{"id":540,"date":"2021-04-20T05:39:16","date_gmt":"2021-04-20T05:39:16","guid":{"rendered":"http:\/\/meatpie\/?p=540"},"modified":"2021-05-13T04:04:35","modified_gmt":"2021-05-13T04:04:35","slug":"weather-app-convert-to-kotlin","status":"publish","type":"post","link":"https:\/\/snersbots.co.uk\/index.php\/weather-app-convert-to-kotlin\/","title":{"rendered":"Weather App – Convert to Kotlin"},"content":{"rendered":"\n

Starting immediately, all future code needs to be in Kotlin. There is a tag in git, so I know where to go back to if it fails. My student colleague assures me it is simple to convert a Java class to Kotlin. Tomorrow’s job.<\/p>\n\n\n\n

Thanks to my colleague, recently a student, who inspires me with daft ideas like converting my code to Kotlin. It is people like you who keep me young. \u2603\ufe0e<\/p>\n\n\n\n\n\n\n\n

Where we want to be<\/h2>\n\n\n\n

I’ve written enough Java. It is a very standard language – it looks like any other C language, except for the for loops, which seem to differ in every language. You can pretty much google any code snippet you want. There is no more learning to be got from sticking with it, I think.<\/p>\n\n\n\n

My student colleague says Kotlin is the future. Well be that as it may. From where I’m sitting, it might well be that Swift is my future. And Kotlin and Swift seem to share some common philosophies.<\/p>\n\n\n\n

Of course the big difference between Kotlin and Swift is ‘let’ vs ‘val’ for declaring a constant variable. Which makes flipping between languages a little annoying. No matter, that is what IntelliSense’s job is.<\/p>\n\n\n\n

Convert to Kotlin<\/h2>\n\n\n\n

Android Studio very helpfully offers to convert your code for you. Let’s see how it goes.<\/p>\n\n\n\n

\"Screenshot<\/figure><\/div>\n\n\n\n
\"A
Yes Please!<\/figcaption><\/figure><\/div>\n\n\n\n
\"Screenshot
There’s no turning back now!<\/figcaption><\/figure><\/div>\n\n\n\n

After this a lot of Gradle stuff happens. I shall leave it to sort itself out, before the moment of truth when I click the Build button.<\/p>\n\n\n\n

<\/p>\n\n\n\n

Warnings<\/h2>\n\n\n\n

My first warning is a Kotlin version thing:<\/p>\n\n\n\n

Kotlin version that is used for building with Gradle (1.5.0-M2) differs from the one bundled into the IDE plugin (1.4.32)<\/code><\/p>\n\n\n\n

\"Screen
This screenshot in build.gradle<\/figcaption><\/figure><\/div>\n\n\n\n
\"Screenshot
Never seen this page before. Looks more friendly than fixing Gradle files in the code.
DO NOT choose Kotlin.<\/figcaption><\/figure><\/div>\n\n\n\n

Well I give up. I have the latest version of the plugin. And the only Plugin version in the dropdown. <\/p>\n\n\n\n

After all that, it still did not convert my file to Kotlin. So go back and re-convert.<\/p>\n\n\n\n

It created errors on iterators:<\/p>\n\n\n\n

\"Screen
Class ‘kotlin.collections.IntIterator’ is compiled by a pre-release version of Kotlin and cannot be loaded by this version of the compiler<\/figcaption><\/figure><\/div>\n\n\n\n

<\/p>\n\n\n\n

I don’t think we have a gradle issue or a plugin issue. Just a converter issue. <\/p>\n\n\n\n

\"Screenshot
Replace with .. operator seems to do the trick<\/figcaption><\/figure><\/div>\n\n\n\n

There’s probably a more elegant way of doing it, but I have checked for null so should be OK:<\/p>\n\n\n\n

if (null != minutely) {\n    for (minCounter in 0..minutely.size - 1) {\n        if (minutely[minCounter].getWeatherWords().contains(precipType)) {\n            timeTil = minCounter.toLong()\n            break\n        }\n    }\n}<\/pre>\n\n\n\n
Problems<\/h2>\n\n\n\n
I’m fed up. Done it a dozen times. Losing the will to live. I think I might now make my old class into a base class, then inherit a Kotlin class. That way I can pick my fights, instead of trying to get an entire class to compile. <\/p>\n\n\n\n
This helped me: https:\/\/stackoverflow.com\/questions\/43980110\/using-kotlin-class-in-java-cannot-find-symbol<\/a>  At least it helped to produce more helpful errors. <\/p>\n\n\n\n
I’ve finally got it to compile after two days, by clicking every damn suggestion lightbulb, randomly selecting solutions, and then reverting in git.<\/p>\n\n\n\n
Bottom line, my project had so many out of date background things, that Android Studio itself was confused. The trick was persuading the Kotlin gradle version to match the Kotlin plugin version, but without being a gradle guru, it was a bit confusing to put it mildly.<\/p>\n\n\n\n
Fixing Compile Errors<\/h2>\n\n\n\n
\n
Auto-generated failing code:<\/p>\n\n\n\n
for (wordCounter in 0 until weatherWordsJson.length())<\/code><\/p>\n\n\n\n
Fix:<\/p>\n\n\n\n
for (wordCounter in 0..weatherWordsJson.length() - 1)<\/code><\/p>\n\n\n\n
It made all my private properties public – is that right? Well it broke the code. I had to manually change all my properties back to private and add properties. Surely this is not right. Need to find out more.<\/p>\n\n\n\n
IntelliJ<\/h2>\n\n\n\n