Solution: “Type inference failed” error by using "findViewById” in Kotlin

If you get any error when you are using kotlin and references views to kotlin, then most of time every developer faced  “Type inference failed” error  in Kotlin.

We have few option for such kind of error in kotlin,

var tvName = findViewById(R.id.txtName) as TextView

to

var tvName = findViewById<TextView>(R.id.txtName) 

You can use Kotlin Android Extensions too for that. Check the doc here.

Kotlin Android Extensions:

• In your app gradle.build add apply plugin: 'kotlin-android-extensions'
• In your class add import for import kotlinx.android.synthetic.main.<layout>.* where <layout> is the filename of your layout. for example activity_main
• That's it, you can call TextView directly in your code.

Sometimes its works like this:

var tvName:TextView = findViewById(R.id.txtName) as TextView

If you are using Anko, then you have to do this:

var tvName:TextView = find(R.id.txtName)

Where bind internally work like this:


fun <T : View> Activity.bind(@IdRes res : Int) : T {
    @Suppress("UNCHECKED_CAST")
    return findViewById(res) as T}

More info:
https://kotlinlang.org/docs/tutorials/android-plugin.html
https://blog.jetbrains.com/kotlin/2015/04/announcing-anko-for-android/
https://developer.android.com/sdk/api_diff/26/changes.html

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How to Install Crashlytics via Gradle in Android Studio and Kotlin

Crashlytics is the most powerful, yet lightest weight crash reporting solution.Spend less time finding and more time fixing crashes. Named the #1 performance SDK on both iOS and Android, Crashlytics provides deep and actionable insights, even the exact line of code your app crashed on.

First you have to signup in fabric.io.Then do following steps integrate crashlytics in android using kotlin.

1. Go To build.gradle(Project) and add following dependencies.


2. Go To build.gradle(App) and add following dependencies.


and click sync button on the top:

3. Now, Time to add some fabric key and give internet permission in manifest file



4. Then add following coding snippet in you code, where you want to be add crash.


Now you got email and click view, Then you will get following screen in fabric.io,

Want to know more about installation in android, please visit : fabric.io
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What is new in Android Oreo?

After more than a year of development and months of testing by developers and early adopters (thank you!), we're now ready to officially launch Android 8.0 Oreo to the world. Android 8.0 brings a ton

pic courtesy: developer.android.com

of great features such as picture-in-picture, autofill, integrated Instant Apps, Google Play Protect, faster boot time, and much more.

Make your apps compatible

Test your apps for compatibility with Android Oreo. Just download a device system image, install your current app, and test in areas where behavior changes may affect the app. 

Build for Android Oreo

Target Android Oreo (API 26) and extend your apps with the latest platform capabilities and APIs.      

         
The latest version of Android that’s smarter, faster, and more powerful. Android Oreo gives you many new ways to extend your app and develop more efficiently.

Picture-in-picture

Notification dots

Notification channels

Autofill framework

Autosizing TextView

Fonts in XML

Downloadable fonts

Adaptive icons

Shortcut pinning

Wide-gamut color

WebView features

Java 8 language APIs

Media features

Multidisplay support

More!

More about Oreo, Please visit official android developer website: https://developer.android.com/index.html

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Splash screen in android using KOTLIN

Splash screen in android using kotlin just like java. Thread in java is same as kotlin, we have to make

 thread run certain time and go to next activity( or main activity) .

SpashScreen.Kt



You have to make your own layout as your requirement in activity_splash.xml.

It work just like java splash screen, it will be automatically redirect to MainActivity after 5 second.

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Kotlin 1.1.4-2 is released with new features

Kotlin 1.1.4-2 is just released with several important hotfixes, here are some change logs that kotlin changes in new released version.

1.1.4-2

• KT-19679 CompilationException: Couldn't inline method call 'methodName' into...
• KT-19690 Lazy field in interface default method leads to ClassFormatError
• KT-19716 Quickdoc Ctrl+Q broken while browsing code completion list Ctrl-Space
• KT-19717 Library kind incorrectly detected for vertx-web in Kotlin project
• KT-19723 "Insufficient maximum stack size" during compilation

What feature do we have in kotlin 1.1.4

Android

New Features

• KT-11048 Android Extensions: cannot evaluate expression containing generated properties

Performance Improvements

• KT-10542 Android Extensions: No cache for Views
• KT-18250 Android Extensions: Allow to use SparseArray as a View cache

