ios - 快速截图renderInContext : drawViewHierarchyInRect:afterScreenUpdates:

Question

 (UIImage *)screenshot_1
{

    UIGraphicsBeginImageContextWithOptions(self.view.bounds.size, NO, 0);   
    [self.view.layer renderInContext:UIGraphicsGetCurrentContext()];   
    UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    return image;   
}

---

(UIImage *)screenshot_2
{

    UIGraphicsBeginImageContextWithOptions(self.view.bounds.size, NO, 0);    
    [self.view drawViewHierarchyInRect:self.view.bounds afterScreenUpdates:YES];    
    UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    return image;  
}

然后在 ios 7.0 中:

CFAbsoluteTime start = CFAbsoluteTimeGetCurrent();
UIImage *image = [self screenshot_1];
CFAbsoluteTime end = CFAbsoluteTimeGetCurrent();
NSLog(@"cost : %f ms", (end - start) * 1000);

然后打印:成本:10.128021 ms

CFAbsoluteTime start = CFAbsoluteTimeGetCurrent();   
UIImage *image = [self screenshot_2];  
CFAbsoluteTime end = CFAbsoluteTimeGetCurrent();  
NSLog(@"cost : %f ms", (end - start) * 1000);  

然后打印:cost:68.924010 ms

我的问题是哪个快？

Answer 1

因为 10ms < 68ms 第一个显然更快 但是请注意，第一种方法不会应用您的 View 可能具有的某些转换，而第二种方法会。 如果您计划大量使用这些功能，您应该找到一种方法来重用共享的支持上下文。