在 objective-c 中的 2 点之间画线

Question

我想在两点之间画线。但是 UIGraphicsGetCurrentContext() 是 return null

ViewController.m

self.drawLine.firstPoint = self.btnPointOne.bounds.origin;
self.drawLine.secondPoint = self.btnPointTwo.bounds.origin;
[self.drawLine drawRect:self.drawWatchModeView.bounds];

DrawLine.h

@interface DrawLine : UIView{
    CGContextRef context;
}

@property (assign, nonatomic) CGPoint firstPoint;
@property (assign, nonatomic) CGPoint secondPoint;

DrawLine.m

- (id)initWithFrame:(CGRect)frame {
    if (self = [super initWithFrame:frame]) {
    }
    return self;
}

- (void)drawRect:(CGRect)rect {
    context = UIGraphicsGetCurrentContext();
    // Drawing code
    CGContextSetStrokeColorWithColor(context, [UIColor blackColor].CGColor);
    //line width
    CGContextSetLineWidth(context, 1.0);
    CGContextMoveToPoint(context, self.firstPoint.x, self.firstPoint.y);
    CGContextAddLineToPoint(context, self.secondPoint.x, self.secondPoint.y);
    // and now draw the Path!
    CGContextStrokePath(context);
}

但是报错

CGContextSetStrokeColorWithColor: invalid context 0x0. If you want to see the backtrace, please set CG_CONTEXT_SHOW_BACKTRACE environmental variable.
CGContextSetLineWidth: invalid context 0x0. If you want to see the backtrace, please set CG_CONTEXT_SHOW_BACKTRACE environmental variable.
CGContextMoveToPoint: invalid context 0x0. If you want to see the backtrace, please set CG_CONTEXT_SHOW_BACKTRACE environmental variable.
CGContextAddLineToPoint: invalid context 0x0. If you want to see the backtrace, please set CG_CONTEXT_SHOW_BACKTRACE environmental variable.
CGContextDrawPath: invalid context 0x0. If you want to see the backtrace, please set CG_CONTEXT_SHOW_BACKTRACE environmental variable.
CGContextSetStrokeColorWithColor: invalid context 0x0. If you want to see the backtrace, please set CG_CONTEXT_SHOW_BACKTRACE environmental variable.
CGContextSetLineWidth: invalid context 0x0. If you want to see the backtrace, please set CG_CONTEXT_SHOW_BACKTRACE environmental variable.
CGContextMoveToPoint: invalid context 0x0. If you want to see the backtrace, please set CG_CONTEXT_SHOW_BACKTRACE environmental variable.
CGContextAddLineToPoint: invalid context 0x0. If you want to see the backtrace, please set CG_CONTEXT_SHOW_BACKTRACE environmental variable.
CGContextDrawPath: invalid context 0x0. If you want to see the backtrace, please set CG_CONTEXT_SHOW_BACKTRACE environmental variable.
CGContextSetStrokeColorWithColor: invalid context 0x0. If you want to see the backtrace, please set CG_CONTEXT_SHOW_BACKTRACE environmental variable.
CGContextSetLineWidth: invalid context 0x0. If you want to see the backtrace, please set CG_CONTEXT_SHOW_BACKTRACE environmental variable.
CGContextMoveToPoint: invalid context 0x0. If you want to see the backtrace, please set CG_CONTEXT_SHOW_BACKTRACE environmental variable.
CGContextAddLineToPoint: invalid context 0x0. If you want to see the backtrace, please set CG_CONTEXT_SHOW_BACKTRACE environmental variable.
CGContextDrawPath: invalid context 0x0. If you want to see the backtrace, please set CG_CONTEXT_SHOW_BACKTRACE environmental variable.
CGContextSetStrokeColorWithColor: invalid context 0x0. If you want to see the backtrace, please set CG_CONTEXT_SHOW_BACKTRACE environmental variable.
CGContextSetLineWidth: invalid context 0x0. If you want to see the backtrace, please set CG_CONTEXT_SHOW_BACKTRACE environmental variable.
CGContextMoveToPoint: invalid context 0x0. If you want to see the backtrace, please set CG_CONTEXT_SHOW_BACKTRACE environmental variable.
CGContextAddLineToPoint: invalid context 0x0. If you want to see the backtrace, please set CG_CONTEXT_SHOW_BACKTRACE environmental variable.
CGContextDrawPath: invalid context 0x0. If you want to see the backtrace, please set CG_CONTEXT_SHOW_BACKTRACE environmental variable.

我尝试 UIViewControllerBasedStatusBarAppearance 设置 YES 它对我不起作用我尝试删除 UIViewControllerBasedStatusBarAppearance 它对我不起作用

Answer 1

你不能随便打电话给drawRect:，所以你的线路：

[self.drawLine drawRect:self.drawWatchModeView.bounds];

需要改问OS到运行一个抽奖周期。当发生这种情况时，绘图上下文将被设置并且一切都准备就绪。当你运行它明确表示上下文不存在。因此，将该行更改为：

[self.drawLine setNeedsDisplay];

或

[self.drawLine setNeedsDisplayInRect:self.drawWatchModeView.bounds];

在 objective-c 中的 2 点之间画线

draw line between 2 points in objective-c

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