为什么CGContextSetFillColorWithColor和CGContextFillRects都抛出“invalid context 0x0”错误？

Question

此代码：

    let rect = CGRectMake( 0.0, 0.0, 16.0, 16.0 )
    let context = UIGraphicsGetCurrentContext()

    UIGraphicsBeginImageContext( rect.size )
    CGContextSetFillColorWithColor( context, color.CGColor )
    CGContextFillRect( context, rect )

    let image = UIGraphicsGetImageFromCurrentImageContext()

    UIGraphicsEndImageContext()

抛出这些错误：

MakeImage[60890] <Error>: CGContextSetFillColorWithColor: invalid context 0x0. If you want to see the backtrace, please set CG_CONTEXT_SHOW_BACKTRACE environmental variable.
MakeImage[60890] <Error>: CGContextFillRects: invalid context 0x0. If you want to see the backtrace, please set CG_CONTEXT_SHOW_BACKTRACE environmental variable.

CGRect大小似乎很好，other posts表示问题。那么还有什么不正确的设置呢？谢谢。

Answer 1

您需要在开始图像上下文后获取当前上下文。

（显然，当您调用此代码时，在致电UIGraphicsBeginImageContext()之前，没有当前上下文。因此UIGraphicsGetCurrentContext()会返回nil。）

let rect = CGRectMake( 0.0, 0.0, 16.0, 16.0 )
UIGraphicsBeginImageContext( rect.size )

let context = UIGraphicsGetCurrentContext()

CGContextSetFillColorWithColor( context, color.CGColor )
CGContextFillRect( context, rect )

let image = UIGraphicsGetImageFromCurrentImageContext()

UIGraphicsEndImageContext()

Answer 2

我的不好，这两个只是错误的方式：

UIGraphicsBeginImageContext( rect.size )
let context = UIGraphicsGetCurrentContext()