android - 在布局之上绘制自定义 View

Question

我想在屏幕上绘制一个自定义 View ，一个圆圈并对其进行操作。但是我想遵循面向对象的范例；能够添加更多圈子并让它们也与用户和布局进行交互。基本上，我希望 activity_main 成为“ Canvas ”并让圆圈移动并与布局交互。我是 android 图形的新手，所以我可以使用一些帮助和指导。这是我的代码:

主要 Activity :

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()
    }
}

圈子:

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"
    ...>

在 setContentView 之后的 Activity 中

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

第二:要么使用你的默认 View 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)

或者只是添加你可以在未来创建一个 Canvas 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()