1.背景

万恶的设计小姐姐又来搞事情啦，你说好好的设计一个纯色的背景框框不好嘛，非要把一个框框弄成渐变的，如果不拿出放大镜估计没几个人能看出来它是渐变的。来，我让你看看是啥样


框子是从左到右渐变的，设计应该是做了一个底图，然后上面盖了一个白色圆角矩形。那么我们该怎么去实现它呢？

实现方法

下面介绍三种实现它的方法。先贴上源码地址，大家记得给个star

https://github.com/stramChen/AndroidGradientBorderDrawable.git

1.利用PorterDuffXfermode进行图层的混合，这是最推荐的方法，也是最有效的。

关于图形混合不明白的，推荐看下面的文章
https://blog.csdn.net/iispring/article/details/50472485

实现思路大致就是先在canvas上绘制一个渐变的圆角矩形，然后再利用clear混合模式在原矩形中间绘制一个较小的圆角矩形将中间的颜色擦除，即中间绘制的颜色和原颜色会混合成透明色，这样就能达到渐变框框的效果了，是不是很容易。废话不多说，直接上代码。

/**
 * @des: 渐变背景边框
 * @author: 569133338@qq.com
 * @date: 2023/2/23 16:19
 */
public class BorderDrawable extends Drawable {
   public int mLeftBorderWidth = 0;
   public int mRightBorderWidth = 0;
   public int mTopBorderWidth = 0;
   public int mBottomBorderWidth = 0;

   public float mBorderRadius =0;

   public float[] mBorderRadii;

   Path mOuterPath = new Path();
   Path mInnerPath = new Path();

   private Paint mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);

   private Shader mShader;

   private int mColor;

   private int[] mColors;

   private Integer mWidth;

   private Integer mHeight;

   private RectF mRectF;

   public BorderDrawable(int borderWidth) {
      this(borderWidth,borderWidth,borderWidth,borderWidth);
   }

   public void setCornerRadii(@Nullable float[] radii) {
      this.mBorderRadii = radii;
   }

   public void setCornerRadius(float radius) {
      this.mBorderRadius = radius;
   }

   public void setColor(int color){
      mColor = color;
      mPaint.setColor(mColor);
   }

   public void setColors(int[] colors){
      mColors = colors;
   }

   public BorderDrawable(int leftBorderWidth, int rightBorderWidth, int topBorderWidth, int bottomBorderWidth) {
      mLeftBorderWidth = leftBorderWidth;
      mRightBorderWidth = rightBorderWidth;
      mTopBorderWidth = topBorderWidth;
      mBottomBorderWidth = bottomBorderWidth;
   }


   @Override
   public void draw(Canvas canvas) {
      int width = getBounds().width();
      int height = getBounds().height();
      if(mWidth == null || mHeight == null || mWidth != width || mHeight != height){
         mOuterPath.reset();
         mInnerPath.reset();
         if(Build.VERSION.SDK_INT >= 21){
            if(mBorderRadii != null){
               mOuterPath.addRoundRect(0,0,width,height,mBorderRadii, Path.Direction.CW);
               mInnerPath.addRoundRect(mLeftBorderWidth,mTopBorderWidth,width-mRightBorderWidth,height-mBottomBorderWidth,mBorderRadii, Path.Direction.CW);
            }else {
               mOuterPath.addRoundRect(0,0,width,height,mBorderRadius,mBorderRadius, Path.Direction.CW);
               mInnerPath.addRoundRect(mLeftBorderWidth,mTopBorderWidth,width-mRightBorderWidth,height-mBottomBorderWidth,mBorderRadius,mBorderRadius, Path.Direction.CW);
            }
         }else {
            if(mBorderRadii != null){
               mOuterPath.addRoundRect(new RectF(0,0,width,height),mBorderRadii, Path.Direction.CW);
               mInnerPath.addRoundRect(new RectF(mLeftBorderWidth,mTopBorderWidth,width-mRightBorderWidth,height-mBottomBorderWidth),mBorderRadii, Path.Direction.CW);
            }else {
               mOuterPath.addRoundRect(new RectF(0,0,width,height),mBorderRadius,mBorderRadius, Path.Direction.CW);
               mInnerPath.addRoundRect(new RectF(mLeftBorderWidth,mTopBorderWidth,width-mRightBorderWidth,height-mBottomBorderWidth),mBorderRadius,mBorderRadius, Path.Direction.CW);
            }
         }

         if(null != mColors){
            mShader = new LinearGradient(0, 0, width, 0,
                    mColors, null, Shader.TileMode.REPEAT);
            mPaint.setShader(mShader);
         }
         mRectF = new RectF(0,0,width,height);
         mWidth = width;
         mHeight = height;
      }

      int layerId = canvas.saveLayer(mRectF, null, Canvas.ALL_SAVE_FLAG);
      canvas.drawPath(mOuterPath,mPaint);
      mPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.CLEAR));
      canvas.drawPath(mInnerPath,mPaint);
      mPaint.setXfermode(null);
      canvas.restoreToCount(layerId);
   }

