Android画布Canvas绘制手指MotionEvent.ACTION_MOVE 事件矩形方框，Kotlin

 

 

import android.content.Context
import android.graphics.Canvas
import android.graphics.Color
import android.graphics.Paint
import android.graphics.Rect
import android.os.Bundle
import android.util.AttributeSet
import android.view.MotionEvent
import androidx.appcompat.app.AppCompatActivity
import androidx.appcompat.widget.AppCompatImageView


class MainActivity : AppCompatActivity() {
    private var image: MyImage? = null

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        image = findViewById(R.id.image)
    }
}

class MyImage : AppCompatImageView {
    private var curX: Float? = 0f
    private var curY: Float? = 0f

    private var mIsDraw = false

    constructor(ctx: Context, attrs: AttributeSet) : super(ctx, attrs) {

    }

    override fun onTouchEvent(event: MotionEvent?): Boolean {
        when (event?.actionMasked) {
            MotionEvent.ACTION_DOWN -> {
                mIsDraw = true
            }

            MotionEvent.ACTION_MOVE -> {
                curX = event?.x
                curY = event?.y

                invalidate()
            }

            MotionEvent.ACTION_UP -> {
                mIsDraw = false
            }
        }

        return true
    }

    override fun draw(canvas: Canvas) {
        super.draw(canvas)

        if (mIsDraw) {
            myDraw(canvas)
        }
    }

    private fun myDraw(canvas: Canvas) {
        val paint = Paint(Paint.ANTI_ALIAS_FLAG)
        paint.color = Color.RED
        paint.style = Paint.Style.STROKE
        paint.strokeWidth = 40f

        val w = 400
        val h = 300
        val rect = Rect((curX!! - w / 2).toInt(), (curY!! - h / 2).toInt(), (curX!! + w / 2).toInt(), (curY!! + h / 2).toInt())

        canvas.drawRect(rect, paint) //在这块区域边框绘制线。
    }
}

 

手指在屏幕上移动，红色方框跟随手指的位置移动，手指接触屏幕的位置为红色方框的中心：

 

 

 

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