在表格视图单元格背景上放置渐变

Question

我一直在尝试通过多种方式为我的表格视图单元格背景添加渐变，但似乎都没有效果。我一直在尝试用石英核心图形的东西来绘制它，将背景插座放在 IB 上的不同视图中，将 imageview 放在后面，并带有代码。似乎没有人以某种方式出现在背面，我不明白出了什么问题。需要的我可以详细说明，谢谢！

Answer 1

我在this question 中找到了一些代码，并对其进行了修改以适用于我的应用程序。它适用于普通表和分组表。

//
//  UAGradientCellBackgroundLayer.h
//

#import <Foundation/Foundation.h>
#import <UIKit/UIKit.h>

#import <QuartzCore/QuartzCore.h>

@class UAGradientCellBackgroundView;

@interface UAGradientCellBackgroundLayer : CAGradientLayer {
    CGFloat     *colorComponents;
    BOOL        _override;
}

@property(nonatomic,assign) BOOL override;

- (void)setColorComponents:(CGFloat *)components;

@end

//
//  UAGradientCellBackgroundLayer.m
//

#import "UAGradientCellBackgroundLayer.h"
#import "UAGradientCellBackgroundView.h"

#define TABLE_CELL_BACKGROUND                                   {1, 1, 1, 1, 204/255.0, 204/255.0, 204/255.0, 1}        // #FFFFFF and #DDDDDD

@implementation UAGradientCellBackgroundLayer

@synthesize override = _override;

///////////////////////////////////////////////////////////////////////////////////////////////////
- (id)init { 
    if ((self = [super init])) {
        colorComponents = NSZoneMalloc(NSDefaultMallocZone(), 8*sizeof(CGFloat));
        CGFloat c[8] = TABLE_CELL_BACKGROUND;
        for (int i = 0; i < 8; i++) {
            colorComponents[i] = c[i];
        }
        // self.cornerRadius = 10;
        // self.backgroundColor = [UIColor clearColor].CGColor;
    }
    return self;
}

- (void) dealloc {
    NSZoneFree(NSDefaultMallocZone(), colorComponents);
    [super dealloc];
}
- (void)display {
    if (_override) {
        self.colors =
        [NSArray arrayWithObjects:
         (id)[UIColor colorWithRed:colorComponents[0] green:colorComponents[1] blue:colorComponents[2] alpha:colorComponents[3]].CGColor,
         (id)[UIColor colorWithRed:colorComponents[4] green:colorComponents[5] blue:colorComponents[6] alpha:colorComponents[7]].CGColor,
         nil];
    } else {
        self.colors =
        [NSArray arrayWithObjects:
         (id)[UIColor clearColor].CGColor,
         (id)[UIColor clearColor].CGColor,
         nil];
    }
    [super display];
}

- (void)setColorComponents:(CGFloat *)components {
    for (int i = 0; i < 8; i++) {
        colorComponents[i] = components[i];
    }
}

@end 

//
//  UAGradientCellBackgroundView.h
//

#import <Foundation/Foundation.h>

#import <UIKit/UIKit.h>

typedef enum  {
    UAGradientCellBackgroundViewPositionMiddle = 0,
    UAGradientCellBackgroundViewPositionTop,
    UAGradientCellBackgroundViewPositionBottom,
    UAGradientCellBackgroundViewPositionSingle,
    UAGradientCellBackgroundViewPositionPlain
} UAGradientCellBackgroundViewPosition;

@interface UAGradientCellBackgroundView : UIView {
    UAGradientCellBackgroundViewPosition position;
    CGFloat colors[8];
}

@property(nonatomic, assign) UAGradientCellBackgroundViewPosition position;

- (void)setColors:(CGFloat[8])comps;

@end

//
//  UAGradientCellBackgroundView.m
//

#import "UAGradientCellBackgroundView.h"
#import "UAGradientCellBackgroundLayer.h"
#import <QuartzCore/QuartzCore.h>

#define kDefaultMargin                                          10
#define TABLE_CELL_BACKGROUND                                   {1, 1, 1, 1, 204/255.0, 204/255.0, 204/255.0, 1}        // #FFFFFF and #DDDDDD

static void addRoundedRectToPath(CGContextRef context, CGRect rect,
                                 float ovalWidth,float ovalHeight);

@implementation UAGradientCellBackgroundView

@synthesize position;

//////////////////////////////////////////////////////////////////////
// PLAIN CELL
//
// layerClass
//
// returns a CAGradientLayer class as the default layer class for this view
//
+ (Class)layerClass {
    return [UAGradientCellBackgroundLayer class];
}

//////////////////////////////////////////////////////////////////////
- (void)updateLayer {
    UAGradientCellBackgroundLayer* layer = (UAGradientCellBackgroundLayer*)self.layer;
        // This is dramatically faster than calling drawRect.
    [layer setColorComponents:colors];
    layer.override = (self.position == UAGradientCellBackgroundViewPositionPlain);
    [layer setNeedsDisplay];
}

