xml 仅缩放视图内容的ViewGroup - 实际测量的尺寸保持不变

Posted 2021-05-16

package de.jskierbi.commons.ui

import android.content.Context
import android.util.AttributeSet
import android.view.ViewGroup
import de.neofonie.meinwerder.R

/**
 * Created by jakub on 10.10.17.
 */
class ContentScaleView @JvmOverloads constructor(context: Context,
                                                 attrs: AttributeSet? = null,
                                                 defStyleAttr: Int = 0) : ViewGroup(context, attrs, defStyleAttr) {

  private val contentScale: Float

  init {
    val a = context.obtainStyledAttributes(attrs, R.styleable.ContentScaleView, defStyleAttr, 0)
    contentScale = a.getFloat(R.styleable.ContentScaleView_contentScale, 1f)
    a.recycle()
  }

  override fun onMeasure(widthMeasureSpec: Int, heightMeasureSpec: Int) {
    super.onMeasure(widthMeasureSpec, heightMeasureSpec)
    val contentWidth = (measuredWidth / contentScale).toInt()
    val contentHeight = (measuredHeight / contentScale).toInt()
    val childWidthSpec = MeasureSpec.makeMeasureSpec(contentWidth, MeasureSpec.EXACTLY)
    val childHeightSpec = MeasureSpec.makeMeasureSpec(contentHeight, MeasureSpec.EXACTLY)
    (0 until childCount).forEach {
      val child = getChildAt(it)
      child.measure(childWidthSpec, childHeightSpec)
      child.scaleX = contentScale
      child.scaleY = contentScale
    }
  }

  override fun onLayout(changed: Boolean, left: Int, top: Int, right: Int, bottom: Int) {
    if (!changed) return

    val width = (right - left)
    val height = (bottom - top)

    val expectedWidth = width / contentScale
    val expectedHeight = height / contentScale

    val widthDiff = ((expectedWidth - width) / 2).toInt()
    val heightDiff = ((expectedHeight - height) / 2).toInt()

    (0 until childCount).forEach {
      val child = getChildAt(it)
      child.layout(
        0 - widthDiff,
        0 - heightDiff,
        width + widthDiff,
        height + heightDiff
      )
    }
  }
}

</resources>    
  <attr name="contentScale" format="float" />
  <declare-styleable name="ContentScaleView">
    <attr name="contentScale" />
  </declare-styleable>
</resources>