   @Override
   public void setAlpha(int alpha) {

   }

   @Override
   public void setColorFilter(@Nullable ColorFilter colorFilter) {

   }

   @Override
   public int getOpacity() {
      return PixelFormat.UNKNOWN;
   }
}

使用方法也很简单

         int[] colors = { Color.parseColor("#C084FF"), 	Color.parseColor("#8040FF") };
         //初始化并设置四个边框的宽度
         BorderDrawable borderDrawable = new BorderDrawable(5,5,5,30);
         //设置渐变色
         borderDrawable.setColors(colors);
         //设置圆角大小
         borderDrawable.setCornerRadius(20);
         //将设置好的，放到放到view里面即可
         view.setBackground(borderDrawable);

2.利用canvas裁剪实现，这个方法有个缺陷，就是圆角会出现毛边，也就是锯齿。

这个方法的思路基本上同上面一致，我们可以直接继承GradientDrawable来绘制外层的渐变背景，然后把颜色混合变成从原矩形中间进行画布的裁剪，把中间的画布给裁剪掉，这样不就只剩下边框了吗，哈哈哈。废话不多说，直接上代码啊。

/**
 * @des: 渐变背景边框
 * @author: 569133338@qq.com
 * @date: 2023/2/23 16:19
 */
public class BorderDrawable2 extends GradientDrawable {
   public int mLeftBorderWidth = 0;
   public int mRightBorderWidth = 0;
   public int mTopBorderWidth = 0;
   public int mBottomBorderWidth = 0;

   public float mBorderRadius =0;

   public float[] mBorderRadii;

   Path mPath = new Path();

   public BorderDrawable2(int borderWidth) {
      this(borderWidth,borderWidth,borderWidth,borderWidth);
   }

   @Override
   public void setCornerRadii(@Nullable float[] radii) {
      this.mBorderRadii = radii;
      super.setCornerRadii(radii);
   }

   @Override
   public void setCornerRadius(float radius) {
      this.mBorderRadius = radius;
      super.setCornerRadius(radius);
   }

   public BorderDrawable2(int leftBorderWidth, int rightBorderWidth, int topBorderWidth, int bottomBorderWidth) {
      mLeftBorderWidth = leftBorderWidth;
      mRightBorderWidth = rightBorderWidth;
      mTopBorderWidth = topBorderWidth;
      mBottomBorderWidth = bottomBorderWidth;
   }



   @Override
   public void draw(Canvas canvas) {
      int width = getBounds().width();
      int height = getBounds().height();
      if(Build.VERSION.SDK_INT >= 21){
         if(mBorderRadii != null){
            mPath.addRoundRect(mLeftBorderWidth,mTopBorderWidth,width-mRightBorderWidth,height-mBottomBorderWidth,mBorderRadii, Path.Direction.CW);
         }else {
            mPath.addRoundRect(mLeftBorderWidth,mTopBorderWidth,width-mRightBorderWidth,height-mBottomBorderWidth,mBorderRadius,mBorderRadius, Path.Direction.CW);
         }
      }else{
         if(mBorderRadii != null){
            mPath.addRoundRect(new RectF(mLeftBorderWidth,mTopBorderWidth,width-mRightBorderWidth,height-mBottomBorderWidth),mBorderRadii, Path.Direction.CW);
         }else {
            mPath.addRoundRect(new RectF(mLeftBorderWidth,mTopBorderWidth,width-mRightBorderWidth,height-mBottomBorderWidth),mBorderRadius,mBorderRadius, Path.Direction.CW);
         }
      }

      canvas.setDrawFilter(new PaintFlagsDrawFilter(0, Paint.FILTER_BITMAP_FLAG|Paint.ANTI_ALIAS_FLAG));
      canvas.clipPath(mPath, Region.Op.DIFFERENCE);
      super.draw(canvas);
   }
}

使用方法也一如既往的简单

         int[] colors = { Color.parseColor("#C084FF"), Color.parseColor("#8040FF") };
         //初始化并设置四个边框的宽度
         BorderDrawable2 borderDrawable2 = new BorderDrawable2(5,5,5,30);
         //设置渐变方向
         borderDrawable2.setOrientation(GradientDrawable.Orientation.LEFT_RIGHT);
         //设置渐变色
         borderDrawable2.setColors(colors);
         //设置圆角大小
         borderDrawable2.setCornerRadius(20);
         //将设置好的，放到放到view里面即可
         view.setBackground(borderDrawable2);

3.利用layer绘制边框

这种方法网上有一大堆教程，这里就不再赘述了，基本思路就是利用layer的两层item来实现，外层先绘制整体的背景色，内层比外层小一些像素，并盖在外层即可实现边框的效果。但这种实现方式有一种很大的缺陷，就是它不是真正意义上的边框，因为内层无法是透明的，如果是透明的，那么外层的颜色就露出来了，所以内层必须要用一个和整体控件一致的颜色来盖在上面，因此并不推荐这种方法。

好了，就写到这，祝大家天天开心。

服务器托管，北京服务器托管，服务器租用 http://www.hhisp.net