CODEWITHSUNDEEP
luacoronasdk
user3251969
user3251969

Reputation: 162

Confused about event.type Lua

I'm working from a book and learning about orientation. I'm very confused about the code event.type.

Here's the code from the book:

portrait = display.newText ("Portrait", display.contentWidth / 2,display.contentHeight /      2, nil,20)
portrait: setFillColor ( 1,1,1 )
portrait.alpha = 1

landscape = display.newText ("Landscape", display.contentWidth/ 2, display.contentHeight /2, nil, 20)
landscape: setFillColor (1,1,1)
landscape.alpha = 0

local function onOrientationChange (event)
if (event.type == 'landscapeRight' or event.type == 'landscapeLeft')    then
    local newAngle = landscape.rotation - event.delta
    transition.to (landscape, {time = 1500, rotation = newAngle})
    transition.to (portrait, {rotation = newAngle})
    portrait.alpha = 0
    landscape.alpha = 1
else
    local newAngle = portrait.rotation - event.delta
    transition.to (portrait, {time = 150, rotation = newAngle})
    transition.to (landscape, {rotation = newAngle})
    portrait.alpha = 1
    landscape.alpha = 0
end
end

Seems like the whole orientation change function works around event.type. I don't understand what it is, and I don't understand what it's equal to (==). Further when I change the string(in this case 'landscapeRight' and 'landscapeLeft') that it's equal too. It will take any value and still function okay. I'm completely confused on how it works, please explain event.type.

Upvotes: 1

Views: 154

Answers (2)

Oliver
Oliver

Reputation: 29483

I hope you accept MBlanc's answer, I'm just going to expand here: the orientation event.type is a value that is one of several strings, as indicated on that link in MBlanc's post. Event.type will never be anything other than those strings. So what you are doing by changing the comparison to strings that can never match event.type is ending up in the "else" branch all the time, as though your device was never oriented in landscape:

local function onOrientationChange (event)
    if (event.type == 'blabla1' or event.type == 'blabla2')    then
        ...do stuff -- but will never get run because event.type can never have those values
    else -- so your program always ends up here: 
        ...do other stuff...
    end
end

This will make it appear as though program is running fine except that when your device really is in orientation landscapeRight or left the program will execute the "else" block instead of the block it should have executed (first block).

Upvotes: 1

MBlanc
MBlanc

Reputation: 1783

It is a common Lua idiom to use strings such 'landscapeRight' as enum literals.

For orientation events, event.type holds the new device orientation.

In the code snippet you provided, you don't seem to be calling or otherwise making any reference to onOrientationChange after defining it. You should attach it to the Runtime object using

Runtime:addEventListener('orientation', onOrientationChange)

Upvotes: 2

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