Android Kotlin制作签名白板并保存图片

package dem.vaccae.signnatureview

import android.content.Context
import android.graphics.*
import android.util.AttributeSet
import android.view.MotionEvent
import android.view.View
import androidx.core.view.drawToBitmap
import java.lang.Float.max
import kotlin.math.min

class SignatureView(context: Context?, attrs: AttributeSet?) : View(context, attrs) {

    //笔划宽度
    private var STROKE_WIDTH = 5f

    private var lastTouchX = -1f
    private var lastTouchY = -1f

    //定义画笔相关
    private val paint = Paint()

    //定义画笔路径
    private val path = Path()

    //绘制的矩形区域
    private val drawRect = RectF()

    //初始化数据
    init {
        //设置抗锯齿
        paint.isAntiAlias = true
        //设置画笔颜色
        paint.color = Color.BLUE
        //设置画笔类型
        paint.style = Paint.Style.STROKE
        //设置画笔的线冒样式
        paint.strokeCap = Paint.Cap.ROUND
        //设置画笔连接处样式
        paint.strokeJoin = Paint.Join.ROUND
        //设置画笔宽度
        paint.strokeWidth = STROKE_WIDTH
    }

    //清除绘制
    fun clear(){
        path.reset()
        postInvalidate()
    }

    //获取当前页面图片
    fun getBitmapFromView():Bitmap{
        return drawToBitmap()
    }

    //设置笔划宽度
    fun setPaintStrokeWidth(width:Float){
        STROKE_WIDTH = width
        paint.strokeWidth = STROKE_WIDTH
    }

    //设置笔划宽度
    fun setPaintColor(color: Int){
        paint.color = color
    }

    //画笔手执处理
    override fun onTouchEvent(event: MotionEvent?): Boolean {
        event?.let {
            val event_x = it.x
            val event_y = it.y

            when (it.action) {
                MotionEvent.ACTION_DOWN -> {
                    //点击按下时开始记录路径
                    path.moveTo(event_x, event_y)
                    //记录最后的X和Y的坐标
                    lastTouchX = event_x
                    lastTouchY = event_y

                    return true
                }
                MotionEvent.ACTION_MOVE, MotionEvent.ACTION_UP -> {
                    //计算绘制区域
                    drawRect.left = min(lastTouchX, event_x)
                    drawRect.right = max(lastTouchX, event_x)
                    drawRect.top = min(lastTouchY, event_y)
                    drawRect.bottom = max(lastTouchY, event_y)

                    // 当硬件跟踪事件的速度快于事件的交付速度时
                    // 事件将包含这些跳过点的历史记录
                    val historySize = it.historySize
                    (0 until historySize).forEach { i ->
                        val historicalx = it.getHistoricalX(i)
                        val historicaly = it.getHistoricalY(i)
                        if (historicalx < drawRect.left) {
                            drawRect.left = historicalx
                        } else if (historicalx > drawRect.right) {
                            drawRect.right = historicalx
                        }

                        if (historicaly < drawRect.top) {
                            drawRect.top = historicaly
                        } else if (historicaly > drawRect.bottom) {
                            drawRect.bottom = historicaly
                        }

                        path.lineTo(historicalx, historicaly)
                    }

                    // 回放历史记录后，将线路连接到触点。
                    path.lineTo(event_x, event_y)
                }
                else -> {
                    return false
                }
            }

            // 绘制时根据笔画宽度除2用于在中心开妈绘制
            postInvalidate(
                (drawRect.left - STROKE_WIDTH / 2).toInt(),
                (drawRect.top - STROKE_WIDTH / 2).toInt(),
                (drawRect.right + STROKE_WIDTH / 2).toInt(),
                (drawRect.bottom + STROKE_WIDTH / 2).toInt()
            );

            lastTouchX = event_x;
            lastTouchY = event_y;
        }
        return super.onTouchEvent(event)
    }


    override fun onDraw(canvas: Canvas?) {
        canvas?.let {
            it.drawPath(path, paint)
        }
        super.onDraw(canvas)
    }

}

<?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">


    <dem.vaccae.signnatureview.SignatureView
        android:layout_width="match_parent"
        android:layout_height="400dp"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        android:id="@+id/signatureView" />


    <ImageView
        android:layout_width="200dp"
        android:layout_height="150dp"
        android:id="@+id/imgv"
        android:layout_marginTop="20dp"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@id/signatureView" />

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/btnclear"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@id/imgv"
        app:layout_constraintEnd_toStartOf="@id/btnSave"
        android:text="清除" />

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/btnSave"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintStart_toEndOf="@id/btnclear"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintTop_toBottomOf="@id/imgv"
        android:text="保存图片" />

</androidx.constraintlayout.widget.ConstraintLayout>

package dem.vaccae.signnatureview

import android.graphics.Color
import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.widget.ImageView
import android.widget.Toast
import dem.vaccae.signnatureview.databinding.ActivityMainBinding
import kotlin.random.Random

class MainActivity : AppCompatActivity() {

    private lateinit var binding: ActivityMainBinding

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

        binding = ActivityMainBinding.inflate(layoutInflater)
        setContentView(binding.root)

        binding.signatureView.setBackgroundColor(Color.rgb(245,245,245))

        binding.btnclear.setOnClickListener {
            binding.signatureView.clear()
        }

        binding.btnSave.setOnClickListener {
            val bmp = binding.signatureView.getBitmapFromView()
            binding.imgv.scaleType = ImageView.ScaleType.FIT_XY
            binding.imgv.setImageBitmap(bmp)
        }
    }
}