Chris Greenhalgh (cmg@cs.nott.ac.uk) 1

Google AppInventor implementation quickstart

Chris GreenhalghG54UBI / 2011-03-03

Chris Greenhalgh (cmg@cs.nott.ac.uk) 2

Implementation stages: design-led application-development

1. Create a new application2. Create rough versions of the screens and screen elements 3. Implement basic navigation4. Define domain model types (if used)5. Define application (internal) state (e.g. global vars)6. Create helper functions to update UI7. Add sensor input (from test app)8. Add complex UI elements9. Complete/refine logic10. Tidy up layout, content and look and feel

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1. Create a new application

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Log into App Inventorhttp://appinventor.googlelabs.com

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Notes

• You’ll need to create a google account if you don’t already have one

• To log in you might have to explicitly enable cookies for– google.com– googlelabs.com

• E.g. for Windows/Internet explorer, Control panel >> Internet options >> Privacy >> Sites, Allow…

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Create a project

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The new project…

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2. Create rough versions of the screens and screen elements

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Add a vertical arrangement for each “screen”

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Notes

• AppInventor currently only allows an application to have one “screen”– = Android “activity”

• But can create the effect of multiple screens by hiding/showing groups of elements– In this case the “vertical arrangements”

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Create main elements and add to “screens”

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Notes

• Clicking the “picture” property of an image allows you to add (i.e. upload) an image file– PNG, JPG

• Rename… the components so that you can identify them later by name only– E.g. “WelcomeScreen”, “WelcomeButton”

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3. Implement basic navigation

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Open the blocks editor…

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Notes

Allow the application to run:

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…find (e.g.) the WelcomeButton under “My Blocks” and drag the “when … .Click” onto the

canvas…

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…and then (e.g.) the WelcomeScreen “set … Visible” into the “when … .Click” gap…

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…from “Built in”, “Logic” drag “false” into the gap in “set … to”…

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Try running it…

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Notes

• If “Connect to device” reports “No available device” then click “New emulator” first

• The emulator may take a minute or two to start– “unlock” it when it has

• It may take a minute or so to connect; the app should then appear

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Try clicking on start…

The Welcome screenPart should disappear!

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Notes

• Now go back to the editor and uncheck “visible” for all “screens” except the WelcomeScreen – They will then be hidden when the app starts– Press “Connect to Device” again to re-start the app

• In the blocks editor make “when WelcomeButton.Click” also do “set MainScreen.Visible to” “true”

• Repeat for other navigation buttons and screens

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Notes

• You add temporary buttons to the UI to fake sensor input at this stage if you want to be able to check out sensor-driven navigation

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4. Define domain model types (if used)– AppInventor doesn’t really support a domain

model – no op

5. Define application (internal) state (e.g. global vars)– Nothing much at the moment…

6. Create helper functions to update UI– GPS update might be the only contender here

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7. Add sensor input

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Add a (invisible) location sensor

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Notes

• Add a label to the main view for test output of latitude and longitude, e.g.

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Simulating GPS in the emulator (1)

• Use a terminal program such as telnet to connect to the emulator – Emulator port is in

corner of emulator window (5554)

• One of the supported commands is “geo nmea ….”

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Simulating GPS in the emulator (2)

http://www.cs.nott.ac.uk/~cmg/nmeagenerator/index.html

• A few programs will generate NMEA strings– i.e. the data from a GPS

receiver

• Or you can log real GPS data

• Past the strings into the emulator console…

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Simulating GPS in the emulator (3)

• The emulator now thinks it has a GPS lock and fires a GPS location update event

• Note: location accuracy is not simulated – Appears perfectly

accurate

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Work out the trigger regions…

• E.g. http://www.mrl.nott.ac.uk/~txl/zoneauthor– A HTML/JS browser app to author polygonal zones

and generate KML

Long,lat pairs

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• Code region test logic on location change• …

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8. Add complex UI elements9. Complete/refine logic10.Tidy up layout, content and look and feel