Konduit - is a React inspired way to bind data to Android Views

Konduit is a layer on top of MVP where a Presenter talks to a View interface. Instead of calling the View interface directly you declare your UI using Widgets and Konduit will inform the View about changes automatically.

In traditional MVP implementations you have to update the View when

• data changes (partially for each change) or
• a new View attaches (orientation change). Having two implementations is hard to maintain and it's nothing new that mutation is the main cause of many problems.

Widgets are immutable data objects which describe the state of a View and provides listeners for user interactions. Each Widget will be bound to the corresponding Android View, a 1:1 mapping. The immutability of the Widgets allows clever diffing and reduces unnecessary updates of the Views.

Instead of calling the View directly you have to implement the build() function which should return a collection of Widgets describing your UI state. The build() function will be automatically called by Konduit when you change the state by calling setState { }. You don't have to worry anymore if your view is currently detached (view == null) causing NullPointerExceptions.

override fun build(context: BuildContext): List<Widget> {
    return widgetList {
    
        text {
            key = R.id.counter_label
            text = "Clicked $count times"
        }

        button {
            key = R.id.increment
            text = if (count == 0) "Click me" else "Increment"
            onClick = onButtonClicked
        }
    }
}

When Konduit detects changes compared to the previous Widgets it will inform the View by calling the single render(List<Widget>) method. This method receives all Widgets at once which is crucial for testing (see later). Konduit then performs a second diff per Widget and binds changed properties to the correct Android View.

The main goal of Konduit was to ease testing. Espresso testing is great, but it requires an Android Emulator. This makes testing slow and flaky.

Konduit allows you write espresso like tests on the JVM.

    @Test
    fun `button click increments`() {
        val ui = MainPresenter().testUi()

        // Given the UI shows the initial state
        assertThat(ui.widget<Text>(R.id.counter_label).text).contains("0")

        // When clicking the increment button
        ui.widget<Button>(R.id.increment).click()

        // Then the counter will be incremented by 1
        assertThat(ui.widget<Text>(R.id.counter_label).text).contains("1")

    }

//TODO add more details

One of the goals of MVP is the separation from the untestable Android Framework allowing us to write JVM test. When it comes to i18n this can be hard to achieve.

//TODO

repositories {
    jcenter()
}

dependencies {
    compile 'com.pascalwelsch.konduit:konduit:0.3.0'
}

See samples

• EditText - Two-way binding of an EditText and i18n
• Alert - Custom Widget and dynamic View
• RecyclerView - ListsWidget with click listener bound to custom RecyclerView.Adapter
• Options Menu - Options menu with Widgets / manual binding

Copyright 2018 Pascal Welsch

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

   http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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