总结iOS实现渐变颜色的三种方法

在ios开发过程中有的时候会需要用到渐变的颜色，这篇文章总结了三种方法来实现，有需要的朋友们下面来一起看看吧。

一、cagradientlayer实现渐变

cagradientlayer是calayer的一个特殊子类，用于生成颜色渐变的图层，使用较为方便

下面介绍下它的相关属性：

      colors 渐变的颜色

      locations 渐变颜色的分割点

      startpoint&endpoint 颜色渐变的方向，范围在(0,0)与(1.0,1.0)之间，如(0,0)(1.0,0)代表水平方向渐变,(0,0)(0,1.0)代表竖直方向渐变

 cagradientlayer *gradientlayer = [cagradientlayer layer];
 gradientlayer.colors = @[(__bridge id)[uicolor redcolor].cgcolor, (__bridge id)[uicolor yellowcolor].cgcolor, (__bridge id)[uicolor bluecolor].cgcolor];
 gradientlayer.locations = @[@0.3, @0.5, @1.0];
 gradientlayer.startpoint = cgpointmake(0, 0);
 gradientlayer.endpoint = cgpointmake(1.0, 0);
 gradientlayer.frame = cgrectmake(0, 100, 300, 100);
 [self.view.layer addsublayer:gradientlayer];

cagradientlayer实现渐变标间简单直观，但存在一定的局限性，比如无法自定义整个渐变区域的形状，如环形、曲线形的渐变。

二、core graphics相关方法实现渐变

ios core graphics中有两个方法用于绘制渐变颜色，cgcontextdrawlineargradient可以用于生成线性渐变，cgcontextdrawradialgradient用于生成圆半径方向颜色渐变。函数可以自定义path，无论是什么形状都可以，原理都是用来做clip，所以需要在cgcontextclip函数前调用cgcontextaddpath函数把cgpathref加入到context中。
另外一个需要注意的地方是渐变的方向，方向是由两个点控制的，点的单位就是坐标。因此需要正确从cgpathref中找到正确的点，方法当然有很多种看具体实现，本例中，我就是简单得通过调用cgpathgetboundingbox函数，返回cgpathref的矩形区域，然后根据这个矩形取两个点，读者可以根据自行需求修改具体代码。

1-> 线性渐变

- (void)drawlineargradient:(cgcontextref)context
  path:(cgpathref)path
 startcolor:(cgcolorref)startcolor
  endcolor:(cgcolorref)endcolor
{
 cgcolorspaceref colorspace = cgcolorspacecreatedevicergb();
 cgfloat locations[] = { 0.0, 1.0 };

 nsarray *colors = @[(__bridge id) startcolor, (__bridge id) endcolor];

 cggradientref gradient = cggradientcreatewithcolors(colorspace, (__bridge cfarrayref) colors, locations);


 cgrect pathrect = cgpathgetboundingbox(path);

 //具体方向可根据需求修改
 cgpoint startpoint = cgpointmake(cgrectgetminx(pathrect), cgrectgetmidy(pathrect));
 cgpoint endpoint = cgpointmake(cgrectgetmaxx(pathrect), cgrectgetmidy(pathrect));

 cgcontextsavegstate(context);
 cgcontextaddpath(context, path);
 cgcontextclip(context);
 cgcontextdrawlineargradient(context, gradient, startpoint, endpoint, 0);
 cgcontextrestoregstate(context);

 cggradientrelease(gradient);
 cgcolorspacerelease(colorspace);
}

- (void)viewdidload 
{
 [super viewdidload];
 // do any additional setup after loading the view.

 //创建cgcontextref
 uigraphicsbeginimagecontext(self.view.bounds.size);
 cgcontextref gc = uigraphicsgetcurrentcontext();

 //创建cgmutablepathref
 cgmutablepathref path = cgpathcreatemutable();

 //绘制path
 cgrect rect = cgrectmake(0, 100, 300, 200);
 cgpathmovetopoint(path, null, cgrectgetminx(rect), cgrectgetminy(rect));
 cgpathaddlinetopoint(path, null, cgrectgetmidx(rect), cgrectgetmaxy(rect));
 cgpathaddlinetopoint(path, null, cgrectgetwidth(rect), cgrectgetmaxy(rect));
 cgpathclosesubpath(path);

 //绘制渐变
 [self drawlineargradient:gc path:path startcolor:[uicolor greencolor].cgcolor endcolor:[uicolor redcolor].cgcolor];

 //注意释放cgmutablepathref
 cgpathrelease(path);

 //从context中获取图像，并显示在界面上
 uiimage *img = uigraphicsgetimagefromcurrentimagecontext();
 uigraphicsendimagecontext();

 uiimageview *imgview = [[uiimageview alloc] initwithimage:img];
 [self.view addsubview:imgview];
}

