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@manyou

【Android初心者】intent で画面遷移ができない...setContentViewを理解していないことが失敗の原因

Last updated at Posted at 2020-03-10

Androidアプリ開発の教科書Kotlin対応 を参考にAndroidのアプリについて勉強しています
7章 画面遷移とIntentクラス ではまった
はまっていた当時のコード

概要.png

目的の動作は上記の絵の通り。
ビルドは問題なくできているのに、、、

「から揚げ定食」を押した際のlogcatを見てみると、たくさんのエラーが、、、、 logcat
結果的に以下のエラーを読んだことが修正のきっかけになりました。

    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.masashi.things.intentsample/com.masashi.things.intentsample.MenuThanksActivity}: 
java.lang.IllegalStateException: tvMenuPrice must not be null

遷移したい先の「MenuThanksActivity」が見つからないみたい。。。
遷移したい先の「tvMenuPrice」がnullになっていることが原因で、「MenuThanksActivity」がスタートできないって言ってます。
※エラーの解釈について@linsks_2_3_4 さんからコメントをいただきました。
ありがとうございます！
https://qiita.com/manyou/items/1bce375100a11fc614b0#comment-4a7cb04c63f16065227e

MenuThanksActivity.kt を見てみると、以下のような文を発見

public class MenuThanksActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

MenuThanksActivity.kt を以下のように修正したら。。。。成功！！わーーい！！ 

public class MenuThanksActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_menu_thanks)  #ここを変更！

setContentView は 引数に画面のレイアウトが書かれた~~~.xmlを指定するのだね、、、（笑）
超基本そう。。。

        setContentView(R.layout.activity_menu_thanks)

↓↓↓↓↓ 以下は詳細 ↓↓↓↓↓

#logcat

I/System.out: masashi, から揚げ定食
W/ActivityThread: handleWindowVisibility: no activity for token android.os.BinderProxy@bae3899
I/System.out: masashimasashimasashi
W/masashi: masashi
I/System.out: masashi,800円
D/AndroidRuntime: Shutting down VM
E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.masashi.things.intentsample, PID: 19030
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.masashi.things.intentsample/com.masashi.things.intentsample.MenuThanksActivity}: java.lang.IllegalStateException: tvMenuPrice must not be null
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3270)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3409)
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:83)
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2016)
        at android.os.Handler.dispatchMessage(Handler.java:107)
        at android.os.Looper.loop(Looper.java:214)
        at android.app.ActivityThread.main(ActivityThread.java:7356)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930)
     Caused by: java.lang.IllegalStateException: tvMenuPrice must not be null
        at com.masashi.things.intentsample.MenuThanksActivity.onCreate(MenuThanksActivity.kt:28)
        at android.app.Activity.performCreate(Activity.java:7802)
        at android.app.Activity.performCreate(Activity.java:7791)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1299)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3245)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3409) 
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:83) 
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135) 
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2016) 
        at android.os.Handler.dispatchMessage(Handler.java:107) 
        at android.os.Looper.loop(Looper.java:214) 
        at android.app.ActivityThread.main(ActivityThread.java:7356) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930) 

#code

  • activity_main.xml
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity">

<ListView
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/lvMenu"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    tools:ignore="MissingConstraints" />


</androidx.constraintlayout.widget.ConstraintLayout>
  • AndroidManifest.xml
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.masashi.things.intentsample">

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity android:name=".MenuThanksActivity"></activity>
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>
  • activity_main.xml
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity">

<ListView
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/lvMenu"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    tools:ignore="MissingConstraints" />


</androidx.constraintlayout.widget.ConstraintLayout>
  • activity_menu_thanks.xml
<?xml version="1.0" encoding="utf-8"?>

<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:layout_marginBottom="10dp"
    android:gravity="center"
    android:text="@string/tv_thx_title"
    android:textSize="25sp"/>

