如何跨越多个活动

Question

我需要帮助从一项活动转移到另一项活动。我是一个初学者，只是学习如何使用Kotlin来构建应用程序。

因此，我的项目包含大约14个活动，当我分别单击“继续”或“ Back”按钮时，我需要能够从一个活动转移到另一个活动和向后移动。

我已经能够使用“意图”从主要活动导航到第二个活动，

但是，当我尝试从第二个活动转到第三个活动时，该应用程序不断将我返回MainAttivity .....和如果我再次这样做，那就崩溃了。

这是我的主攻击代码；

package com.example.mywaterlow02

import android.content.Intent
import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.widget.Button

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

        val buttonStart: Button = findViewById(R.id.button_start)
        buttonStart.setOnClickListener {
            val intentMain = Intent (this, GenderPg::class.java)
            startActivity(intentMain)

        }

    }
}

...这是第二个活动代码

package com.example.mywaterlow02

import android.content.Intent
import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.widget.Button

class GenderPg : AppCompatActivity() {

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

        val genderBack : Button = findViewById(R.id.btn_gender_back)
        genderBack.setOnClickListener {
            val intentGender = Intent (this, MainActivity::class.java)
            startActivity(intentGender)
        }

        val genderContinue : Button = findViewById(R.id.btn_gender_continue)
        genderContinue.setOnClickListener {
            val intentGender2 = Intent (this, AgePg02::class.java)
            startActivity(intentGender2)
        }

    }
}

，这是第三个活动代码

package com.example.mywaterlow02

import android.content.Intent
import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.widget.Button

class AgePg02 : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_age_pg02)

        val ageBack : Button = findViewById(R.id.age_back)
        ageBack.setOnClickListener {
            val intentAge01 = Intent (this, GenderPg::class.java)
            startActivity(intentAge01)
        }

        val ageContinue : Button = findViewById(R.id.age_continue)
        ageContinue.setOnClickListener {
            val intentAge02 = Intent (this, BmiPg02::class.java)
            startActivity(intentAge02)
        }

    }
}

androidManifest XML

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.mywaterlow02">

    <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/Theme.MaterialComponents.DayNight.NoActionBar">
        <activity
            android:name=".BmiPg02"
            android:exported="false" />
        <activity
            android:name=".AgePg02"
            android:exported="false" />
        <activity
            android:name=".GenderPg"
            android:exported="false" />
        <activity
            android:name=".MainActivity"
            android:exported="true">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

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

        <meta-data
            android:name="preloaded_fonts"
            android:resource="@array/preloaded_fonts" />
    </application>

</manifest>

MainActivity XML

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 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"
    android:background="@color/Primary"
    android:gravity="center_horizontal"
    android:orientation="vertical"
    tools:context=".MainActivity">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="250dp"
        android:fontFamily="@font/courier_prime_bold"
        android:text="WATERLOW"
        android:textSize="60sp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:fontFamily="@font/courier_prime_bold"
        android:text="Calculator"
        android:textSize="45sp"/>

    <Button
        android:id="@+id/button_start"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginLeft="40sp"
        android:layout_marginTop="50dp"
        android:layout_marginRight="40sp"
        android:height="70dp"
        android:backgroundTint="@color/Secondary"
        android:fontFamily="@font/courier_prime_bold"
        android:text="Start"
        android:textColor="@color/white"
        android:textSize="25sp" />
</LinearLayout>

第二活动XML

<?xml version="1.0" encoding="utf-8"?>
<ScrollView 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"
    android:background="@color/Primary"
    android:fillViewport="true"
    tools:context=".GenderPg">

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical"
        android:padding="16dp">

        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:fontFamily="@font/courier_prime_bold"
            android:text="Gender"
            android:layout_marginTop="100sp"
            android:layout_marginStart="18sp"
            android:textSize="35sp"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintLeft_toLeftOf="parent"
            app:layout_constraintRight_toRightOf="parent"
            app:layout_constraintTop_toTopOf="parent" />

        <TextView
            android:id="@+id/gender_female"
            android:layout_width="match_parent"
            android:layout_height="60dp"
            android:layout_marginStart="16dp"
            android:layout_marginTop="35dp"
            android:layout_marginEnd="16dp"
            android:layout_marginBottom="10dp"
            android:fontFamily="@font/courier_prime_bold"
            android:background="@drawable/shadowy_bckgrd"
            android:padding="20dp"
            android:paddingStart="25dp"
            android:textColor="#7A8089"
            android:textSize="18sp"
            android:text="@string/female"
            tools:text="Female"
            />

