If your app does not appear on your device, the most likely problems are:
I'm using wireless and the phone won't connect to the blocks editor.
Try the following steps to troubleshoot your wireless connection.
I installed the MIT AICompanion App before and it doesn't work now.
You must use the latest version of the MIT AICompanion App. If you attempt to use an older version of the Companion App with App Inventor, you will be prompted to update it.
I followed all the wireless instructions and my phone is connected to wifi, and I still cannot connect to App Inventor via wifi.
If you have trouble connecting using these wireless instructions, make sure your phone is using WiFi and not the cell network. On some devices and in some locations, even with WiFi enabled, the phone continues to use the cell network for Internet connectivity. If this is happening to you, you can disable mobile networking (cell phone carrier based Internet connectivity) from your device's Android settings menu. More information about how the wifi connection works.
App Inventor says: You must be connected to the companion or emulator to use "Do It".
This message means that App Inventor believes that it's not connected to any device. If you are using the USB cable, first check that the phone is plugged in. You can also check the connection by using the Connection Test Page. One the phone is connected, stop the Companion software on the phone and try connecting again. If this does not work, or if you are not using USB, try the solution shown under "App Inventor says: Metwork Error Communicating with Companion."
The phone (or emulator) shows a notice -- Security error receiving blocks from browser.
A likely cause for this is that the browser loaded a new project and the Companion didn't recognize that. (Perhaps the phone was unplugged?) Reset the Companion by using the menu key (on the emulator) and select "stop this application". Then reload the browser page, and try connecting again.
The Companion started to run, and then said "Connection error."
This can happen if App Inventor tries to connect and start the companion, and the companion is already running on the device (perhaps from previous project). Go to the running Companion app, press menu, and choose to stop the application. Then try reconnecting again. If this keeps happening, try rebooting the device.
Something you might want to do in the meanwhile is install the setup software and try the emulator... does that work? http://appinventor.mit.edu/explore/ai2/setup-emulator.html
Regards,
Steve
You can use App Inventor without downloading anything to your computer! You'll develop apps on our website: ai2.appinventor.mit.edu. To do live testing on your Android device just install the MIT App Inventor Companion app on your Android phone or tablet. Once the Companion is installed, you can open projects in App Inventor on the web, open the companion on your device, and you can test your apps as you build them:

The following steps will walk you through the process.
Open your device's QR code scanner and scan the QR code on the left below to download the Companion App from the Play Store. If you can't use the Play Store, use the QR code on the right to download the Companion App directly to your phone.
Play StoreRecommended: Automatic updates | APK FileManual updates required |
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Scan this QR code (or click this link) | Scan this QR code (or click this link) |
| If you need a QR code scanner, you can get one at the Play Store (e.g., ZXing). | |
After downloading, step though the the instructions to install the Companion app on your device.You need to install the MIT AI2 Companion only once, and then leave it on your phone or tablet for whenever you use App Inventor.
Note 1: If you are unable to use the QR code, you can still install MIT AI2 Companion on your phone or tablet. Use the Web browser on your device to go to the Google Play Store; look for MIT AI2 Companion in the store. Once you find Companion, click the INSTALL button for the Companion app.
Note 2: If you choose not to go through the Play store and instead load the app directly (aka "side load), you will need to enable an option in your device's settings to allow installation of apps from "unknown sources". To find this setting on versions of Android prior to 4.0, go to "Settings > Applications" and then check the box next to "Unknown Sources". For devices running Android 4.0 or above, go to "Settings > Security" or "Settings > Security & Screen Lock" and then check the box next to "Unknown Sources" and confirm your choice.
App Inventor will automatically show you the app you are building, but only if your computer (running App Inventor) and your Android device (running the Companion) are connected to the same WiFi Network. See a more detailed explanation of this here. Take the time to read what is said on this link; since you last were able to run a Project using WIFI, perhaps something has changed with your WIFI network. Is it possible your phone is attempting to connect to the Internet using a network connection, and not WIFI? You can turn off the network setting on your phone in the Settings.
Some router software require you provide and setup the router password in your Android? Have you done that? Another test, after you are sure your are not using a network connection on your device, connect to the Internet using your device's default brower. Can you surf the Internet? If you cannot, it probably means you phone is not connecting via WIFI to anything.
In the settings in your phone, do you have USB debugging turned on? If so, turn it off. Attempting WIFI and USB at the same time will confuse either AI2 or Companion.
Go to App Inventor and open a project (or create a new one -- use Project > Start New Project and give your project a name). Please create a NEW project; call it JimmyCompanionTest.
Place a button on the Designer Screen. Set the Button.Text to Hello Jimy . That is the entire project. Please do Connect > AI Companion . Does the project load and the button render on your phone?
Then Choose "Connect" and "AI Companion" from the top menu in the AI2 browser:

A dialog with a QR code will appear on your PC screen. On your device, launch the MIT App Companion app just as you would do any app. Then click the “Scan QR code” button on the Companion, and scan the code in the App Inventor window:

Within a few seconds, you should see the app you are building on your device. It will update as you make changes to your design and blocks, a feature called “live testing”.
If you have trouble scanning the QR code or your device does not have a scanner, type the code shown on the computer into the Companion's text area on your Android device exactly as shown. The code is directly below where the screen on your PC shows "Your code is" and consists of six characters. Type the six characters and choose the orange "Connect with code". Do not type an Enter or carriage return: type just the six characters followed by pressing the orange button..
If your app does not appear on your device, the most likely problems are: