折线图中如何填充渐变颜色

此方法实在矩形中填充渐变颜色，再将不需要保留的渐变色用背景颜色覆盖。作为记录留存。

#import "DrawCell.h"

#define VIEW_WIDTH self.frame.size.width

#define VIEW_HEIGHT self.frame.size.height

#define CELL_WIDTH (self.frame.size.width-60)/11.0

#define UIColorFromHex(s) [UIColor colorWithRed:(((s & 0xFF0000) >> 16))/255.0 green:(((s &0xFF00) >>8))/255.0 blue:((s &0xFF))/255.0 alpha:1.0]

@implementation DrawCell

-(instancetype)initWithFrame:(CGRect)frame

{

    self = [super initWithFrame:frame];

    if (self) {

        ;

    }

    return self;

}

-(void)addBottomLine{

    CGContextRef context = UIGraphicsGetCurrentContext();

    CGContextSetLineWidth(context, 1);

    UIColor *lineColor = UIColorFromHex(0xa0a0a0);

    CGContextSetStrokeColorWithColor(context, lineColor.CGColor);

    CGContextMoveToPoint(context, 0, VIEW_HEIGHT-20);

    CGContextAddLineToPoint(context, VIEW_WIDTH, VIEW_HEIGHT-20);

    CGContextStrokePath(context);

}

-(void)addBottomCoordinate{

    UIColor *lineColor = UIColorFromHex(0xa0a0a0);

    for (NSInteger i = 0; i < 12; i++) {

        CGFloat height = 6;

        if (i==0||i==11) {

            height = VIEW_HEIGHT-20;

        }

        CGContextRef context = UIGraphicsGetCurrentContext();

        CGContextSetLineWidth(context, 0.5);

        CGContextSetStrokeColorWithColor(context, lineColor.CGColor);

        CGContextMoveToPoint(context, 30+i*CELL_WIDTH, VIEW_HEIGHT-20);

        CGContextAddLineToPoint(context, 30+i*CELL_WIDTH, VIEW_HEIGHT-20-height);

        CGContextStrokePath(context);

    }

}

-(void)addBottomCoordinateTextLabel{

    

    for (NSInteger i=0; i<12; i++) {

        

        UILabel *label = [[UILabel alloc] init];

        label.textAlignment = NSTextAlignmentCenter;

        label.frame = CGRectMake(30+i*CELL_WIDTH-CELL_WIDTH/2, VIEW_HEIGHT-19, CELL_WIDTH, 19);

        [self addSubview:label];

        label.adjustsFontSizeToFitWidth = YES;

        label.minimumScaleFactor = 0.1;

        switch (i) {

            case 0:

            {

                label.text = @"Jan";

            }

                break;

            case 1:

            {

                label.text = @"Jan";

            }

                break;

            case 2:

            {

                label.text = @"Jan";

            }

                break;

            case 3:

            {

                label.text = @"Jan";

            }

                break;

            case 4:

            {

                label.text = @"Jan";

            }

                break;

            case 5:

            {

                label.text = @"Jan";

            }

                break;

            case 6:

            {

                label.text = @"Jan";

            }

                break;

            case 7:

            {

                label.text = @"Jan";

            }

                break;

            case 8:

            {

                label.text = @"Jan";

            }

                break;

            case 9:

            {

                label.text = @"Jan";

            }

                break;

            case 10:

            {

                label.text = @"Jan";

            }

                break;

            case 11:

            {

                label.text = @"Jan";

            }

                break;

            default:

                break;

        }

    }

}

-(NSMutableArray*)dataArray{

    if (_dataArray==nil) {

        _dataArray = [[NSMutableArray alloc] init];

        

        for (NSInteger i=0 ;i<13 ;i++) {

            

            CGFloat number = (float)(1+arc4random()%99)/100;

            NSLog(@"number is %f",number);

            [_dataArray addObject:[NSNumber numberWithFloat:number]];

        }

    }

    return _dataArray;

}

-(void)addDataArrayLine{

    

    CGContextRef context = UIGraphicsGetCurrentContext();

//方法1

//    CGFloat locations[2] = {0.0, 1.0};

//    CGFloat components[8] = {104.0/255.0, 225.0/255.0, 250.0/255.0, 1.0, 115.0/255.0, 134.0/255.0, 197.0/255.0, 1.0}; // yellow->red

//    

//    CGColorSpaceRef colorspace = CGColorSpaceCreateDeviceRGB();

//    CGGradientRef gradient = CGGradientCreateWithColorComponents(colorspace, components, locations, 2);

//    

//    CGPoint startPoint = CGPointMake(VIEW_WIDTH/2, 0);

//    CGPoint endPoint = CGPointMake(VIEW_WIDTH/2, VIEW_HEIGHT-20);

//    CGContextDrawLinearGradient(context, gradient, startPoint, endPoint, 0);

//    

//    CGGradientRelease(gradient);

//    CGColorSpaceRelease(colorspace);

//    CGContextSaveGState(context);

 

//方法2

    //    UIGraphicsPushContext(context);

    

    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();

    CGFloat locations[] = {0, 1};

//    UIColor *color1 = UIColorFromHex(0x7386c5);

//    UIColor *color0 = UIColorFromHex(0x68e1fa);

