技術標籤：kotlinAndroid基礎

預設切換動畫

• MainActivity

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        binding = DataBindingUtil.setContentView(this,R.layout.activity_main)
        binding.viewpager2.adapter = ViewPagerAdapter(this)
        //binding.viewpager2.setPageTransformer(ViewPagerOverlay())
 

    }

• Adapter

package im.zebra.myviewpager2

import androidx.fragment.app.Fragment
import androidx.fragment.app.FragmentActivity
import androidx.viewpager2.adapter.FragmentStateAdapter

class ViewPagerAdapter(fa: FragmentActivity) : FragmentStateAdapter(fa) {

    private val list = arrayOf(
        "微信"
 
,
        "通訊錄",
        "發現",
        "我的"
    )

    override fun getItemCount(): Int = list.size

    override fun createFragment(position: Int): Fragment =
        BlankFragment.newInstance(list[position], "")

}

自定義動畫（縮放）

• binding.viewpager2.setPageTransformer(ViewPagerScale())
  
  

package im.zebra.myviewpager2

import android.view.View
import androidx.viewpager2.widget.ViewPager2
import kotlin.math.abs

private const val MIN_SCALE = 0.75f

class ViewPagerScale : ViewPager2.PageTransformer {

    override fun transformPage(view: View, position: Float) {
        val pageWidth = view.width

        when {
            position < -1 -> { // [-Infinity,-1)
                // This page is way off-screen to the left.
                view.alpha = 0f
            }
            position <= 0 -> { // [-1,0]
                // Use the default slide transition when moving to the left page
                view.alpha = 1F
                view.translationX = 0f
                view.scaleX = 1f
                view.scaleY = 1f
            }
            position <= 1 -> { // (0,1]
                // Fade the page out.
                view.alpha = 1 - position

                // Counteract the default slide transition
                view.translationX = pageWidth * -position

                // Scale the page down (between MIN_SCALE and 1)
                val scaleFactor: Float = (MIN_SCALE
                        + (1 - MIN_SCALE) * (1 - abs(position)))
                view.scaleX = scaleFactor
                view.scaleY = scaleFactor
            }
            else -> { // (1,+Infinity]
                // This page is way off-screen to the right.
                view.alpha = 0f
            }
        }

    }

}

自定義動畫（疊加）

• binding.viewpager2.setPageTransformer(ViewPagerOverlay())
  

package im.zebra.myviewpager2

import android.view.View
import androidx.viewpager2.widget.ViewPager2
import kotlin.math.abs

private const val MIN_SCALE = 1f

class ViewPagerOverlay : ViewPager2.PageTransformer {

    override fun transformPage(view: View, position: Float) {
        val pageWidth = view.width

        when {
            position < -1 -> { // [-Infinity,-1)
                // This page is way off-screen to the left.
                view.alpha = 0f
            }
            position <= 0 -> { // [-1,0]
                // Use the default slide transition when moving to the left page
                view.alpha = 1F
                view.translationX = 0f
                view.scaleX = 1f
                view.scaleY = 1f
            }
            position <= 1 -> { // (0,1]
                // Fade the page out.
                view.alpha = 1 - position

                // Counteract the default slide transition
                view.translationX = pageWidth * -position

                // Scale the page down (between MIN_SCALE and 1)
                val scaleFactor: Float = (MIN_SCALE
                        + (1 - MIN_SCALE) * (1 - abs(position)))
                view.scaleX = scaleFactor
                view.scaleY = scaleFactor
            }
            else -> { // (1,+Infinity]
                // This page is way off-screen to the right.
                view.alpha = 0f
            }
        }

    }

}