////////////////////////////////////////////////////////////////////
// GROUPED CELL
- (void)setColors:(CGFloat[8])comps {
    for (int i = 0; i < 8; i++) {
        colors[i] = comps[i];
    }
}

- (BOOL)isOpaque {
    return YES;
}

- (id)initWithFrame:(CGRect)frame {
    self = [super initWithFrame:frame];
    if (self != nil) {
        CGFloat comps[8] = TABLE_CELL_BACKGROUND;
        [self setColors:comps];
    }
    return self;
}

- (void)debugView:(UIView *)view {
    NSLog(@"%@ - %@", view.backgroundColor, [[view class] description]);
    for (UIView* child in view.subviews) {
        [self debugView:child];
    }
}

-(void)drawRect:(CGRect)aRect {
    [super drawRect:aRect];
    // Drawing code
    if (position == UAGradientCellBackgroundViewPositionPlain) {
        return;
    }

    CGContextRef c = UIGraphicsGetCurrentContext(); 

    // TODO - Dirty, Dirty hack to fix the background black corners on pop issue. doesnt handle rotation.
//  CGContextSetFillColorWithColor(c, [UAColor offsetPinstripesColor].CGColor);
//  CGContextFillRect(c, aRect);

    int lineWidth = 1;

    CGRect rect = [self bounds];
    rect.size.width -= lineWidth;
    rect.size.height -= lineWidth;
    rect.origin.x += lineWidth / 2.0;
    rect.origin.y += lineWidth / 2.0;

    CGFloat minx = CGRectGetMinX(rect), midx = CGRectGetMidX(rect), maxx = CGRectGetMaxX(rect);
    CGFloat miny = CGRectGetMinY(rect), midy = CGRectGetMidY(rect), maxy = CGRectGetMaxY(rect);
    miny -= 1;

    CGFloat locations[2] = { 0.0, 1.0 };    
    CGColorSpaceRef myColorspace = CGColorSpaceCreateDeviceRGB();
    CGGradientRef myGradient = nil;

    CGContextSetStrokeColorWithColor(c, [UIColor darkGrayColor].CGColor);
    CGContextSetLineWidth(c, lineWidth);
    CGContextSetAllowsAntialiasing(c, YES);
    CGContextSetShouldAntialias(c, YES);

    if (position == UAGradientCellBackgroundViewPositionTop) {
        miny += 1;

        CGMutablePathRef path = CGPathCreateMutable();
        CGPathMoveToPoint(path, NULL, minx, maxy);
        CGPathAddArcToPoint(path, NULL, minx, miny, midx, miny, kDefaultMargin);
        CGPathAddArcToPoint(path, NULL, maxx, miny, maxx, maxy, kDefaultMargin);
        CGPathAddLineToPoint(path, NULL, maxx, maxy);
        CGPathAddLineToPoint(path, NULL, minx, maxy);
        CGPathCloseSubpath(path);

        // Fill and stroke the path
        CGContextSaveGState(c);
        CGContextAddPath(c, path);
        CGContextClip(c);

        myGradient = CGGradientCreateWithColorComponents(myColorspace, colors, locations, 2);
        CGContextDrawLinearGradient(c, myGradient, CGPointMake(minx,miny), CGPointMake(minx,maxy), 0);

        CGContextAddPath(c, path);
        CGPathRelease(path);
        CGContextStrokePath(c);
        CGContextRestoreGState(c);

    } else if (position == UAGradientCellBackgroundViewPositionBottom) {
        //maxy -= 1; // -1 for the shadow 

        CGMutablePathRef path = CGPathCreateMutable();
        CGPathMoveToPoint(path, NULL, minx, miny);
        CGPathAddArcToPoint(path, NULL, minx, maxy, midx, maxy, kDefaultMargin);
        CGPathAddArcToPoint(path, NULL, maxx, maxy, maxx, miny, kDefaultMargin);
        CGPathAddLineToPoint(path, NULL, maxx, miny);
        CGPathAddLineToPoint(path, NULL, minx, miny);
        CGPathCloseSubpath(path);

        // Fill and stroke the path
        CGContextSaveGState(c);
        CGContextAddPath(c, path);
        CGContextClip(c);

        myGradient = CGGradientCreateWithColorComponents(myColorspace, colors, locations, 2);
        CGContextDrawLinearGradient(c, myGradient, CGPointMake(minx,miny), CGPointMake(minx,maxy), 0);

        CGContextAddPath(c, path);
        CGPathRelease(path);
        CGContextStrokePath(c);
        CGContextRestoreGState(c);


    } else if (position == UAGradientCellBackgroundViewPositionMiddle) {

        CGMutablePathRef path = CGPathCreateMutable();
        CGPathMoveToPoint(path, NULL, minx, miny);
        CGPathAddLineToPoint(path, NULL, maxx, miny);
        CGPathAddLineToPoint(path, NULL, maxx, maxy);
        CGPathAddLineToPoint(path, NULL, minx, maxy);
        CGPathAddLineToPoint(path, NULL, minx, miny);
        CGPathCloseSubpath(path);

