Using MVP - I have a call that returns for instanc...

# announcements

[Joan Colmenero]

Using MVP - I have a call that returns for instance a number between 1-43, then I need to do something like if it's between 1 and 5 show this image, if it's between 6 and 29 another one, so since in Presenter I can't put anything about R and Android context, how do I let the view know which icon has to show? Because as far as I understand view doesn't have to do any logic.
Or for instance, I get a Boolean from API and then from VIEW I want to show an image or another one, I thought about create showWhiteBackground() and showBlackBackground() and then call the correct one, this is ok if the value is between 2, but when it's between 1-43 I can not do something like this 😕

[streetsofboston]

We do emit R.id and R.string, etc from our ViewModels (or Presenters in your case)

[Joan Colmenero]

ViewModels is like a Presenter?

[streetsofboston]

The R constants are just that, constants.
As long as you don’t import Views, Bitmaps, Drawables, Activities, etc into your Presenter source files, it should be good. Those R constants just resolve to plain Integers… even in your tests.

[Joan Colmenero]

But I need to do something like : if it's between 1 and 5 show this image R.drawable.whatever

[streetsofboston]

E.g. in some of our apps, when the MVP wants to show a string in the UI (Activity/Fragment) to which it is attached, we emit an instance of a class of our own called StringResource. Its constructor takes a R.string value and a vararg of arguments.

Then we have a few extension-functions on StringResource somewhere else, tied to the UI, that take a Context or a Fragment or a View to extract a String from that StringResource. E.g. fun Context.getString(stringRes: StringResource) : String = ....

For drawables, colors, etc, we just emit a simple Int, the resource-id

[streetsofboston]

val drawable = when {
   1 <= level and level <= 5 -> R.drawable.level_low
    6 <= level and level <= 10 -> R.drawable.level_mid
    else -> R.drawable.level_hight
}

view.showLevel(drawable)

[Joan Colmenero]

Yes I know, but it is ok to use R in presenter?

[streetsofboston]

Why not, it is just a constant, an Int

[streetsofboston]

Those R constants are not dependent on any Android context/framework. They are auto-generated. Consider them part of your UI-model.

[Joan Colmenero]

Thought I couldn't use R there

[Joan Colmenero]

But let's see if someone can answer tho the question to hear more examples and options

[streetsofboston]

You can. You can use the R constants in your unit-tests as well. Compiles fine 🙂

[Joan Colmenero]

I know it compiles, but it's Anti-pattern to use R.drawable and R.string, at least that's what I understood

[streetsofboston]

To have a translation in your Activity/Fragment from some other set of constants into constants from the R is overkill in my opinion and it adds to much code in your Activities and Fragments that cannot be tested by plain unit-tests.

[streetsofboston]

It’s an anti-pattern to use View, Activity, Drawable, Application, etc that are only defined within an Android context. The R values are generated by the compiler (apt) and are part of your app as plain constants. You could have written those R constants yourself, but the compiler does it for you. 🙂

[Joan Colmenero]

So, if it's this import: import com.name.project.R

[Joan Colmenero]

without Drawable what happens

[streetsofboston]

Do you mean
import com.name.project.R.drawable.*?
This would just import a bunch of Int constants. The drawable here is just a word, has nothing to do with Drawable classes.

[Joan Colmenero]

And what about if I create an Enum which contains the Drawable Int inside?

[Joan Colmenero]

Is that ok?

[streetsofboston]

If you mean by ‘Drawable Int’ the integer constant of a drawable resource, yep, that is fine.
You can wrap them in other classes (enums, data classes, etc) that are part of your UI-model.

[Joan Colmenero]

Something like this I mean

[Joan Colmenero]

enum class Color(val rgb: Int) {
        RED(R.drawable.red),
        GREEN(R.drawable.green),
        BLUE(R.drawable.blue)
}

[streetsofboston]

If that makes your Presenter code more readable, yes, this looks great to me.

[streetsofboston]

I would not call its property rgb, though, since it is not a RGB value. It is a resource-id value.

[Joan Colmenero]

nono, I just changed the values from the documentation

[streetsofboston]

And the enum name is Color, but the values are <http://R.drawable.xxx|R.drawable.xxx> not R.color.xxxx

[Joan Colmenero]

I just modified the things inside of the ENUMS to show the idea

[streetsofboston]

Ah… 🙂 I see, just an example.
Be careful with naming though 🙂

[Joan Colmenero]

So anton, to say a number is between 2 numbers is the way you put?

[Joan Colmenero]

I thought I could use something like in 1..3

[Joan Colmenero]

Something like this :

return when(weatherIcon) {
            in 1..3 -> SomeReturn
            else -> SomeReturn
        }

[streetsofboston]

Yup, that will work.

[Joan Colmenero]

so, if weatherIcon is 1 or 3 should join on the first right?

[Joan Colmenero]

Solved, play.kotlinlang.org is a good tool 😄

[streetsofboston]

Or just put fun main() { .... } in any of your source files and hit the ‘play’ icon shown in the gutter in front of that main function.

[louiscad]

FYI, there's an #android channel.