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创建项目geoquiz
选择EmptyActivity
编程语言选择Kotlin

修改app/src/main/java/MainActivity.kt

package com.bignerdranch.android.geoquiz

import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.view.View
import android.widget.*

class MainActivity : AppCompatActivity() {

    private lateinit var trueButton:Button
    private lateinit var falseButton:Button

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

        trueButton = findViewById(R.id.true_button)
        falseButton = findViewById(R.id.false_button)

        trueButton.setOnClickListener{
            view: View ->
            //do something
            Toast.makeText(this,R.string.correct_toast,Toast.LENGTH_SHORT).show()
        }

        falseButton.setOnClickListener{
            view:View->
            //do somethng
            Toast.makeText(this,R.string.incorrect_toast,Toast.LENGTH_SHORT).show()
        }
    }
}

修改app/src/main/res/layout/activity_main.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:gravity="center"
              android:orientation="vertical" >
    <TextView android:layout_width="wrap_content" android:layout_height="wrap_content"
              android:padding="24dp"
              android:text="@string/question_text" />
    <LinearLayout
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:orientation="horizontal" >

        <Button
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="@string/true_button"
                style="?android:attr/buttonBarButtonStyle"
                android:id="@+id/true_button"/>

        <Button
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="@string/false_button"
                style="?android:attr/buttonBarButtonStyle"
                android:id="@+id/false_button"/>
    </LinearLayout>
</LinearLayout>

修改app/src/main/res/values/strings.xml

<resources>
    <string name="app_name">GeoQuiz</string>
    <string name="question_text">问题1</string>
    <string name="true_button">是</string>
    <string name="false_button">否</string>
    <string name="correct_toast">正确</string>
    <string name="incorrect_toast">错误</string>
</resources>

设置AVD模拟器，运行项目

添加更多的题目

新增app/src/main/java/Question.kt

package com.bignerdranch.android.geoquiz

import androidx.annotation.StringRes

data class Question(@StringRes val textResId:Int,val answer:Boolean)

修改app/src/main/res/layout/activity_main.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"
              xmlns:tools="http://schemas.android.com/tools"
              android:gravity="center"
              android:orientation="vertical">

    <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:padding="24dp"
            android:id="@+id/question_text_view"
            tools:text="@string/question_1"/>
    <LinearLayout
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:orientation="horizontal" >

        <Button
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="@string/true_button"
                style="?android:attr/buttonBarButtonStyle"
                android:id="@+id/true_button"/>

        <Button
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="@string/false_button"
                style="?android:attr/buttonBarButtonStyle"
                android:id="@+id/false_button"/>
    </LinearLayout>

    <Button
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@string/next_button"
            style="?android:attr/buttonBarButtonStyle"
            android:id="@+id/next_button"/>
</LinearLayout>

修改app/src/main/res/values/strings.xml

<resources>
    <string name="app_name">GeoQuiz</string>
    <string name="question_1">问题1</string>
    <string name="question_2">问题2</string>
    <string name="question_3">问题3</string>
    <string name="question_4">问题4</string>
    <string name="next_button">下一题</string>
    <string name="true_button">是</string>
    <string name="false_button">否</string>
    <string name="correct_toast">正确</string>
    <string name="incorrect_toast">错误</string>
</resources>

修改app/src/main/java/MainActivity.kt

package com.bignerdranch.android.geoquiz

import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.view.View
import android.widget.*

class MainActivity : AppCompatActivity() {

    private lateinit var trueButton:Button
    private lateinit var falseButton:Button
    private lateinit var nextButton:Button
    private lateinit var questionTextView: TextView

    private val questionBank = listOf(
        Question(R.string.question_1,true),
        Question(R.string.question_2,false),
        Question(R.string.question_3,true),
        Question(R.string.question_4,false),
    )

    private var currentIndex = 0

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

        trueButton = findViewById(R.id.true_button)
        falseButton = findViewById(R.id.false_button)
        nextButton = findViewById(R.id.next_button)
        questionTextView = findViewById(R.id.question_text_view)

        trueButton.setOnClickListener{
            view: View ->
            //Toast.makeText(this,R.string.correct_toast,Toast.LENGTH_SHORT).show()
            checkAnswer(true)
        }

        falseButton.setOnClickListener{
            view:View->
            //Toast.makeText(this,R.string.incorrect_toast,Toast.LENGTH_SHORT).show()
            checkAnswer(false)
        }

        nextButton.setOnClickListener{
            currentIndex = (currentIndex + 1) % questionBank.size
            updateQuestion()
        }

        updateQuestion()

    }

    private fun updateQuestion(){
        val questionTextResId = questionBank[currentIndex].textResId
        questionTextView.setText(questionTextResId)
    }

    private fun checkAnswer(userAnswer:Boolean){
        val correctAnswer = questionBank[currentIndex].answer
        val messageResId = if(userAnswer == correctAnswer){
            R.string.correct_toast
        }else{
            R.string.incorrect_toast
        }

        Toast.makeText(this,messageResId,Toast.LENGTH_SHORT).show()
    }
}

运行项目

添加图标资源

Activity的生命周期

引入Jetpack库的ViewModel

为什么需要ViewModel

Jetpack库

jetpack官方

一个界面对应一个Activity，下面创建第二个界面，用于显示当前问题的答案

先打开res/values/strings.xml文件,要用的所有字符串资源

<resources>
    <string name="app_name">GeoQuiz</string>
    <string name="question_1">问题1</string>
    <string name="question_2">问题2</string>
    <string name="question_3">问题3</string>
    <string name="question_4">问题4</string>
    <string name="next_button">下一题</string>
    <string name="true_button">是</string>
    <string name="false_button">否</string>
    <string name="correct_toast">正确</string>
    <string name="incorrect_toast">错误</string>