<TextView
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_marginBottom="10dp"
    android:text="@string/tv_thx_desc"
    android:textSize="15sp"/>

<LinearLayout
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:orientation="horizontal">

    <TextView
        android:id="@+id/tvMenuName"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_weight="1"
        android:orientation="horizontal"/>

    <TextView
        android:id="@+id/tvMenuPrice"
        android:layout_width="243dp"
        android:layout_height="wrap_content" />

</LinearLayout>

<Button
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:onClick="onBackButtonClick"
    android:text="@string/bt_thx_back"/>
</LinearLayout>
  • strings.xml
<resources>
    <string name="app_name">画面遷移サンプル</string>
    <string name="tv_thx_title">注文完了</string>
    <string name="tv_thx_desc">以下のメニューのご注文を受け付けました\nご注文ありがとうございます。</string>
    <string name="bt_thx_back">リストに戻る</string>
</resources>
  • MenuThanksActivity.kt
package com.masashi.things.intentsample

import android.nfc.Tag
import android.os.Bundle
import android.util.Log
import android.view.View
import android.widget.TextView
import androidx.appcompat.app.AppCompatActivity
import com.masashi.things.intentsample.R
import kotlinx.android.synthetic.main.activity_menu_thanks.*


public class MenuThanksActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        val menuName = intent.getStringExtra("menuName")
        val menuPrice = intent.getStringExtra("menuPrice")
        //val tvMenuName = findViewById<TextView>(R.id.tvMenuName)
        val tvMenuName = findViewById<TextView>(R.id.tvMenuName)
        val tvMenuPrice = findViewById<TextView>(R.id.tvMenuPrice)

        println("masashimasashimasashi")
        Log.w("masashi","masashi")
        println("masashi,$menuPrice")
        //TextViewに定食と金額を表示
        tvMenuPrice.text = menuPrice
        //tvMenuPrice.setText(String.valueOf(menuPrice))
        tvMenuName.text=menuName
    }
    fun onBackButtonClick(view: View) {
        Log.w("masashi","masashi")
        finish()
    }
}
  • MainActivity.kt
package com.masashi.things.intentsample

import android.content.Intent
import android.net.sip.SipSession
import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.view.View
import android.widget.AdapterView
import android.widget.ListView
import android.widget.SimpleAdapter
import androidx.core.content.ContextCompat.startActivity

class MainActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        val lvMenu = findViewById<ListView>(R.id.lvMenu)
        val menuList: MutableList<MutableMap<String, String>> = mutableListOf()
        //から揚げ定食のデータを格納するMapオブジェクトの用意とmenuListへのデータ登録
        var menu = mutableMapOf("name" to "から揚げ定食", "price" to "800円")
        menuList.add(menu)
        menu = mutableMapOf("name" to "ハンバーグ定食", "price" to "850円")
        menuList.add(menu)


        val from = arrayOf("name", "price")
        val to = intArrayOf(android.R.id.text1, android.R.id.text2)
        //SimpleAdapterを生成
        val adapter = SimpleAdapter(applicationContext, menuList, android.R.layout.simple_list_item_2, from, to)
        lvMenu.adapter = adapter


        lvMenu.onItemClickListener = ListItemClickListener()
    }

    private inner class ListItemClickListener : AdapterView.OnItemClickListener {
        override fun onItemClick(parent: AdapterView<*>, view: View, position: Int, id: Long) {
            val item = parent.getItemAtPosition(position) as MutableMap<String, String>
            //定食名と金額を取得
            val menuName = item["name"]
            val menuPrice = item["price"]
            //intent オブジェクトを生成
            val intent = Intent(applicationContext, MenuThanksActivity::class.java)
            //第二画面に送るデータを格納
            intent.putExtra("menuName", menuName)
            intent.putExtra("menuPrice", menuPrice)
            println("masashi, $menuName")
            //第二画面の起動
            startActivity(intent)
        }

    }
}
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