        <TextView
            android:id="@+id/gender_male"
            android:layout_width="match_parent"
            android:layout_height="60dp"
            android:layout_marginStart="16dp"
            android:layout_marginTop="10dp"
            android:layout_marginEnd="16dp"
            android:layout_marginBottom="10dp"
            android:background="@drawable/shadowy_bckgrd"
            android:fontFamily="@font/courier_prime_bold"
            android:padding="15dp"
            android:paddingStart="25dp"
            android:textColor="#7A8089"
            android:textSize="18sp"
            android:text="@string/male"
            tools:text="Male" />

        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="160dp"
            android:layout_marginTop="-10dp"
            android:orientation="horizontal">

            <com.google.android.material.button.MaterialButton
                android:id="@+id/btn_gender_back"
                style="@style/Widget.MaterialComponents.Button.OutlinedButton"
                android:layout_width="145dp"
                android:layout_height="75dp"
                android:layout_marginStart="22dp"
                android:layout_marginTop="30dp"
                android:layout_marginEnd="10dp"
                android:height="70dp"
                android:fontFamily="@font/courier_prime_bold"
                android:text="Back"
                android:textColor="@color/black"
                android:textSize="20dp"
                app:cornerRadius="5dp"
                app:strokeColor="@color/black"
                app:strokeWidth="1dp"
                android:textAllCaps="false"/>

            <Button
                android:id="@+id/btn_gender_continue"
                android:layout_width="145dp"
                android:layout_height="75dp"
                android:layout_marginHorizontal="31dp"
                android:layout_marginStart="38dp"
                android:layout_marginTop="30dp"
                android:height="70dp"
                android:backgroundTint="@color/Secondary"
                android:fontFamily="@font/courier_prime_bold"
                android:text="Continue"
                android:textColor="@color/white"
                android:textSize="20sp"
                android:textAllCaps="false"/>

        </LinearLayout>


    </LinearLayout>

</ScrollView>

第三活动XML

<?xml version="1.0" encoding="utf-8"?>
<ScrollView 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"
    android:background="@color/Primary"
    android:fillViewport="true"
    tools:context=".AgePg02">

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical"
        android:padding="16dp">

        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:fontFamily="@font/courier_prime_bold"
            android:text="Age"
            android:layout_marginTop="100sp"
            android:layout_marginStart="35sp"
            android:textSize="35sp"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintLeft_toLeftOf="parent"
            app:layout_constraintRight_toRightOf="parent"
            app:layout_constraintTop_toTopOf="parent" />

        <TextView
            android:id="@id/age_back"
            android:layout_width="300dp"
            android:layout_height="60dp"
            android:layout_marginStart="35dp"
            android:layout_marginTop="35dp"
            android:layout_marginEnd="10dp"
            android:layout_marginBottom="10dp"
            android:fontFamily="@font/courier_prime_bold"
            android:background="@drawable/shadowy_bckgrd"
            android:padding="20dp"
            android:paddingStart="25dp"
            android:textColor="#7A8089"
            android:textSize="18sp"
            android:text="@string/_14_49"
            tools:text="14 - 49"
            />

        <TextView
            android:id="@+id/age_5064"
            android:layout_width="300dp"
            android:layout_height="60dp"
            android:layout_marginStart="35dp"
            android:layout_marginTop="5dp"
            android:layout_marginEnd="10dp"
            android:layout_marginBottom="10dp"
            android:background="@drawable/shadowy_bckgrd"
            android:fontFamily="@font/courier_prime_bold"
            android:padding="15dp"
            android:paddingStart="25dp"
            android:textColor="#7A8089"
            android:textSize="18sp"
            android:text="@string/_50_to_64"
            tools:text="50 - 64" />

        <TextView
            android:id="@+id/age_6574"
            android:layout_width="300dp"
            android:layout_height="60dp"
            android:layout_marginStart="35dp"
            android:layout_marginTop="5dp"
            android:layout_marginEnd="10dp"
            android:layout_marginBottom="10dp"
            android:background="@drawable/shadowy_bckgrd"
            android:fontFamily="@font/courier_prime_bold"
            android:padding="15dp"
            android:paddingStart="25dp"
            android:textColor="#7A8089"
            android:textSize="18sp"
            tools:text="65 - 74" />

