is spot on. The Android marketplace is so fragmented then maintaining a fleet is difficult.
If you have an app that is behaving as a server and is locked in then remote control is possible.

We manufacture tablet kiosks that support both android and iPad devices. In fact we are the only iPad kiosk that has achieved apple approval.
Generally speaking i think you will have an easier time with an iPad as the software and hardware will remain more consistent over time. Which is important if you have to change out a fault unit or deploy more kiosks 6 months or year from now when the original device is no longer manufactured.

Redirecting/duplicating the UI to an external output

Is it possible in the Android framework to duplicate what is displayed on the main display (UI)?
I have a situation where I need to demonstrate my app to many people, and it would be easier to do if I can duplicate the screen contents to an external monitor/TV. I am not married to the idea of using the HDMI port, I would be happy doing this through Wi-Fi or Bluetooth or USB if need be. What I am looking for is to see if I can do something similar to what Windows does by default when a second monitor is connected.
I have been through the developer's documentation and haven't been able to find anything that would allow me to do this, but it would not be the first time I've missed something. Specifically I need to do this with an HTC Evo.

Your options are limited, mostly by your choice of device. The HTC EVO's HDMI port will only play back apps via the built-in Gallery application (videos and still photos).
You will need to use a "software projector" like Droid#Screen -- attach your EVO to a Android SDK-equipped notebook that is connected to a projector. Droid#Screen will display the EVO's screen on the notebook (and, from there, on the projector). However, the frame rate is limited to about 5-6 fps, due to limitations in the SDK tools that Droid#Screen leverages.
Or, get your hands on an HTC Droid Incredible, which supports composite output to TVs of anything on the main display via a special cable. The Samsung Galaxy Tab also supports this for anything that does not involve a SurfaceView, based on my experimentation to date. Some versions of the Samsung Galaxy S also support this, at least to some extent.
Or, use a webcam.
Or, use an ELMO (basically a webcam designed for document or device projection).

You can write a UiCloningService in jni that exposes a JNI method to clone the display. Usually, as Android is based on Linux, it will use the Linux framebuffer technology to represent display devices as dev nodes under /dev/fb* or /dev/graphics/fb*, where '*' can be 0,1,2,... depending on number of display connected.
As your device already has an HDMI port, it would be exposed via /dev/graphics/fb1, considering fb0 to be your default LCD display.
In the cloning service, you can then write to device attribute files created for the HDMI port under sysfs and, if the display driver of your device has implemented those features (which most probably would have, otherwise what point to have an external HDMI display), these features/functions in the driver will be responsible for cloning the Ui on your primary display to the secondary display.
But you would have to write the Ui cloning service in JNI.(usually device manufacturers provide such methods, if at all an Android SDK is provided by them for development on that particular device).
For eg., I have attached a UiCloningService.cpp that has a cloning JNI function for Android GingerBread on an OMAP3 platform below:
UiCloningService.cpp

How do I output to monitor from android device

I am trying to do a demo on a android device, but the screen is too small so is kinda hard to do a demo let say in a meeting room with 12 people. Although I can pass the device around the table or just simple borrow or get more devices for the demo purposes.
I understand there are devies where you can buy special USB converter to do TV-out like in iPhone, and some specific devices on Android (e.g. Motorola Incredible?) But I have to demo on a specific device where it runs standard Android build.
I understand I can do it on Android emulator but the screen refresh rate is too slow, as it will send the wrong message to the audience that the app is slow. (Or there is a way to increase the screen refresh rate for emulator?) Furthermore the emulator doesn't support multitouch. (Or am I wrong?)
Not sure if anyone

You do not have many options.
You can use Droid#Screen, but the refresh rate on it is maybe 6fps. I am not aware of any other software projector that is faster.
You failed to mention the "specific device" that you are using, so I cannot comment on whether it has TV-out capability. The HTC DROID Incredible and the Samsung Galaxy S series support composite output -- I use the DROID Incredible for this purpose a fair bit. Most of the devices that have HDMI output only support it for certain built-in apps, such as the video player.
You can rent or purchase a device projector, like an ELMO. These are fairly expensive pieces of equipment purchased new, though I see a handful of used ones on eBay at interesting prices (though watch out -- many seem to lack the AC adapter).
If you can delay the demo several months, you may be able to use a Google TV.
And that's about it, AFAIK.
Or there is a way to increase the screen refresh rate for emulator?
Get a faster computer.
Furthermore the emulator doesn't support multitouch. (Or am I wrong?)
I am not aware of a way to simulate multitouch with an emulator, though I have not gone looking for a solution there.

If you have an Galaxy S3 Android mobile phone, you can use Mobizen. It's free and the screen refresh rate is relatively good. You can control you mobile phone from you computer using your mouse and your keyboard. It's working using USB, 3G or Wifi connection.

I have used this Android screencast tool: http://code.google.com/p/androidscreencast/ in past demos, but again the downside is the relatively slow refresh rate.

If you have a rooted device, you could try Droid VNC Server (it's on the market). The refresh rate isn't too bad, but I certainly wouldn't want to demo full motion video or an arcade game on it.
You could also get a webcam, rig it up with a tripod. Something like this. Downside is your hands will be in the way, maybe issues with lighting and/or focus. Upside is a decent refresh rate.