    UIColor *color0 = [UIColor colorWithRed:104.0/255.0 green:225.0/255.0 blue:250.0/255.0 alpha:0.75];

    UIColor *color1 = [UIColor colorWithRed:115.0/255.0 green:134.0/255.0 blue:197.0/255.0 alpha:0.75];

    NSArray *colors = @[(__bridge id)color0.CGColor, (__bridge id)color1.CGColor];

    CGGradientRef gradient = CGGradientCreateWithColors(colorSpace, (CFArrayRef) colors, locations);

    CGColorSpaceRelease(colorSpace);

    

    CGPoint startPoint = CGPointMake(VIEW_WIDTH/2, 0);

    CGPoint endPoint = CGPointMake(VIEW_WIDTH/2, VIEW_HEIGHT-20);

    CGContextDrawLinearGradient(context, gradient, startPoint, endPoint, 0);

    CGGradientRelease(gradient);

    

//    UIGraphicsPopContext();

    

//方法3

//    CIFilter *ciFilter = [CIFilter filterWithName:@"CILinearGradient"];

//    CGRect rect = CGRectMake(0, 0, VIEW_WIDTH, VIEW_HEIGHT-20);

//    UIColor *color0 = UIColorFromHex(0x7386c5);

//    UIColor *color1 = UIColorFromHex(0x68e1fa);

//    CGPoint startPoint = CGPointMake(0.5, 0);

//    CGPoint endPoint = CGPointMake(0.5, 1);

//    CIVector *vector0 = [CIVector vectorWithX:rect.size.width * startPoint.x Y:rect.size.height * (1 - startPoint.y)];

//    CIVector *vector1 = [CIVector vectorWithX:rect.size.width * endPoint.x Y:rect.size.height * (1 - endPoint.y)];

//    [ciFilter setValue:vector0 forKey:@"inputPoint0"];

//    [ciFilter setValue:vector1 forKey:@"inputPoint1"];

//    [ciFilter setValue:[CIColor colorWithCGColor:color1.CGColor] forKey:@"inputColor0"];

//    [ciFilter setValue:[CIColor colorWithCGColor:color0.CGColor] forKey:@"inputColor1"];

//    

//    CIImage *ciImage = ciFilter.outputImage;

//    

//    CIContext* con = [CIContext contextWithOptions:nil];

//    CGImageRef resultCGImage = [con createCGImage:ciImage

//                                         fromRect:rect];

//    UIImage *resultUIImage = [UIImage imageWithCGImage:resultCGImage];

//    CGImageRelease(resultCGImage);

//    [resultUIImage drawInRect:rect];

    

    

    //绘制折线图，并且其余不需要显示的部分，用白色覆盖。

    CGContextSetLineWidth(context, 1);

//    UIColor *lineColor = UIColorFromHex(0x68e1fa);

    CGContextSetStrokeColorWithColor(context, [UIColor whiteColor].CGColor);

    CGContextSetRGBFillColor (context, 1.0, 1.0, 1.0, 1.0);

    CGFloat fload = [[self.dataArray firstObject] floatValue];

    CGContextMoveToPoint(context, 0, (VIEW_HEIGHT-20)*(1.0-fload));

    for (NSInteger i =1; i<self.dataArray.count; i++) {

        CGFloat height = [[self.dataArray objectAtIndex:i] floatValue];

        CGContextAddLineToPoint(context,30+CELL_WIDTH*(i-1), (VIEW_HEIGHT-20)*(1.0-height));

    }

    

    CGContextAddLineToPoint(context,30+CELL_WIDTH*(self.dataArray.count-2), VIEW_HEIGHT-20);

    CGContextAddLineToPoint(context,VIEW_WIDTH, VIEW_HEIGHT-20);

    CGContextAddLineToPoint(context,VIEW_WIDTH, 0);

    CGContextAddLineToPoint(context,0, 0);

    CGContextAddLineToPoint(context,0, (VIEW_HEIGHT-20)*(1.0-fload));

    

    CGContextClosePath(context);

    CGContextDrawPath(context, kCGPathFillStroke);

    CGContextStrokePath(context);

    

//    CGContextRestoreGState(context);

    

}

-(void)addUnitTextPart{

    CGContextRef context = UIGraphicsGetCurrentContext();

    CGContextSetRGBFillColor (context,  1, 0, 0, 1.0);//设置填充颜色

    UIFont  *font = [UIFont boldSystemFontOfSize:15.0];//设置

    [@"kWh" drawInRect:CGRectMake(0, 0, 40, 20) withAttributes:@{NSFontAttributeName:font}];

    [@"kWh" drawInRect:CGRectMake(VIEW_WIDTH-40, 0, 40, 20) withAttributes:@{NSFontAttributeName:font}];

}

// Only override drawRect: if you perform custom drawing.

// An empty implementation adversely affects performance during animation.

- (void)drawRect:(CGRect)rect {

    // Drawing code

    NSLog(@"draw view");

    //底部label的添加

    [self addBottomCoordinateTextLabel];

    //顶部画图

    [self addDataArrayLine];

    

    //底部灰色的线

    [self addBottomLine];

    

    //底部坐标的绘制

    [self addBottomCoordinate];

    

    //添加kwh的文字处理

    [self addUnitTextPart];

    

}

-(void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event{

}

-(void)touchesEnded:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event{

}

-(void)touchesMoved:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event{

}