How to create Android UI library

Question

I have so many util codes for UI and want to create a android library for each of them. With all my research I have done below things.

• File -> new module. Create an android library

• in build.gradle file implement the library implementation project(':app:FirstLibrary')

• Kotlin and xml file in library is below

FirstLib.kt

class FirstLib(mContext: Context) : Activity() {
    private var mContext: Context? = null
    private var view: View? = null

    fun s(message: String?) {
        layoutInflater.inflate(R.layout.first_lib_view, null)
        Toast.makeText(mContext, message, Toast.LENGTH_SHORT).show()
    }
}

first_lib_view.xml 

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

    <TextView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Om Namah Shivaya"
        android:textSize="16sp" />

</LinearLayout>

• Next, I'm trying to access this UI library in main xml file like below

<com.example.firstlibrary.FirstLib
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        tools="ajkdfbj"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

Now I'm not getting anything. Even toast message was not coming.

How to create UI library in Android and use it. I have my own custom video players, audio players, image gradient views etc. I need to make all those libraries now. Thanks for reading

Answer 1

To implement a custom view element you need to put your class into the separate module as you did before and inherit your custom view from a view.

• Ie if it's a custom view and you expect to use it inside xml files then you should create smth like:

MyCustomView @JvmOverloads constructor(
    context: Context, attrs: AttributeSet? = null, defStyleAttr: Int = 0
): View {

// you should override onMeasure, onLayout, onDraw here as it marked as abstract afaik

// and implement your logic

}

and implement the whole onMeasure , onLayout , onDraw logic.

• If you want to extend the existing view logic, then just inherit it from the existing one and hatch behaviour.

MyCustomView @JvmOverloads constructor(
    context: Context, attrs: AttributeSet? = null, defStyleAttr: Int = 0
): TextView() {

... your logic goes here...

} 

You did implement a custom activity but uses it like a view, so, that's why it doesnt work for you

PS:here you can find out more about custom view components