图片随手指移动 --自定义控件--onTouchEvent

• 前言
• 一、思路？
• 二、完整代码

写一个可以随手指移动而移动的图片，用自定义view实现，重写onTouchEvent方法

①：定义两个偏移量作为绘制图片时的起始位置

    private var offsetX = 0f
    private var offsetY = 0f

②：按下时记录手指的位置
声明

private var downX = 0f
private var downY = 0f

记录

            MotionEvent.ACTION_DOWN -> {
                downX = event.x
                downY = event.y
            }

③：第二次移动时先移动到生成结束时的位置
声明

    private var originOffsetX = 0f
    private var originOffsetY = 0f

④：移动

            MotionEvent.ACTION_MOVE -> {
                offsetX = event.x - downX + originOffsetX
                offsetY = event.y - downY + originOffsetY
                invalidate()
            }

用目前手指移动后的位置减去按下时手指的位置，在加上上次图片的位置

package com.lbj23.customview.customview

import android.content.Context
import android.graphics.Canvas
import android.graphics.Paint
import android.util.AttributeSet
import android.view.MotionEvent
import android.view.View
import com.lbj23.customview.R
import com.lbj23.customview.dp
import com.lbj23.customview.getAvatar

class MovingImage(context: Context?, attrs: AttributeSet?) : View(context, attrs) {
    private val image = getAvatar(resources, R.drawable.bg6, 85.dp.toInt())
    private var offsetX = 0f
    private var offsetY = 0f
    private var originOffsetX = 0f
    private var originOffsetY = 0f
    private var downX = 0f
    private var downY = 0f
    private val paint = Paint(Paint.ANTI_ALIAS_FLAG)
    override fun onDraw(canvas: Canvas) {
        super.onDraw(canvas)
        canvas.drawBitmap(image, offsetX, offsetY, paint)
    }

    override fun onTouchEvent(event: MotionEvent): Boolean {
        when (event.action) {
            MotionEvent.ACTION_DOWN -> {
                downX = event.x
                downY = event.y
                originOffsetX = offsetX
                originOffsetY = offsetY
            }
            MotionEvent.ACTION_MOVE -> {
                offsetX = event.x - downX + originOffsetX
                offsetY = event.y - downY + originOffsetY
                invalidate()
            }
        }
        return true
    }
}