原理

定义验证码内容由数字+字母组成 创建一个静态变量包含 ”0-9 a-z“
创建指定大小的bitmap 用于生成画板对象Canvas
使用Random 随机生成 三个255之内的数值 分别代表红 绿 蓝 生成 随机颜色
随机指定文本字体 生成验证码

接着用类似的方法生成 多条随机开始节点 和结束节点 连成的线
返回绘制的Bitmap

效果图

验证码.jpg

代码

class VerificationCodeActivity : AppCompatActivity() {

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

        imageview.setImageBitmap(MyUtils.GetRandomBitmap(300,150))

        imageview.setOnClickListener {
            imageview.setImageBitmap(MyUtils.GetRandomBitmap(300,150))
        }

        btn_ver.setOnClickListener {
            Toast.makeText(this,
                "验证结果 ${MyUtils.MyCurrentRandomString.equals(et_ver.text.toString().trim().toLowerCase())}",
                Toast.LENGTH_LONG).show()
        }

    }

    class MyUtils {
        companion object{
            var MyCurrentRandomString = ""
            val RANDOM_CHARS = "1234567890qwertyuiopasdfghjklzxcvbnm"

            fun GetRandomValdatorString():String{
                var builder = StringBuilder()
                for ( i in 0 until 4){
                    builder.append(RANDOM_CHARS.get( Random().nextInt(RANDOM_CHARS.length)) )
                }
                return builder.toString()
            }

            fun GetRandomBitmap(width:Int , height:Int):Bitmap{
                var myBitmap = Bitmap.createBitmap(width,height,Bitmap.Config.ARGB_8888)
                var myCanvas = Canvas(myBitmap)
                var randomSrtring = GetRandomValdatorString()
                MyCurrentRandomString = randomSrtring
                myCanvas.drawColor(Color.WHITE)
                var myPaint = Paint()
                myPaint.textSize = 50f

                //随机字体颜色
                var color = Color.rgb(Random().nextInt(256),Random().nextInt(256),Random().nextInt(256))
                myPaint.setColor(color)
                //随机字体
                myPaint.isFakeBoldText = Random().nextBoolean()
                myCanvas.drawText(randomSrtring ,
                    (width/2-25* randomSrtring.length/2).toFloat(),
                    (height/2+25 * randomSrtring.length/4).toFloat(), myPaint)
               

                // 绘制干扰线
                for (i in 0..75){
                    var color = Color.rgb(Random().nextInt(256),Random().nextInt(256),Random().nextInt(256))
                    var startX = Random().nextInt(width)
                    var startY = Random().nextInt(height)
                    var stopX = Random().nextInt(width)
                    var stopY = Random().nextInt(height)
                    myPaint.strokeWidth = 1f
                    myPaint.setColor(color)
                    myCanvas.drawLine(startX.toFloat(), startY.toFloat(), stopX.toFloat(),
                        stopY.toFloat() , myPaint)
                }

                return myBitmap
            }
        }
    }
}


<?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:orientation="vertical"
    android:gravity="center_horizontal"
    tools:context=".view200.VerificationCodeActivity">

   <ImageView
       android:id="@+id/imageview"
       android:layout_width="wrap_content"
       android:layout_height="wrap_content"/>


    <EditText
        android:id="@+id/et_ver"
        android:layout_width="300dp"
        android:layout_height="wrap_content"
        android:hint="请输入验证码(不区分大小写)"/>

    <Button
        android:id="@+id/btn_ver"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="开始验证"/>


</LinearLayout>