Custom View constructor in Android 4.4 crashes on Kotlin, how to fix?

Question

I have a custom view written in Kotlin using JvmOverloads that I could have default value.

class MyView @JvmOverloads constructor(
    context: Context,
    attrs: AttributeSet? = null,
    defStyle: Int = 0,
    defStyleRes: Int = 0
) : LinearLayout(context, attrs, defStyle, defStyleRes)

All works fine in Android 5.1 and above.

However it crashes in 4.4, since the constructor in 4.4 doesn't have defStyleRes. How could I have that supported that in 5.1 and above I could have defStyleRes but not in 4.4, without need to explicitly having 4 constructors defined like we did in Java?

Note: The below would works fine in 4.4, but then we loose the defStyleRes.

class MyView @JvmOverloads constructor(
    context: Context,
    attrs: AttributeSet? = null,
    defStyle: Int = 0
) : LinearLayout(context, attrs, defStyle)

You can read a bit more about the side effects of `@JvmOverloads` in this article: https://medium.com/@mmlodawski/https-medium-com-mmlodawski-do-not-always-trust-jvmoverloads-5251f1ad2cfe — Schadenfreude, Jan 22 '20 at 10:31

Seaskyways · Answer 1 · 2017-07-28T08:17:39.727

15

Best way is to have your class this way.

class MyView : LinearLayout {
    @JvmOverloads constructor(context: Context, attrs: AttributeSet? = null, defStyleAttr: Int = 0) : super(context, attrs, defStyleAttr)
    @TargetApi(Build.VERSION_CODES.LOLLIPOP) constructor(context: Context, attrs: AttributeSet?, defStyleAttr: Int, defStyleRes: Int) : super(context, attrs, defStyleAttr, defStyleRes)
}

edited Jul 28 '17 at 08:17

answered Jul 28 '17 at 05:50

Seaskyways

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That's back to the old way of having all 4 constructors defined :( – Elye Jul 28 '17 at 05:59
Well it's the way Android Works, no matter how much Kotlin's syntax helps, it's Android the one which requires Boilerplate :D Anyways, you can trim these down using default values, but you have to use at least 2 constructors – Seaskyways Jul 28 '17 at 06:03
1

@Elye I have edited my answer to show same functionality with 2 constructors – Seaskyways Jul 28 '17 at 06:10
Hi, that's the same as per what my question is. It will crash in 4.4 – Elye Jul 28 '17 at 06:28
Well of course it will crash if you use the second constructor on 4.4 – Seaskyways Jul 28 '17 at 06:30
Cool. just see your answer. Perhaps would need to wrap with @TargetApi? – Elye Jul 28 '17 at 06:57
1

Yes sure, I will add it. Don't forget to mark it is the correct answer. – Seaskyways Jul 28 '17 at 08:17

score 8 · Answer 2 · answered Jul 28 '17 at 06:56

8

I got a way of doing so. Just overload the first 3 functions will do, leave the 4th one for Lollipop and above wrap with @TargetApi.

class MyView : LinearLayout {
    @JvmOverloads
    constructor(context: Context, attrs: AttributeSet? = null, defStyleAttr: Int = 0)
        : super(context, attrs, defStyleAttr)

    @TargetApi(Build.VERSION_CODES.LOLLIPOP)
    constructor(context: Context, attrs: AttributeSet?, defStyleAttr: Int, defStyleRes: Int)
        : super(context, attrs, defStyleAttr, defStyleRes)
}

answered Jul 28 '17 at 06:56

Elye

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This a valid answer. Good @Elye – raditya gumay Aug 13 '17 at 08:30
How do you access attrs inside the init function with this approach @Elye? – niegus Dec 10 '18 at 15:00
@niegus you can, just make your own `initialize` function al call it – Omar Mainegra Dec 18 '18 at 22:38

score 1 · Answer 3 · answered Dec 04 '18 at 01:35

Just define the constructors like this:

constructor(context: Context) : super(context)
constructor(context: Context, attrs: AttributeSet) : super(context, attrs)
constructor(context: Context, attrs: AttributeSet, defStyleAttr: Int) : super(context, attrs, defStyleAttr)
@TargetApi(21)
constructor(context: Context, attrs: AttributeSet, defStyleAttr: Int, defStyleRes: Int) : super(context, attrs, defStyleAttr, defStyleRes)

Custom View constructor in Android 4.4 crashes on Kotlin, how to fix?

3 Answers3

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