使用Kotlin实现文字渐变TextView的代码

import android.content.Context
import android.graphics.*
import android.support.annotation.ColorInt
import android.support.annotation.ColorRes
import android.text.TextPaint
import android.util.AttributeSet
import android.widget.TextView
import com.ans.utilactivity.R


class GradientTextView @JvmOverloads constructor(
  context: Context?,
  attrs: AttributeSet? = null
) : TextView(context, attrs) {


  private var mPaint: TextPaint? = null
  private var mLinearGradient: LinearGradient? = null
  private var mMeasureWidth = 0
  private var mTextMatrix: Matrix? = null

  @ColorInt
  private var mStartColor: Int = 0xFF333333.toInt()
  @ColorInt
  private var mEndColor: Int = 0xFF333333.toInt()

  init {
    if (attrs != null) {
      val attrArray = getContext().obtainStyledAttributes(attrs, R.styleable.GradientTextView)
      mStartColor = attrArray.getColor(R.styleable.GradientTextView_startColor, mStartColor)
      mEndColor = attrArray.getColor(R.styleable.GradientTextView_endColor, mEndColor)
    }
  }

  /**
   * 复写onSizeChanged方法
   *
   */
  override fun onSizeChanged(w: Int, h: Int, oldw: Int, oldh: Int) {
    super.onSizeChanged(w, h, oldw, oldh)
    mMeasureWidth = measuredWidth
    if (mMeasureWidth   0) {
      mPaint = paint
      //(x0,y0)：渐变起始点坐标
      //(x1,y1):渐变结束点坐标
      //color0:渐变开始点颜色,16进制的颜色表示，必须要带有透明度
      //color1:渐变结束颜色
      //colors:渐变数组
      //positions:位置数组，position的取值范围[0,1],作用是指定某个位置的颜色值，如果传null，渐变就线性变化。
      //tile:用于指定控件区域大于指定的渐变区域时，空白区域的颜色填充方法。
      mLinearGradient = LinearGradient(
        0f
        , 0f
        , mMeasureWidth.toFloat()
        , 0f
        , intArrayOf(mStartColor, mEndColor)
        , null
        , Shader.TileMode.CLAMP
      )
      mPaint?.shader = mLinearGradient
      mTextMatrix = Matrix()
    }
  }
}

<declare-styleable name="GradientTextView" 
  <attr name="startColor" format="color"/ 
  <attr name="endColor" format="color"/ 
</declare-styleable 

<前缀.GradientTextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="Hello World!"
    app:startColor="@color/colorPrimary"
    app:endColor="@color/colorAccent"
    /