android - 如何为绘图/素描创建自定义视图（画布），可以像在 Evernote 应用程序中一样在任何方向上无限滚动/拖动

Question

我想构建一个绘图应用程序，用户可以在其中绘制用户想要的任何东西，我可以在屏幕大小的画布上绘制，我想为用户提供一个像 Evernote 应用程序这样的功能，用户可以通过拖动在任何方向上绘制帆布。我创建了一个自定义视图，可以在向下滚动时增加高度。但问题是它在滚动时闪烁很多。这里只是一个视图示例，任何帮助将不胜感激。提前致谢。

class DrawingSheet : View, View.OnTouchListener, GestureDetector.OnGestureListener {

private var mLastWidth: Int = 0
private var mLastHeight: Int = 0
private var mBrushStartX: Float = 0f
private var mBrushStartY: Float = 0f
private var mBrushEndX: Float = 0f
private var mBrushEndY: Float = 0f
private var gesture: GestureDetector? = null
private val mCanvas: Canvas = Canvas()

private val mDefaultBrushPaint = Paint().apply {
    color = Color.RED
}

init {

    minimumWidth = context.resources.displayMetrics.widthPixels
    minimumHeight = context.resources.displayMetrics.heightPixels
    mLastWidth = minimumWidth
    mLastHeight = minimumHeight * 2


    gesture = GestureDetector(context, this)
}

constructor(context: Context) : super(context)

constructor(context: Context, attributeSet: AttributeSet) : super(context, attributeSet)

override fun onDraw(canvas: Canvas?) {
    super.onDraw(canvas)
    canvas?.drawColor(Color.WHITE)
    canvas?.drawLine(mBrushStartX, mBrushStartY, mBrushEndX, mBrushEndY, mDefaultBrushPaint)

    canvas?.drawCircle(100f, 100f, 200f, mDefaultBrushPaint)

    canvas?.drawCircle(600f, 900f, 200f, mDefaultBrushPaint)
    canvas?.drawCircle(1000f, 1900f, 200f, mDefaultBrushPaint)
    canvas?.drawCircle(1500f, 2900f, 200f, mDefaultBrushPaint)

    var x = 0f
    var y = 0f

    while (y < height) {
        canvas?.drawLine(x, y, width.toFloat(), y, mDefaultBrushPaint)
        y += 100
    }

    /*x = 0f
    y = 0f

    while (x < width) {
        canvas?.drawLine(x, y, x, height.toFloat(), mDefaultBrushPaint)
        x += 100
    }*/


}

override fun onMeasure(widthMeasureSpec: Int, heightMeasureSpec: Int) {
    super.onMeasure(widthMeasureSpec, heightMeasureSpec)
    println("onMeasure")
    setMeasuredDimension(mLastWidth, mLastHeight)
}

@SuppressLint("ClickableViewAccessibility")
override fun onTouchEvent(event: MotionEvent?): Boolean {
    return  gesture?.onTouchEvent(event)!!
}

override fun onSizeChanged(w: Int, h: Int, oldw: Int, oldh: Int) {
    super.onSizeChanged(w, h, oldw, oldh)
}
override fun onDown(event: MotionEvent?): Boolean {
    println("onDown")

    return true
}

override fun onShowPress(e: MotionEvent?) {
    println("onShowPress")

}

override fun onSingleTapUp(e: MotionEvent?): Boolean {
    println("onSingleTapUp")
    return true
}

override fun onScroll(
    e1: MotionEvent?,
    e2: MotionEvent?,
    distanceX: Float,
    distanceY: Float
): Boolean {
    println("onScroll")
    println(y)
    println(distanceY)
    println("y + height:  ${y + height}")

    if (y + height < 2500) {
        updateLayoutParams {
            height += minimumHeight
        }
        mLastHeight = layoutParams.height
        mLastWidth = layoutParams.width
    }
    x -= distanceX
    y -= distanceY



    return true
}



override fun onLongPress(e: MotionEvent?) {

}

override fun onFling(
    e1: MotionEvent?,
    e2: MotionEvent?,
    velocityX: Float,
    velocityY: Float
): Boolean {
   
    return true
}

}

标签： androidcanvasdrawing