Android Toast Helper

Toast Helper is a library designed to facilitate the use of Toast notifications while hiding Android dependencies.

Necessity

Although Toasts are frequently used in many apps and screens, they can be challenging to use in layers that aim to exclude framework dependencies, such as MVVM's ViewModel.

For instance, after adding or deleting data in an app, you might use a Toast to notify the user. Typically, to achieve this in a ViewModel, you would define a state or event for the Toast execution and observe it in the UI to handle. However, event-based implementations like SharedFlow risk losing events, and state-based implementations like StateFlow can lead to unintended duplicate processing during reconstructions, such as screen rotations. Therefore, additional measures are needed to prevent these issues.

I find these steps cumbersome and excessive just to execute a Toast. The purpose of this library is to make using Toasts easy.

Installation

Without Framework Dependency

It is a core module without Android dependencies.

implementation("io.github.dylan-kwon:toast-helper-core:$version")

With Android Dependency

It includes an implementation of the core module for actual Toast execution.

implementation("io.github.dylan-kwon:toast-helper-android:$version")

Testing

It includes rules and test components that can be used in testing.

testImplementation("io.github.dylan-kwon:toast-helper-test:$version")

How To Use

Initialization

The Toast helper is automatically initialized using the Jetpack startup.

Disable Auto-Initialization

If you do not want automatic initialization, you can disable it.

manifest.xml

Exclude AndroidToastHelperInitializer during startup initialization.

<provider android:name="androidx.startup.InitializationProvider"
    android:authorities="${applicationId}.androidx-startup" android:exported="false"
    tools:node="merge">
    <meta-data android:name="dylan.kwon.toasthelper.android.startup.AndroidToastHelperInitializer"
        android:value="androidx.startup" tools:node="remove" />
</provider>

Call the setFactory function

ToastHelper.setFactory(
    AndroidToastFactory(applicationContext)
)

In addition to the AndroidToastFactory provided by the library, you can create and set custom objects. For more information on customization, please refer here.

Basic

The basic usage is as follows:

class YourViewModel : ViewModel() {
    ..
    fun somethings() {
        // only message.
        ToastHelper.show("message")

        // message with duration.
        ToastHelper.show("message", ToastDuration.SHORT)
    }
}

Cancel

The displayed Toast can be canceled immediately.

class YourViewModel : ViewModel() {
    ..
    fun somethings() {
        val cancellation = ToastHelper.show("message")

        // To cancel a Toast, call the following.
        cancellation.cancel()
    }
}

Listener

You can attach listeners to the appearance and disappearance of the Toast. The creation and execution of a Toast consist of two steps.

class YourViewModel : ViewModel() {
    ..
    fun somethings() {
        // 1. Create Toast.
        val toast = ToastHelper.create(message).apply {
            addShownCallback {
                // Toast is shown.
            }
            addHiddenCallback {
                // Toast is Hidden. 
            }
        }

        // 2. Show Toast.
        toast.show()
    }
}

Position And Margin

It is possible to specify the position and margin of the Toast.

class YourViewModel : ViewModel() {
    ..
    fun somethings() {
        ToastHelper.show(
            message = "message",
            duration = ToastDuration.SHORT,

            // set position.
            position = ToastPosition(
                gravity = ToastGravity.CLIP_VERTICAL,
                xOffset = 0,
                yOffset = 0
            ),

            // set margin.
            margin = ToastMargin(
                horizontalFraction = 0.5f,  // 0.5 is 50% of screen width.
                verticalFraction = 0.5f     // 0.5 is 50% of screen height.
            )
        )
    }
}

Warning This feature is not supported on Android-R or higher.

Testing

For testing, the following ToastHelperTestRule is provided.

This rule configures the ToastHelper to use println instead of Android Toast in the test environment.

class MyTest {
    @get:Rule
    val rule = ToastHelperTestRule()

    // or
    val rule = ToastHelperTestRule(YourCustomFactory)

    ..

    @Test
    fun test() {
        viewModel.somthings()
    }
}

Output [TOAST][SHORT] Hello World

Custom

Some people might want to modify the behavior of ToastHelper.

For example, in a test environment, it uses println instead of Toast to output in the following format:

println("[TOAST][$durationName] $toastMessage")

Output [TOAST][SHORT] Hello World

If you want to output only the Toast message, configure it as follows:

1. Extend the Toast class to create a custom Toast object.

class YourCustomToast(
    override val message: String,
) : Toast() {

    override fun show(): ToastCancellation {
        println(message)
        return EmptyToastCancellation
    }
}

2. Extend the ToastFactory interface to create a custom factory.

class YourCustomToastFactory : ToastFactory {
    override fun create(
        message: String,
        duration: ToastDuration,
        position: ToastPosition?,
        margin: ToastMargin?
    ): Toast {
        return YourCustomToast(message)
    }
}

3. Set the custom factory in ToastHelper.

ToastHelper.setFactory(yourCustomFactory)

License

This project is licensed under the Apache License, Version 2.0. - see the LICENSE file for details.