效果图

涂鸦.gif

代码

class GraffitiActivity : AppCompatActivity() , View.OnTouchListener{

    // 上一次触摸的位置
    var lastX = 0f
    var lastY = 0f

    // 当前触摸的位置
    var myX = 0f
    var myY = 0f

    lateinit var myCanvas :Canvas
    // 原bitmap
    lateinit var myBitmap : Bitmap
    // 绘制的bitmap
    lateinit var myDrawBitmap : Bitmap
    var myPaint = Paint()


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


        btn1.setOnClickListener {

            // 初始化 图像 画板 画笔 等资源
            myBitmap = BitmapFactory.decodeResource(resources , R.mipmap.bg2)
            myDrawBitmap = Bitmap.createBitmap(myBitmap.width , myBitmap.height , myBitmap.config)
            myCanvas = Canvas(myDrawBitmap)
            myCanvas.drawBitmap(myDrawBitmap , Matrix() , myPaint)
            imageview.setImageBitmap(myDrawBitmap)

            imageview.setOnTouchListener(this)
            myPaint = Paint()
            myPaint.setColor(Color.RED)
            myPaint.strokeWidth = 10f
            myPaint.setXfermode(PorterDuffXfermode(PorterDuff.Mode.CLEAR))
            myCanvas.drawPaint(myPaint)
            myPaint.setXfermode(PorterDuffXfermode(PorterDuff.Mode.SRC))
            myCanvas.drawBitmap(myBitmap,Matrix() , myPaint)
        }



        btn2.setOnClickListener {
            if(myDrawBitmap != null){
                // 保存图片到本地
                var imageUri = contentResolver.insert(MediaStore.Images.Media.EXTERNAL_CONTENT_URI , ContentValues())
                var myOutStream  = contentResolver.openOutputStream(imageUri!!)
                myDrawBitmap.compress(Bitmap.CompressFormat.JPEG , 100 , myOutStream!!)
                Toast.makeText(this,"保存成功",Toast.LENGTH_SHORT).show()
            }
        }

    }



    override fun onTouch(v: View?, event: MotionEvent?): Boolean {
        when(event!!.action){
            MotionEvent.ACTION_DOWN -> {
                lastX = event.x
                lastY = event.y
            }
            MotionEvent.ACTION_UP -> {
                myX = event.x
                myY = event.y
                myCanvas.drawLine(lastX , lastY , myX ,myY , myPaint)
                imageview.invalidate()
            }
            MotionEvent.ACTION_MOVE -> {
                myX = event.x
                myY =event.y
                myCanvas.drawLine(lastX , lastY , myX ,myY , myPaint)
                imageview.invalidate()
                lastX = myX
                lastY = myY
            }
        }

        return true
    }
}



<?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">

    <Button
        android:id="@+id/btn1"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toLeftOf="@id/btn2"
        app:layout_constraintTop_toTopOf="parent"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:text="重新绘制"/>

    <Button
        android:id="@+id/btn2"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintLeft_toRightOf="@id/btn1"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:text="保存图像"/>


    <ImageView
        android:id="@+id/imageview"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        app:layout_constraintTop_toBottomOf="@id/btn1"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        android:scaleType="fitXY"/>

</androidx.constraintlayout.widget.ConstraintLayout>