Fixes

• KT-11051 Android Extensions: completion of generated properties is unclear for ambiguous ids
• KT-14086 Android-extensions not generated using flavors dimension
• KT-14912 Lint: "Code contains STOPSHIP marker" ignores suppress annotation
• KT-15164 Kotlin Lint: problems in delegate expression are not reported
• KT-16934 Android Extensions fails to compile when importing synthetic properties for layouts in other modules
• KT-17641 Problem with Kotlin Android Extensions and Gradle syntax
• KT-17783 Kotlin Lint: quick fixes to add inapplicable @RequiresApi and @SuppressLint make code incompilable
• KT-17786 Kotlin Lint: "Surround with if()" quick fix is not suggested for single expression get()
• KT-17787 Kotlin Lint: "Add @TargetApi" quick fix is not suggested for top level property accessor
• KT-17788 Kotlin Lint: "Surround with if()" quick fix corrupts code in case of destructuring declaration
• KT-17890 [kotlin-android-extensions] Renaming layout file does not rename import
• KT-18012 Kotlin Android Extensions generates @NotNull properties for views present in a configuration and potentially missing in another
• KT-18545 Accessing to synthetic properties on smart casted Android components crashed compiler

Source form kotlin github page: https://github.com/JetBrains/kotlin/tree/1.1.4

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Ad Mob Integration in Kotlin

Firebase is a mobile platform that helps you quickly develop high-quality apps, grow an engaged user base, and earn more money. Since AdMob is now a part of Firebase, we've made it simpler to use AdMob along with other Firebase services such as Analytics.

Here is the simplest way of how to integrate admob in android using kotlin and firebase is very easy.

1. Create a android project in android studio
2. go to tools->Firebase and go to bottom admob details and click first option connect your app to firebase and if you successfully connected then following green ok button appears.

Now click add a banner ad to you app

3. Now click 2nd option ad admob to your app then you got following dialog box and click accept for changes.

and 
4. To put a banner ad in your app, add the following code to your layout file, including the Android Ads schema.


5. Now, you have to load the ad in the activity
Add code to the onCreate() class of this activity to load the ad.

// appId, you can find through the ad mob

MobileAds.initialize(this, resources.getString(R.string.app_id));

// bannar addval adRequest = AdRequest.Builder().build()

adView.loadAd(adRequest)

don't forget to import:

import kotlinx.android.synthetic.main.activity_main.*

6. you have to create ad unit from admob.com and add on string.xml, that has name banner_ad_unit_id.


If you want to add Interstitial Ad, then do following steps,

First you have create Interstitial ad unit in admob and save  interstitial_ad_unit_id  string.xml.

Inside the MainActivity.

internal lateinit var mInterstitialAd: InterstitialAd
internal lateinit var adRequest : AdRequest

want the onCreate method:

mInterstitialAd =  InterstitialAd(this)
mInterstitialAd.setAdUnitId(getString(R.string.interstitial_ad_unit_id));
requestNewInterstitial()

Create function requestNewInterstitial(),

private fun requestNewInterstitial() {
     adRequest = AdRequest.Builder().build()
     mInterstitialAd.loadAd(adRequest)
}

Don't forget to internet permission, otherwise you ad will not displayed in your app.

<uses-permission android:name="android.permission.INTERNET"></uses-permission>

Finally, Inside the button click

if (mInterstitialAd.isLoaded()) {
    mInterstitialAd.show();
} else {
    //go to second activity or do something
}

mInterstitialAd.adListener = object : AdListener() {
    override fun onAdClosed() {
        requestNewInterstitial()
         //go to second activity or do something
    }

    override fun onAdLoaded() {  
    }

    override fun onAdFailedToLoad(i: Int) {
        Log.w("AgeActivity", "onAdFailedToLoad:" + i)
    }
}

Now your both banner ad and  Interstitial Ad both will be displayed , just like screenshot below.

Download and fork project.

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Share Preferences in Kotlin

Interface for accessing and modifying preference data returned by getSharedPreferences(String, int).

You can create a new shared preference file or access an existing one by calling one of two methods:

• getSharedPreferences() — Use this if you need multiple shared preference files identified by name, which you specify with the first parameter. You can call this from any Context in your app.
• getPreferences() — Use this from an Activity if you need to use only one shared preference file for the activity. Because this retrieves a default shared preference file that belongs to the activity, you don't need to supply a name.

Lets to it in kotlin:

First attempt to defined the shared preference and editor then put values on editor and apply for use.

What we have doing in MainActivity:

Now, get the value from shared preference in second activity using key.

Simple we can use for login section, where we can save username, password or remember password for any user.

Here is sample output screenshot:

Download full code and fork

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