Koltin20.Takeout首页顶部渐变效果(6)

最新推荐文章于 2025-05-15 13:08:14 发布

原创最新推荐文章于 2025-05-15 13:08:14 发布 · 177 阅读

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本文介绍了如何在HomeFragment中，通过监听RecyclerView的滑动事件，实现背景透明度随着滑动变化的效果，关键在于监听`onScrolled`方法并实时更新背景颜色。

HomeFragment.dart通过监听RecyclerView的滑动事件来动态啊设置背景的透明度来实现

package com.example.takeout.ui.fragment

import android.app.Fragment
import android.graphics.Color
import android.os.Bundle
import android.util.Log
import android.util.TypedValue
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import androidx.recyclerview.widget.LinearLayoutManager
import androidx.recyclerview.widget.RecyclerView
import com.example.takeout.R
import com.example.takeout.ui.adapter.HomeRvAdapter
import kotlinx.android.synthetic.main.fragment_home.*
import org.jetbrains.anko.find

class HomeFragment : Fragment() {
    lateinit var homeRvAdapter: HomeRvAdapter//延迟初始化
    lateinit var rvHome: RecyclerView

    override fun onCreateView(
        inflater: LayoutInflater,
        container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        val view = View.inflate(activity, R.layout.fragment_home, null)
        rvHome = view.find<RecyclerView>(R.id.rv_home)
        //上下布局
        rvHome.layoutManager = LinearLayoutManager(activity)
        homeRvAdapter = HomeRvAdapter(activity)
        rvHome.adapter = homeRvAdapter

        distance = 120.dp2px()
        return view
    }

    fun Int.dp2px(): Int {
        return TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP,
            toFloat(), resources.displayMetrics).toInt()

    }

    override fun onActivityCreated(savedInstanceState: Bundle?) {
        super.onActivityCreated(savedInstanceState)
        initData()
    }

    val datas: ArrayList<String> = ArrayList<String>()
    var sum: Int = 0
    var distance: Int = 0
    var alpha = 55
    private fun initData() {
        for (i in 0 until 100) {
            datas.add("我是商家：" + i)
        }
        homeRvAdapter.setData(datas)
        //有数据可以滚动才可以监听滚动事件,设置标题的透明效果
        rvHome.setOnScrollListener(object : RecyclerView.OnScrollListener() {

            override fun onScrollStateChanged(recyclerView: RecyclerView, newState: Int) {
                if (recyclerView != null) {
                    super.onScrollStateChanged(recyclerView, newState)
                }
            }

            override fun onScrolled(recyclerView: RecyclerView, dx: Int, dy: Int) {
                if (recyclerView != null) {
                    super.onScrolled(recyclerView, dx, dy)
                }
                sum += dy
                if (sum > distance) {
                    alpha = 255
                } else {
                    alpha = sum * 200 / distance
                    alpha += 55
                }
                Log.e("home", "alpha:$alpha")
                ll_title_container.setBackgroundColor(Color.argb(alpha, 0x31, 0x90, 0xe8))
            }
        })
    }

}

效果如下