Question

我想在屏幕上绘制一个自定义视图（一个圆圈）并对其进行操作。但是我想遵循面向对象的范式。能够添加更多的圈子，并使它们也与用户和布局互动。基本上，我希望activity_main是“画布”，并让圆移动并与布局交互。我是Android图形的新手，因此可以使用一些帮助和指导。这是我的代码：

MainActivity：

package com.example.canvasbounds

import android.app.Activity
import android.os.Bundle

class MainActivity : Activity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        val circle= Circle(400f,600f, this)
        circle.invalidate()
    }
}

圆圈：

package com.example.canvasbounds

import android.content.Context
import android.graphics.Canvas
import android.graphics.Color
import android.graphics.Paint
import android.view.View

    class Circle(x: Float, y: Float, context: Context) : View(context) {
        val paint = Paint().apply {
            color = Color.BLUE
            style = Paint.Style.STROKE
            strokeWidth = 8f
        }
        override fun onDraw(canvas: Canvas?) {
            canvas?.drawCircle(x,y,100f,paint)
        }
    }

Answer 1

首先：获取对根布局的引用，例如

R.layout.activity_main就像

<.... ConstraintLayout
    android:id="+@id/container"
    ...>

setContentView之后的活动

val container : ConstraintLayout = findViewById(R.id.container)

第二：要么使用您的默认视图对象

setContentView(R.layout.activity_main)
val container : ConstraintLayout = findViewById(R.id.container)
val circle= Circle(400f,600f, this)
circle.invalidate()
circle.layoutpramas = LayoutParams(25, 25) // for placement on screen,
container.addView(circle)

或者只是添加您就可以在将来创建画布并像这样添加它

setContentView(R.layout.activity_main)
val container : ConstraintLayout = findViewById(R.id.container)
val circle= Circle(400f,600f, this)
circle.invalidate()
circle.layoutpramas = LayoutParams(25, 25) // for placement on screen, different for different layout
container.addView(circle)
val canvas = Canvas()
canvas.drawColor(Color.RED);
circle.draw(canvas)
circle.invalidate()

在布局顶部绘制自定义视图

1 个答案: