Android MiniPaint App 添加清除选项以清除 Canvas

Question

无法添加清除选项以清除 Canvas。

尝试添加：

有趣的 clear(){ extraCanvas.drawColor(backgroundColor) path.reset() extraBitmap.eraseColor(backgroundColor) invalidate() }

在 MainActivity onOptionsItemSelected 方法中初始化 clear() function 它。 但是 clear() function 没有触发 onOptionsItemSelected 中的大多数触发位。

我的完整代码

MainActivity.kt

class MainActivity：AppCompatActivity（）{

 private val paintView: MyCanvasView? = null override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) val myCanvasView = MyCanvasView(this)

// myCanvasView.systemUiVisibility = SYSTEM_UI_FLAG_FULLSCREEN

 myCanvasView.contentDescription = getString(R.string.canvasContentDescription) setContentView(myCanvasView) } override fun onCreateOptionsMenu(menu: Menu?): Boolean { val inflater: MenuInflater = menuInflater inflater.inflate(R.menu.menu, menu) return super.onCreateOptionsMenu(menu) } override fun onOptionsItemSelected(item: MenuItem): Boolean { return when (item.itemId) { R.id.clear -> { paintView?.clear()

Toast.makeText(this, "Cleared",Toast.LENGTH_LONG).show() return true }

 else -> super.onOptionsItemSelected(item) } return true }

}

MyCanvasView.kt

import android.content.Context
import android.graphics.*
import android.view.MotionEvent
import android.view.View
import android.view.ViewConfiguration
import androidx.core.content.res.ResourcesCompat

private const val STROKE_WIDTH = 12f

class MyCanvasView(context: Context) : View(context) {



    private lateinit var extraCanvas: Canvas
    private lateinit var extraBitmap: Bitmap

    private val backgroundColor = ResourcesCompat.getColor(resources, R.color.colorBackground, null)
    private val drawColor = ResourcesCompat.getColor(resources, R.color.colorPaint, null)


    private val paint = Paint().apply {


        color = drawColor
        // Smooths out edges of what is drawn without affecting shape.
        isAntiAlias = true
        // Dithering affects how colors with higher-precision than the device are down-sampled.
        isDither = true
        style = Paint.Style.STROKE // default: FILL
        strokeJoin = Paint.Join.ROUND // default: MITER
        strokeCap = Paint.Cap.ROUND // default: BUTT
        strokeWidth = STROKE_WIDTH // default: Hairline-width (really thin)
    }

    private var path = Path()

    private var motionTouchEventX = 0f
    private var motionTouchEventY = 0f
    private var currentX = 0f
    private var currentY = 0f


    private val touchTolerance = ViewConfiguration.get(context).scaledTouchSlop
    private lateinit var frame: Rect

    override fun onSizeChanged(width: Int, height: Int, oldWidth: Int, oldHeight: Int) {
        super.onSizeChanged(width, height, oldWidth, oldHeight)
        if (::extraBitmap.isInitialized) extraBitmap.recycle()
        extraBitmap = Bitmap.createBitmap(width, height, Bitmap.Config.ARGB_8888)
        extraCanvas = Canvas(extraBitmap)
        extraCanvas.drawColor(backgroundColor)
// Calculate a rectangular frame around the picture.
        val inset = 40
        frame = Rect(inset, inset, width - inset, height - inset)

    }

    override fun onDraw(canvas: Canvas?) {
        super.onDraw(canvas)
        canvas?.drawBitmap(extraBitmap, 0f, 0f, null)
        canvas?.drawRect(frame, paint)

    }

    private fun touchStart() {
        path.reset()
        path.moveTo(motionTouchEventX, motionTouchEventY)
        currentX = motionTouchEventX
        currentY = motionTouchEventY
    }

    private fun touchMove() {
        val dx = Math.abs(motionTouchEventX - currentX)
        val dy = Math.abs(motionTouchEventY - currentY)
        if (dx >= touchTolerance || dy >= touchTolerance) {
            // QuadTo() adds a quadratic bezier from the last point,
            // approaching control point (x1,y1), and ending at (x2,y2).
            path.quadTo(
                currentX,
                currentY,
                (motionTouchEventX + currentX) / 2,
                (motionTouchEventY + currentY) / 2
            )
            currentX = motionTouchEventX
            currentY = motionTouchEventY
            // Draw the path in the extra bitmap to cache it.
            extraCanvas.drawPath(path, paint)
        }
        invalidate()
    }

    private fun touchUp() {
        path.reset()
//        clear()
    }

    override fun onTouchEvent(event: MotionEvent): Boolean {

        motionTouchEventX = event.x

        motionTouchEventY = event.y

        when (event.action) {
            MotionEvent.ACTION_DOWN -> touchStart()
            MotionEvent.ACTION_MOVE -> touchMove()
            MotionEvent.ACTION_UP -> touchUp()
        }
        return true
    }

    fun clear() {
        extraCanvas.drawColor(backgroundColor)
        path.reset()
        extraBitmap.eraseColor(backgroundColor)
        invalidate()


    }