UITableViewCell 的子视图没有出现

Question

我有可以展开以显示一些子细节的表格单元格，我希望出现一个向下的三角形，让用户知道这是可能的。

这是创建三角形视图的代码...

-(UIView *)triangularViewWithWidth:(CGFloat)width height:(CGFloat)height pointsUp:(BOOL)pointsUp {
UIBezierPath *trianglePath = [UIBezierPath bezierPath];
if(pointsUp){
    [trianglePath moveToPoint:CGPointMake(width / 2, 0)];
    [trianglePath moveToPoint:CGPointMake(width, height)];
    [trianglePath moveToPoint:CGPointMake(0, height)];
    [trianglePath closePath];
} else {
    [trianglePath moveToPoint:CGPointMake(0, 0)];
    [trianglePath moveToPoint:CGPointMake(width, 0)];
    [trianglePath moveToPoint:CGPointMake(width / 2, height)];
    [trianglePath closePath];
}
CAShapeLayer *l = [CAShapeLayer layer];
l.path = trianglePath.CGPath;

UIView *triangleView = [[UIView alloc] initWithFrame:CGRectMake(0, 0, width, height)];
triangleView.layer.mask = l;
return triangleView;
}

以及实现它的代码...

-(void)drawTriangle {
if([self.detail.subDetails count]){
    self.openCloseTriangle = [self triangularViewWithWidth:100 height:100 pointsUp:NO];
    NSLog(@"triangle origin is: %@", NSStringFromCGPoint(self.openCloseTriangle.frame.origin));
    NSLog(@"triangle size is: %@", NSStringFromCGSize(self.openCloseTriangle.frame.size));
    self.openCloseTriangle.backgroundColor = [UIColor redColor];
    [self.contentView addSubview:self.openCloseTriangle];
    [self.contentView bringSubviewToFront:self.openCloseTriangle];
}
}

如果我注释掉这一行，代码会按预期工作（创建一个大的红色矩形）：

l.path = trianglePath.CGPath;

所以我想我对形状层有些不理解，但我在我的应用程序的另一部分使用基本相同的绘图代码，它工作正常。

point 和 rect NSLog 输出也检查得很好（即使它没有出现）：

三角形原点是：{0, 0} 三角形大小为：{100, 100}

Answer 1

您必须使用addLineToPoint: 而不是moveToPoint: 来创建路径：

-(UIView *)triangularViewWithWidth:(CGFloat)width height:(CGFloat)height pointsUp:(BOOL)pointsUp {
    UIBezierPath *trianglePath = [UIBezierPath bezierPath];
    if(pointsUp){
        [trianglePath moveToPoint:CGPointMake(width / 2, 0)];
        [trianglePath addLineToPoint:CGPointMake(width, height)];
        [trianglePath addLineToPoint:CGPointMake(0, height)];
        [trianglePath closePath];
    } else {
        [trianglePath moveToPoint:CGPointMake(0, 0)];
        [trianglePath addLineToPoint:CGPointMake(width, 0)];
        [trianglePath addLineToPoint:CGPointMake(width / 2, height)];
        [trianglePath closePath];
    }
    CAShapeLayer *l = [CAShapeLayer layer];
    l.path = trianglePath.CGPath;

    UIView *triangleView = [[UIView alloc] initWithFrame:CGRectMake(0, 0, width, height)];
    triangleView.layer.mask = l;    
    return triangleView;
}

---

还有这一行

self.openCloseTriangle = [self triangularViewWithWidth:100 height:100 pointsUp:NO];

是有问题的：视图属性通常应该是弱的，因为视图由视图层次结构拥有，但是如果您将新创建的视图直接分配给这样的属性，它可能会立即被释放。创建一个本地视图，将其添加到另一个视图，而不是将其分配给弱属性。

---

我的测试代码

#import "ViewController.h"

@interface ViewController ()
@property (weak) UIView *openCloseTriangle;
@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    [self drawTriangle];
}

-(UIView *)triangularViewWithWidth:(CGFloat)width height:(CGFloat)height pointsUp:(BOOL)pointsUp {
    UIBezierPath *trianglePath = [UIBezierPath bezierPath];
    if(pointsUp){
        [trianglePath moveToPoint:CGPointMake(width / 2, 0)];
        [trianglePath addLineToPoint:CGPointMake(width, height)];
        [trianglePath addLineToPoint:CGPointMake(0, height)];
        [trianglePath closePath];
    } else {
        [trianglePath moveToPoint:CGPointMake(0, 0)];
        [trianglePath addLineToPoint:CGPointMake(width, 0)];
        [trianglePath addLineToPoint:CGPointMake(width / 2, height)];
        [trianglePath closePath];
    }
    CAShapeLayer *l = [CAShapeLayer layer];
    l.path = trianglePath.CGPath;

    UIView *triangleView = [[UIView alloc] initWithFrame:CGRectMake(0, 0, width, height)];
    triangleView.layer.mask = l;    
    return triangleView;
}


-(void)drawTriangle {
    UIView * v= [self triangularViewWithWidth:100 height:100 pointsUp:NO];
    self.openCloseTriangle = v;
    NSLog(@"triangle origin is: %@", NSStringFromCGPoint(self.openCloseTriangle.frame.origin));
    NSLog(@"triangle size is: %@", NSStringFromCGSize(self.openCloseTriangle.frame.size));
    self.openCloseTriangle.backgroundColor = [UIColor redColor];
    [self.view addSubview:self.openCloseTriangle];
}

@end