seekBar拖动滑块

中秋节学习，，

通过拖动滑块，改变图片的透明度

<?xml version="1.0" encoding="utf-8"?>

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"

    android:orientation="vertical"

    android:layout_width="match_parent"

    android:layout_height="match_parent">

    <ImageView

        android:id="@+id/image"

        android:layout_width="match_parent"

        android:layout_height="240dp"

        android:src="@drawable/lijiang"/>

    <!-- 定义一个拖动条，并改变它的滑块外观 -->

    <SeekBar

        android:id="@+id/seekbar"

        android:layout_width="match_parent"

        android:layout_height="wrap_content"

        android:max="255"

        android:progress="255"

        android:thumb="@mipmap/ic_launcher"/>

</LinearLayout>

override fun onCreate(savedInstanceState: Bundle?)

    {

        super.onCreate(savedInstanceState)

        setContentView(R.layout.activity_main)

        val image = findViewById<ImageView>(R.id.image)

        val seekBar = findViewById<SeekBar>(R.id.seekbar)

        seekBar.setOnSeekBarChangeListener(object : SeekBar.OnSeekBarChangeListener

        {

            // 当拖动条的滑块位置发生改变时触发该方法

            override fun onProgressChanged(bar: SeekBar, progress: Int, fromUser: Boolean)

            {

                // 动态改变图片的透明度

                image.imageAlpha = progress

            }

            override fun onStartTrackingTouch(bar: SeekBar)

            {

            }

            override fun onStopTrackingTouch(bar: SeekBar)

            {

            }

        })

    }