一、在onLayout时去改变颜色

/**
 * Created by Yangxy on 2019/6/16
 * description -- 渐变TextView
 */

package com.example.review_source_code_demo.base

import android.annotation.SuppressLint
import android.content.Context
import android.graphics.*
import android.util.AttributeSet
import android.widget.TextView
import com.example.review_source_code_demo.R

/**
 * Created by Yangxy on 2019/6/11
 * description --
 */
class GradientTextView2 @JvmOverloads constructor(
    context: Context,
    attrs: AttributeSet? = null,
    def: Int = 0
) : TextView(context, attrs, def) {
    private var startColor: Int = 0
    private var endColor: Int = 0
    private var gradientMode: String? = null

    init {
        if (attrs != null) {
            val attr = context.obtainStyledAttributes(attrs, R.styleable.GradientTextColor, def, 0)
            startColor = attr.getColor(R.styleable.GradientTextColor_startColor, Color.parseColor("#f5f5f5"))
            endColor = attr.getColor(R.styleable.GradientTextColor_endColor, Color.parseColor("#ff7767"))
            gradientMode = attr.getString(R.styleable.GradientTextColor_gradientMode)
                ?: "horizontal"
            attr.recycle()
        }
    }

    @SuppressLint("DrawAllocation")
    override fun onLayout(changed: Boolean, left: Int, top: Int, right: Int, bottom: Int) {
        super.onLayout(changed, left, top, right, bottom)
        if (changed) {
            if (gradientMode == "vertical") {
                paint.shader = LinearGradient(
                    0f, 0f, 0f, height.toFloat(),
                    startColor,
                    endColor,
                    Shader.TileMode.CLAMP
                )
            } else {
                paint.shader = LinearGradient(
                    0f, 0f, width.toFloat(), 0f,
                    startColor,
                    endColor,
                    Shader.TileMode.CLAMP
                )
            }
        }
    }
}

//attrs文件中加入：
   <!--渐变字的颜色-->
    <declare-styleable name="GradientTextColor">
        <attr name="startColor" format="color" />
        <attr name="endColor" format="color" />
        <attr name="gradientMode" format="string" />
    </declare-styleable>

二、通过自定义onDraw去实现渐变

package com.example.review_source_code_demo.base

import android.content.Context
import android.graphics.*
import android.util.AttributeSet
import android.widget.TextView
import android.graphics.Shader
import android.graphics.LinearGradient
import com.example.review_source_code_demo.R


/**
 * Created by Yangxy on 2019/6/11
 * description --
 */
class GradientColorTextView
@JvmOverloads constructor(
    mContext: Context, attrs: AttributeSet? = null, def: Int = 0
) : TextView(mContext, attrs, def) {

    private var startColor: Int = 0
    private var endColor: Int = 0
    private var mPaint: Paint? = null
    private var mViewWidth: Int = 0
    private var mTextBound: Rect = Rect()
    private var mLinearGradient: LinearGradient? = null

    init {
        if (attrs != null) {
            val a = mContext.obtainStyledAttributes(attrs, R.styleable.GradientTextColor, def, 0)
            startColor = a.getColor(R.styleable.GradientTextColor_startColor, Color.parseColor("#FAD961"))
            endColor = a.getColor(R.styleable.GradientTextColor_endColor, Color.parseColor("#F76B1C"))
            a.recycle()
        }
    }

    override fun onDraw(canvas: Canvas?) {
        mViewWidth = measuredWidth
        mPaint = paint
        val text = text.toString()
        mPaint?.getTextBounds(text, 0, text.length, mTextBound)
        mLinearGradient = LinearGradient(
            0F, 0F, mViewWidth.toFloat(), 0F,
            startColor,
            endColor,
            Shader.TileMode.CLAMP
        )
        mPaint?.shader = mLinearGradient
        canvas?.drawText(
            text,
            (mViewWidth / 2 - mTextBound.width() / 2).toFloat(),
            (measuredHeight / 2 + mTextBound.height() / 2).toFloat(),
            mPaint
        )
    }
}

//attrs文件
   <declare-styleable name="GradientTextColor">
        <attr name="startColor" format="color" />
        <attr name="endColor" format="color" />
    </declare-styleable>

三、重点代码

• 通过Paint的Shader去实现渐变效果

   //横向渐变  
   mLinearGradient = LinearGradient(0F, 0F, mViewWidth.toFloat(), 0F,
              startColor,
              endColor,
              Shader.TileMode.CLAMP)
    //设置paint的shader
    mPaint?.shader = mLinearGradient
  
  
   //纵向渐变  
   mLinearGradient = LinearGradient(0F, 0F, 0F,height.toFloat(), 
              startColor,
              endColor,
              Shader.TileMode.CLAMP)
    //设置paint的shader
    mPaint?.shader = mLinearGradient