kotlinによるアプリケーション開発のエラー(android studio)

Question

最近、kotlinスタートブックを使ってkotliの勉強し始めたのですが、その中のアプリケーションを実際に作成するパートでつまずいています。

ArticleView.kt

package sample.qiitaclient.view

import android.content.Context
import android.graphics.Color
import android.util.AttributeSet
import android.view.LayoutInflater
import android.widget.FrameLayout
import android.widget.ImageView
import android.widget.TextView
import sample.qiitaclient.R
import sample.qiitaclient.model.Article

class ArticleView : FrameLayout {
    constructor(context: Context?) : super(context)

    constructor(context: Context?,
                attrs: AttributeSet?) : super(context, attrs)

    constructor(context: Context?,
                attrs: AttributeSet?,
                defStyleAttr: Int) : super(context, attrs, defStyleAttr)

    /*constructor(context: Context?,
                attrs: AttributeSet?,
                defStyleAttr: Int,
                defStyleRes: Int) : super(context, attrs, defStyleAttr, defStyleRes)*/

    var profileImageView: ImageView? = null

    var titleTextView: TextView? = null

    var userNameTextView: TextView? = null

    init {
        LayoutInflater.from(context).inflate(R.layout.view_article, this)
        **profileImageView = findViewById(R.id.profile_image_view) as ImageView
        titleTextView = findViewById(R.id.title_text_view) as TextView
        userNameTextView = findViewById(R.id.user_name_text_view) as TextView**
    }

    fun setArticle(article: Article) {
        titleTextView?.text = article.title
        userNameTextView?.text = article.user.name

        profileImageView?.setBackgroundColor(Color.RED)
    }
}

build.gradle

apply plugin: 'com.android.application'

apply plugin: 'kotlin-android'

apply plugin: 'kotlin-android-extensions'

android {
    compileSdkVersion 28
    defaultConfig {
        applicationId "sample.qiitaclient"
        minSdkVersion 15
        targetSdkVersion 28
        versionCode 1
        versionName "1.0"
        testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"

    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
        }
    }
}

dependencies {
    implementation fileTree(include: ['*.jar'], dir: 'libs')
    implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk7:$kotlin_version"
    implementation 'com.android.support:appcompat-v7:28.0.0'
    implementation 'com.android.support.constraint:constraint-layout:1.1.3'
    testImplementation 'junit:junit:4.12'
    androidTestImplementation 'com.android.support.test:runner:1.0.2'
    androidTestImplementation 'com.android.support.test.espresso:espresso-core:3.0.2'


}

MainActivity

package sample.qiitaclient.model




import android.support.v7.app.AppCompatActivity
import android.os.Bundle

import sample.qiitaclient.view.ArticleView


class MainActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)

        val articleView = ArticleView(application)

        articleView.setArticle(Article(id = "123",
            title = "Kotlin入門",
            url = "http://www.example.com/articles/123",
            user = User(id = "456", name = "たろう", profileImageUrl = "")))

        setContentView(articleView)
    }
}

ビルドして実行してみると以下のようなエラーが表示されます
Type mismatch: inferred type is Context? but Context was expected
Type mismatch: inferred type is Context? but Context was expected
Type mismatch: inferred type is Context? but Context was expected

Task :app:prepareLintJar UP-TO-DATE
Task :app:generateDebugSources
Task :app:javaPreCompileDebug
Task :app:compileDebugJavaWithJavac
Task :app:instantRunMainApkResourcesDebug
Task :app:mergeDebugShaders UP-TO-DATE
Task :app:compileDebugShaders UP-TO-DATE
Task :app:generateDebugAssets UP-TO-DATE
Task :app:mergeDebugAssets UP-TO-DATE
Task :app:validateSigningDebug UP-TO-DATE
Task :app:signingConfigWriterDebug UP-TO-DATE
Task :app:processInstantRunDebugResourcesApk UP-TO-DATE
Task :app:checkManifestChangesDebug
Task :app:transformClassesWithExtractJarsForDebug UP-TO-DATE

Task :app:transformClassesWithInstantRunVerifierForDebug

Cannot delete /home/yuya/AndroidStudioProjects/QiitaClient/app/build/intermediates/incremental-verifier/debug/android/support/multidex file

Task :app:transformClassesWithDependencyCheckerForDebug
Task :app:compileDebugNdk NO-SOURCE
Task :app:mergeDebugJniLibFolders UP-TO-DATE
Task :app:transformNativeLibsWithMergeJniLibsForDebug
Task :app:processDebugJavaRes NO-SOURCE
Task :app:transformResourcesWithMergeJavaResForDebug
Task :app:transformNativeLibsAndResourcesWithJavaResourcesVerifierForDebug
Task :app:transformClassesWithInstantRunForDebug
Task :app:transformClassesAndClassesEnhancedWithInstantReloadDexForDebug
Task :app:incrementalDebugTasks
Task :app:preColdswapDebug
Task :app:fastDeployDebugExtractor UP-TO-DATE
Task :app:generateDebugInstantRunAppInfo
Task :app:transformClassesWithDexBuilderForDebug
Task :app:transformDexArchiveWithExternalLibsDexMergerForDebug
Task :app:transformDexArchiveWithDexMergerForDebug
Task :app:transformDexWithInstantRunDependenciesApkForDebug

Task :app:instantRunSplitApkResourcesDebug

Time to process all the split resources PT0.361240505S with 2 slaves

Task :app:transformDexWithInstantRunSlicesApkForDebug
Task :app:packageDebug
Task :app:buildInfoGeneratorDebug
Task :app:compileDebugSources
Task :app:assembleDebug

BUILD SUCCESSFUL in 20s
43 actionable tasks: 25 executed, 18 up-to-date

またArticleView.ktのinit{...}の部分のfindViewByIdのところで

Can be converted to findViewById<TextView>(...)

Inspection info: This inspection reports findViewById calls with type casts which can be converted to findViewById with a type parameter from Android 8.0 (API level 26).

というメッセージが表示されます。

わかりにくくて申し訳ありませんが、よろしくおねがいします。

Answer 1

表示されたメッセージをお読みになりましたでしょうか.

context は null 不可なので Context? では無く Context として定義すべきと思います.

constructor(context: Context?) : super(context)

 ↓

constructor(context: Context) : super(context)

findViewById は compileSdkVersion 26 以上では as XXXX では無く <XXXX> と書べきと思います.

profileImageView = findViewById(R.id.profile_image_view) as ImageView

 ↓

profileImageView = findViewById<ImageView>(R.id.profile_image_view)

Comments

[oxyu8]

無事に解決しました。
本当にありがとうございました！