IOS Quartz2D 无法从当前上下文获取图像

Question

我错过了什么？卡了几个小时，drawRect 按预期绘制，getTheImage(( 从 viewcontoller UI 调用 UIGraphicsGetImageFromCurrentImageContext(( 返回 nil;尝试了许多变化。任何帮助，不胜感激。

- (id)initWithFrame:(CGRect)frame {
    self = [super initWithFrame:frame];
    if (self) {
    }
    return self;
}
- (void)drawRect:(CGRect)rect {
    CGContextRef context = UIGraphicsGetCurrentContext();
    UIGraphicsBeginImageContext(self.bounds.size);
    CGContextSetLineWidth(context, 5.0);
    CGContextSetStrokeColorWithColor(context, [[UIColor    blackColor]CGColor]);
    CGContextMoveToPoint(context,100.0,100.0);
    CGContextAddLineToPoint(context,200.0,200.0);
    CGContextMoveToPoint(context,200.0,200.0);
    CGContextAddLineToPoint(context,200.0,400.0);
    CGContextStrokePath(context);
}

-(UIImage *)getTheImage
{
    UIImage *drawImage = UIGraphicsGetImageFromCurrentImageContext();
    NSLog(@"drawImage %@",drawImage);
    return drawImage;
}

Answer 1

仅当基于位图的图形上下文是当前图形上下文时，才应调用此函数。如果当前上下文为 nil 或不是通过调用 UIGraphicsBeginImageContext 创建的，则此函数返回 nil。

看起来您的呼叫不在上下文中。

Answer 2

你能试试这个吗？

-(UIImage *)getTheImage
{
    UIGraphicsBeginImageContextWithOptions(self.bounds.size, NO, [UIScreen mainScreen].scale);
    [self drawViewHierarchyInRect:self.bounds afterScreenUpdates:YES];
    UIImage *drawImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    NSLog(@"drawImage %@",drawImage);
    return drawImage;
}