app crash on launch

I just finished building a test app, but when i try to run it on my phone by downloading the APK the app just crashes please help.

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see the following general tips and in your case especially #2

1. Use different screens wisely

Before starting to create another screen, first you should think about is it really necessary? See also Building apps with many screens and SteveJG's post about advantages/disadvantages, because in only one screen you also can use vertical arrangements to simulate different screens, just set the arrangements to visible = true/false as needed... See also Martyn_HK's example about how to use Tabs in App Inventor and another example from Cyd. 

The recommended method of switching screens in App Inventor

manager.aia

2. App Inventor works best if you use images whose size matches the size you want them to appear on your screen. If you import larger images into your app, your app may run out of system memory. Using Images with App Inventor

3. Avoid redundancy

Probably it helps to read chapter 19 - 21 in Dave's book http://www.appinventor.org/book2 to get an idea how to do DRY programming with App Inventor - Don't repeat yourself 

4. See SteveJG's monster list of tips and tricks

5. How to overcome the App Inventor project limit of 10 MB

6. Backup your project frequently

to find out more about the Runtime Error, you can use Logcat

I normally use Eclipse and Logcat there, but if you have installed the App InventorSoftware (see also http://appinventor.mit.edu/explore/ai2/setup-emulator.html), you already have everything you need to use logcat...

How to use Logcat

1. connect your device using USB with your computer

2. in File Manager go to the App Inventor directory, which is  C:\Program Files\App Inventor or similar

3. press Shift and right mouse click the subdirectory commands-for-Appinventor to get the context menu

4. select "open command window here" and you will get a command window of that subdirectory

5. enter adb logcat and the logcat will start running

6. start your app to elicit the error

7. copy the log (see below)

To copy your log, right click, click "select all" and enter to copy the complete log into the clipboard, then open Notepad and paste it using ctrl-v.

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