        // Fill and stroke the path
        CGContextSaveGState(c);
        CGContextAddPath(c, path);
        CGContextClip(c);

        myGradient = CGGradientCreateWithColorComponents(myColorspace, colors, locations, 2);
        CGContextDrawLinearGradient(c, myGradient, CGPointMake(minx,miny), CGPointMake(minx,maxy), 0);

        CGContextAddPath(c, path);
        CGPathRelease(path);
        CGContextStrokePath(c);
        CGContextRestoreGState(c);

    } else if (position == UAGradientCellBackgroundViewPositionSingle) {
        miny += 1;
        //maxy -= 1; // -1 for the shadow 

        CGMutablePathRef path = CGPathCreateMutable();
        CGPathMoveToPoint(path, NULL, minx, midy);
        CGPathAddArcToPoint(path, NULL, minx, miny, midx, miny, kDefaultMargin);
        CGPathAddArcToPoint(path, NULL, maxx, miny, maxx, midy, kDefaultMargin);
        CGPathAddArcToPoint(path, NULL, maxx, maxy, midx, maxy, kDefaultMargin);
        CGPathAddArcToPoint(path, NULL, minx, maxy, minx, midy, kDefaultMargin);
        CGPathCloseSubpath(path);

        // Shadow
//      CGContextAddPath(c, path);
//      CGContextSaveGState(c);
//      CGContextSetShadow(c, CGSizeMake(0, -1), 1);
//      CGContextFillPath(c);

        // Fill and stroke the path
        CGContextSaveGState(c);
        CGContextAddPath(c, path);
        CGContextClip(c);


        myGradient = CGGradientCreateWithColorComponents(myColorspace, colors, locations, 2);
        CGContextDrawLinearGradient(c, myGradient, CGPointMake(minx,miny), CGPointMake(minx,maxy), 0);

        CGContextAddPath(c, path);
        CGPathRelease(path);
        CGContextStrokePath(c);
        CGContextRestoreGState(c);

    }
    CGColorSpaceRelease(myColorspace);
    CGGradientRelease(myGradient);
    return;
}

- (void)setPosition:(UAGradientCellBackgroundViewPosition)newPosition {
    if (position != newPosition) {
        position = newPosition;
        [self updateLayer];
    }
}

@end

static void addRoundedRectToPath(CGContextRef context, CGRect rect, float ovalWidth,float ovalHeight) {
    float fw, fh;

    if (ovalWidth == 0 || ovalHeight == 0) {// 1
        CGContextAddRect(context, rect);
        return;
    }

    CGContextSaveGState(context);// 2

    CGContextTranslateCTM (context, CGRectGetMinX(rect),// 3
                           CGRectGetMinY(rect));
    CGContextScaleCTM (context, ovalWidth, ovalHeight);// 4
    fw = CGRectGetWidth (rect) / ovalWidth;// 5
    fh = CGRectGetHeight (rect) / ovalHeight;// 6

    CGContextMoveToPoint(context, fw, fh/2); // 7
    CGContextAddArcToPoint(context, fw, fh, fw/2, fh, 1);// 8
    CGContextAddArcToPoint(context, 0, fh, 0, fh/2, 1);// 9
    CGContextAddArcToPoint(context, 0, 0, fw/2, 0, 1);// 10
    CGContextAddArcToPoint(context, fw, 0, fw, fh/2, 1); // 11
    CGContextClosePath(context);// 12

    CGContextRestoreGState(context);// 13
} 

使用示例（普通表）：

#import "UAGradientCellBackgroundView.h" 
CGFloat COLORS[8] = { 0.0/255, 0.0/255, 255.0/255, 1.0, 0.0/255, 0.0/255, 0.0/255, 1.0 }
...

- (UITableViewCell *)tableView:(UITableView *)table cellForRowAtIndexPath:(NSIndexPath *)indexPath { 
    NSString *cellID = @"CellID";

    // create cell
    UITableViewCell *cell = (UITableViewCell *)[table dequeueReusableCellWithIdentifier:cellID];
    if (cell == nil) {
        cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:cellID] autorelease];

        UAGradientCellBackgroundView *bgView = [[[UAGradientCellBackgroundView alloc] initWithFrame:CGRectZero] autorelease];
        [bgView setBackgroundColor:[UIColor clearColor]];
        [bgView setColors:COLORS];
        [bgView setPosition:UAGradientCellBackgroundViewPositionPlain];
        cell.selectedBackgroundView = bgView;
        cell.textLabel.backgroundColor = [UIColor clearColor];

        cell.imageView.image = [UIImage imageNamed:@"cellimg.png"];
    }

    cell.textLabel.text = @"Text";
    return cell; 
}