        <TextView
            android:id="@+id/age_7580"
            android:layout_width="300dp"
            android:layout_height="60dp"
            android:layout_marginStart="35dp"
            android:layout_marginTop="5dp"
            android:layout_marginEnd="10dp"
            android:layout_marginBottom="10dp"
            android:background="@drawable/shadowy_bckgrd"
            android:fontFamily="@font/courier_prime_bold"
            android:padding="15dp"
            android:paddingStart="25dp"
            android:textColor="#7A8089"
            android:textSize="18sp"
            android:text="@string/_75_to_80"
            tools:text="75 - 80" />

        <TextView
            android:id="@+id/age_81plus"
            android:layout_width="300dp"
            android:layout_height="60dp"
            android:layout_marginStart="35dp"
            android:layout_marginTop="5dp"
            android:layout_marginEnd="10dp"
            android:layout_marginBottom="10dp"
            android:background="@drawable/shadowy_bckgrd"
            android:fontFamily="@font/courier_prime_bold"
            android:padding="15dp"
            android:paddingStart="25dp"
            android:textColor="#7A8089"
            android:textSize="18sp"
            android:text="@string/over_81"
            tools:text="81+" />

        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="160dp"
            android:layout_marginTop="-10dp"
            android:orientation="horizontal">

            <com.google.android.material.button.MaterialButton
                android:id="@+id/age_back"
                style="@style/Widget.MaterialComponents.Button.OutlinedButton"
                android:layout_width="140dp"
                android:layout_height="75dp"
                android:layout_marginStart="40dp"
                android:layout_marginTop="50dp"
                android:layout_marginEnd="10dp"
                android:height="70dp"
                android:fontFamily="@font/courier_prime_bold"
                android:text="Back"
                android:textColor="@color/black"
                android:textSize="18dp"
                android:textAllCaps="false"
                app:cornerRadius="5dp"
                app:strokeColor="@color/black"
                app:strokeWidth="1dp" />

            <Button
                android:id="@+id/age_continue"
                android:layout_width="140dp"
                android:layout_height="75dp"
                android:layout_marginTop="50dp"
                android:height="70dp"
                android:backgroundTint="@color/Secondary"
                android:fontFamily="@font/courier_prime_bold"
                android:text="Continue"
                android:textAllCaps="false"
                android:textColor="@color/white"
                android:textSize="18dp" />

        </LinearLayout>

    </LinearLayout>

</ScrollView>

我在做什么错？.....为什么我不能从第二个活动转到第三个活动活动？

这是我在logcat中看到的错误消息……我不知道如何修复它或它的含义..

2022-05-06 08:53:02.992 12622-12622/com.example.mywaterlow02 E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.mywaterlow02, PID: 12622
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.mywaterlow02/com.example.mywaterlow02.AgePg02}: java.lang.ClassCastException: com.google.android.material.textview.MaterialTextView cannot be cast to android.widget.Button
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3635)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3792)
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:103)
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2210)
        at android.os.Handler.dispatchMessage(Handler.java:106)
        at android.os.Looper.loopOnce(Looper.java:201)
        at android.os.Looper.loop(Looper.java:288)
        at android.app.ActivityThread.main(ActivityThread.java:7839)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:548)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1003)
     Caused by: java.lang.ClassCastException: com.google.android.material.textview.MaterialTextView cannot be cast to android.widget.Button
        at com.example.mywaterlow02.AgePg02.onCreate(AgePg02.kt:13)
        at android.app.Activity.performCreate(Activity.java:8051)
        at android.app.Activity.performCreate(Activity.java:8031)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1329)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3608)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3792) 
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:103) 
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135) 
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2210) 
        at android.os.Handler.dispatchMessage(Handler.java:106) 
        at android.os.Looper.loopOnce(Looper.java:201) 
        at android.os.Looper.loop(Looper.java:288) 
        at android.app.ActivityThread.main(ActivityThread.java:7839) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:548) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1003) 

请我该怎么办？

Answer 1

Activity agepg02开始启动，但

Caused by: java.lang.ClassCastException: com.google.android.material.textview.MaterialTextView cannot be cast to android.widget.Button

在increate（）中崩溃。

原因是该活动在您的布局XML文件中，您具有button和a textView，并带有此ID：

android:id="@id/age_back"

Answer 2

看来@ID/age_back是一个文本视图，您正在尝试将其施加到第三个活动中的按钮，在线行val ageback：button = button = findViewById（r.id.age_back）。

您可以将TextView更改为第三个活动XML 中的按钮，也可以使用Val Ageback：TextView = FindViewById（R.Id.age_back）更正该行。