如何在 Android Studio 中构建质数检查器 Android 应用程序？

质数是大于1的自然数，它只能被1和它本身整除。前几个素数是： 2 3 5 7 11 13 17 19 23 …… 在本文中，我们将使用Kotlin和 XML 在 Android Studio 中构建一个素数检查器 android 应用程序。应用程序将检查输入的数字是否是质数，如果输入的字是质数，则 Toast 将显示消息“输入的数字是质数”，否则 Toast 的消息将是“输入的字不是质数”质数”。

分步实施

第 1 步：创建一个新项目

要在 Android Studio 中创建新项目，请参阅如何在 Android Studio 中创建/启动新项目。请注意，选择Kotlin作为编程语言。

第 2 步：使用 build.gradle(Module) 文件

您需要像这样在 app build.gradle 模块中应用插件 kotlin-android-extensions

plugins {

   id 'com.android.application'

   id 'kotlin-android'

   id 'kotlin-android-extensions'

}

步骤 3：使用 activity_main.xml 文件

导航到app > res > layout > activity_main.xml并将以下代码添加到该文件中。下面是activity_main.xml文件的代码。

XML

Kotlin

import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.widget.Toast
import androidx.core.text.isDigitsOnly
import kotlinx.android.synthetic.main.activity_main.*
import android.R.bool
import java.lang.Math.sqrt
  
  
class MainActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
  
        // when user clicks on check button.
        check_btn.setOnClickListener {
  
            // check if number_et.text is empty or not
            if (number_et.text.isNotEmpty()) {
  
                // check if et.text is an integer or not.
                if (number_et.text.isDigitsOnly()) {
                    val num = number_et.text.toString().toInt()
                      
                    // check if num is a prime number or not.
                    if (CheckPrime(num)) {
                        Toast.makeText(this, "Entered number is a Prime Number.", Toast.LENGTH_SHORT).show()
                    } else {
                        Toast.makeText(this, "Entered number is a not a Prime Number.", Toast.LENGTH_SHORT).show()
                    }
                }
                // when number_et.text is not an integer value.
                else {
                    Toast.makeText(this, "please enter a valid number.", Toast.LENGTH_SHORT).show()
                }
            }
            // when number_et.text is empty.
            else {
                Toast.makeText(this, "please enter a number", Toast.LENGTH_SHORT).show()
            }
        }
    }
  
    // function to check is a number is prime or not.
    private fun CheckPrime(num: Int): Boolean {
        // Corner case
        if (num <= 1) return false
  
        // Check from 2 to square root of n
        for (i in 2..sqrt(num.toDouble()).toInt()) if (num % i == 0) return false
        return true
    }
  
}

写了这么多代码后，我们的 UI 看起来是这样的：

步骤 4：使用 MainActivity.kt 文件

转到MainActivity.kt文件并参考以下代码。下面是MainActivity.kt文件的代码。代码中添加了注释以更详细地理解代码。

科特林

import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.widget.Toast
import androidx.core.text.isDigitsOnly
import kotlinx.android.synthetic.main.activity_main.*
import android.R.bool
import java.lang.Math.sqrt
  
  
class MainActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
  
        // when user clicks on check button.
        check_btn.setOnClickListener {
  
            // check if number_et.text is empty or not
            if (number_et.text.isNotEmpty()) {
  
                // check if et.text is an integer or not.
                if (number_et.text.isDigitsOnly()) {
                    val num = number_et.text.toString().toInt()
                      
                    // check if num is a prime number or not.
                    if (CheckPrime(num)) {
                        Toast.makeText(this, "Entered number is a Prime Number.", Toast.LENGTH_SHORT).show()
                    } else {
                        Toast.makeText(this, "Entered number is a not a Prime Number.", Toast.LENGTH_SHORT).show()
                    }
                }
                // when number_et.text is not an integer value.
                else {
                    Toast.makeText(this, "please enter a valid number.", Toast.LENGTH_SHORT).show()
                }
            }
            // when number_et.text is empty.
            else {
                Toast.makeText(this, "please enter a number", Toast.LENGTH_SHORT).show()
            }
        }
    }
  
    // function to check is a number is prime or not.
    private fun CheckPrime(num: Int): Boolean {
        // Corner case
        if (num <= 1) return false
  
        // Check from 2 to square root of n
        for (i in 2..sqrt(num.toDouble()).toInt()) if (num % i == 0) return false
        return true
    }
  
}

输出：

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