2-> 圆半径方向渐变

- (void)drawradialgradient:(cgcontextref)context
  path:(cgpathref)path
 startcolor:(cgcolorref)startcolor
  endcolor:(cgcolorref)endcolor
{
 cgcolorspaceref colorspace = cgcolorspacecreatedevicergb();
 cgfloat locations[] = { 0.0, 1.0 };

 nsarray *colors = @[(__bridge id) startcolor, (__bridge id) endcolor];

 cggradientref gradient = cggradientcreatewithcolors(colorspace, (__bridge cfarrayref) colors, locations);


 cgrect pathrect = cgpathgetboundingbox(path);
 cgpoint center = cgpointmake(cgrectgetmidx(pathrect), cgrectgetmidy(pathrect));
 cgfloat radius = max(pathrect.size.width / 2.0, pathrect.size.height / 2.0) * sqrt(2);

 cgcontextsavegstate(context);
 cgcontextaddpath(context, path);
 cgcontexteoclip(context);

 cgcontextdrawradialgradient(context, gradient, center, 0, center, radius, 0);

 cgcontextrestoregstate(context);

 cggradientrelease(gradient);
 cgcolorspacerelease(colorspace);
}

- (void)viewdidload 
{
 [super viewdidload];
 // do any additional setup after loading the view.

 //创建cgcontextref
 uigraphicsbeginimagecontext(self.view.bounds.size);
 cgcontextref gc = uigraphicsgetcurrentcontext();

 //创建cgmutablepathref
 cgmutablepathref path = cgpathcreatemutable();

 //绘制path
 cgrect rect = cgrectmake(0, 100, 300, 200);
 cgpathmovetopoint(path, null, cgrectgetminx(rect), cgrectgetminy(rect));
 cgpathaddlinetopoint(path, null, cgrectgetmidx(rect), cgrectgetmaxy(rect));
 cgpathaddlinetopoint(path, null, cgrectgetwidth(rect), cgrectgetmaxy(rect));
 cgpathaddlinetopoint(path, null, cgrectgetwidth(rect), cgrectgetminy(rect));
 cgpathclosesubpath(path);

 //绘制渐变
 [self drawradialgradient:gc path:path startcolor:[uicolor greencolor].cgcolor endcolor:[uicolor redcolor].cgcolor];

 //注意释放cgmutablepathref
 cgpathrelease(path);

 //从context中获取图像，并显示在界面上
 uiimage *img = uigraphicsgetimagefromcurrentimagecontext();
 uigraphicsendimagecontext();

 uiimageview *imgview = [[uiimageview alloc] initwithimage:img];
 [self.view addsubview:imgview];
}

三、以cashapelayer作为layer的mask属性

calayer的mask属性可以作为遮罩让layer显示mask遮住(非透明)的部分；cashapelayer为calayer的子类，通过path属性可以生成不同的形状，将cashapelayer对象用作layer的mask属性的话，就可以生成不同形状的图层。

故生成颜色渐变有以下几个步骤：

     1、生成一个imageview(也可以为layer)，image的属性为颜色渐变的图片

     2、生成一个cashapelayer对象，根据path属性指定所需的形状

     3、将cashapelayer对象赋值给imageview的mask属性

- (void)viewdidload
{
 [super viewdidload];

 [self.view addsubview:self.firstcircle];
 _firstcircle.frame = cgrectmake(0, 0, 200, 200);
 _firstcircle.center = cgpointmake(cgrectgetwidth(self.view.bounds) / 2.0, cgrectgetheight(self.view.bounds) / 2.0);
 cgfloat firscirclewidth = 5;
 self.firstcircleshapelayer = [self generateshapelayerwithlinewidth:firscirclewidth];
 _firstcircleshapelayer.path = [self generatebezierpathwithcenter:cgpointmake(100, 100) radius:100].cgpath;
 _firstcircle.layer.mask = _firstcircleshapelayer;
} 

- (cashapelayer *)generateshapelayerwithlinewidth:(cgfloat)linewidth
{
 cashapelayer *waveline = [cashapelayer layer];
 waveline.linecap = kcalinecapbutt;
 waveline.linejoin = kcalinejoinround;
 waveline.strokecolor = [uicolor redcolor].cgcolor;
 waveline.fillcolor = [[uicolor clearcolor] cgcolor];
 waveline.linewidth = linewidth;
 waveline.backgroundcolor = [uicolor clearcolor].cgcolor;

 return waveline;
}

- (uibezierpath *)generatebezierpathwithcenter:(cgpoint)center radius:(cgfloat)radius
{
 uibezierpath *circlepath = [uibezierpath bezierpathwitharccenter:center radius:radius startangle:0 endangle:2*m_pi clockwise:no];

 return circlepath;
}

- (uiimageview *)firstcircle
{
 if (!_firstcircle) {
 self.firstcircle = [[uiimageview alloc] initwithimage:[uiimage imagenamed:@"circlebackground"]];
 _firstcircle.layer.maskstobounds = yes;
 _firstcircle.alpha = 1.0;
 }

 return _firstcircle;
}

总结

以上就是这篇文章的全部内容了，希望本文的内容对各位ios开发者们能有所帮助，如果有疑问大家可以留言交流。