    <string name="warning_text">确认操作吗？</string>
    <string name="show_answer_button">显示答案</string>
    <string name="cheat_button">作弊！</string>
    <stinrg name="judgment_toast">作弊是错误的</stinrg>
</resources>

创建新的activity至少涉及三个文件:Kotlin类文件、XML 布局文件和manifest 文件。这三个文件关联密切，搞错了就有大麻烦。强烈建议使用IDEA的新建 activity向导功能。

Android开发初体验,Android,android

使用向导操作后会自动添加相应的res/layout/activity_cheat.xml文件和app/src/main/java/CheatActivity.kt文件

下面开始构建UI

修改res/layout/activity_cheat.xml文件内容

<?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"
              xmlns:tools="http://schemas.android.com/tools"
              android:gravity="center"
              android:orientation="vertical"
              tools:context=".CheatActivity">

    <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:padding="24dp"
            android:id="@+id/warning_text_view"
            tools:text="@string/warning_text"/>
    <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:padding="24dp"
            android:id="@+id/answer_text_view"
            tools:text="回答"/>
    <Button
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:id="@+id/show_answer_button"
            android:text="@string/show_answer_button"/>
</LinearLayout>

接着检查一下app/main/manifest.xml配置文件中是否声明了 CheatActivity（向导操作默认会有）

内容大概如下

        <activity
                android:name=".CheatActivity"
                android:exported="false"/>

在默认布局中添加作弊!按钮(app/src/main/res/layout/activity_main.xml)

加入如下代码块

    <Button
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@string/cheat_button"
            style="?android:attr/buttonBarButtonStyle"
            android:id="@+id/cheat_button"/>

完整代码如下

<?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"
              xmlns:tools="http://schemas.android.com/tools"
              android:gravity="center"
              android:orientation="vertical">

    <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:padding="24dp"
            android:id="@+id/question_text_view"
            tools:text="@string/question_1"/>
    <LinearLayout
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:orientation="horizontal" >

        <Button
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="@string/true_button"
                style="?android:attr/buttonBarButtonStyle"
                android:id="@+id/true_button"/>

        <Button
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="@string/false_button"
                style="?android:attr/buttonBarButtonStyle"
                android:id="@+id/false_button"/>
    </LinearLayout>

    <Button
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@string/cheat_button"
            style="?android:attr/buttonBarButtonStyle"
            android:id="@+id/cheat_button"/>
    <Button
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@string/next_button"
            style="?android:attr/buttonBarButtonStyle"
            android:id="@+id/next_button"/>
</LinearLayout>

修改MainActivity.kt加入cheatButton的控制处理代码

package com.bignerdranch.android.geoquiz

import android.content.Intent
import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.view.View
import android.widget.*

class MainActivity : AppCompatActivity() {

    private lateinit var trueButton:Button
    private lateinit var falseButton:Button
    private lateinit var nextButton:Button
    private lateinit var cheatButton: Button
    private lateinit var questionTextView: TextView

    private val questionBank = listOf(
        Question(R.string.question_1,true),
        Question(R.string.question_2,false),
        Question(R.string.question_3,true),
        Question(R.string.question_4,false),
    )

    private var currentIndex = 0

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

        trueButton = findViewById(R.id.true_button)
        falseButton = findViewById(R.id.false_button)
        nextButton = findViewById(R.id.next_button)
        cheatButton = findViewById(R.id.cheat_button)
        questionTextView = findViewById(R.id.question_text_view)

        trueButton.setOnClickListener{
            view: View ->
            //Toast.makeText(this,R.string.correct_toast,Toast.LENGTH_SHORT).show()
            checkAnswer(true)
        }

        falseButton.setOnClickListener{
            view:View->
            //Toast.makeText(this,R.string.incorrect_toast,Toast.LENGTH_SHORT).show()
            checkAnswer(false)
        }

        nextButton.setOnClickListener{
            currentIndex = (currentIndex + 1) % questionBank.size
            updateQuestion()
        }

        cheatButton.setOnClickListener{
            //do something
        }

        updateQuestion()

    }

    private fun updateQuestion(){
        val questionTextResId = questionBank[currentIndex].textResId
        questionTextView.setText(questionTextResId)
    }

    private fun checkAnswer(userAnswer:Boolean){
        val correctAnswer = questionBank[currentIndex].answer
        val messageResId = if(userAnswer == correctAnswer){
            R.string.correct_toast
        }else{
            R.string.incorrect_toast
        }

        Toast.makeText(this,messageResId,Toast.LENGTH_SHORT).show()
    }
}

接着来看看如何启动CheatActivity

一个activity启动另一个activity最简单的方式是使用startActivity(Intent)函数

        cheatButton.setOnClickListener{
            val intent = Intent(this,CheatActivity::class.java)
            startActivity(intent)
        }

使用intent extra

在CheatActivity.kt中，为extra数据信息新增键值对中的键

private const val EXTRA_ANSWER_IS_TRUE = "com.bignerdranch.android.geoquiz.answer_is_strue"

CheatActivity.kt代码如下

package com.bignerdranch.android.geoquiz

import android.content.Context
import android.content.Intent
import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle

private const val EXTRA_ANSWER_IS_TRUE = "com.bignerdranch.android.geoquiz.answer_is_strue"

class CheatActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_cheat)
    }

    companion object {
        fun newIntent(packageContext: Context, answerIsTrue: Boolean): Intent {
            return Intent(packageContext,CheatActivity::class.java).apply {
                putExtra(EXTRA_ANSWER_IS_TRUE, answerIsTrue)
            }
        }
    }
}

在MainActivity的按钮监听器中使用newIntent()函数，修改MainActivity.kt文章来源地址https://www.toymoban.com/news/detail-611929.html

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