将 UIView 保存为透明 PNG

Question

我有一个 UIView，我希望它存储为透明 PNG，即没有 UIVIew 背景颜色...

我目前正在使用此代码，它工作正常，但具有背景颜色:(

UIGraphicsBeginImageContext(self.bounds.size);
[self.layer renderInContext:UIGraphicsGetCurrentContext()];
UIImage* image1 = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
NSData *imageData = UIImagePNGRepresentation(image1);
[imageData writeToFile:filePath atomically:YES];

那么有人知道如何获取这张图片是透明的吗？

提前谢谢你..

Answer 1

就我而言，我忘记了不透明的属性。应将其设置为“否”：

view.opaque = NO;

Answer 2

将背景颜色更改为[UIColorclear]，绘制图像然后将背景颜色设置回原始颜色。

由于 GUI 更新仅在下一个运行循环周期触发，因此用户不应看到任何闪烁。

UIColor* color=self.backgroundColor;
view.backgroundColor=[UIColor clearColor];

UIGraphicsBeginImageContext(self.bounds.size);
[self.layer renderInContext:UIGraphicsGetCurrentContext()];
UIImage* image1 = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
NSData *imageData = UIImagePNGRepresentation(image1);
[imageData writeToFile:filePath atomically:YES];

self.backgroundColor=color;

Answer 3

作为吉拉德答案的补充。在视网膜显示屏上，这可能会导致一些质量问题。要获取视网膜上下文，您可以使用这篇帖子中的代码。

UIColor* color=self.backgroundColor;
view.backgroundColor=[UIColor clearColor];

// This is for retina render check
UIWindow *keyWindow = [[UIApplication sharedApplication] keyWindow];
if ([[UIScreen mainScreen] respondsToSelector:@selector(scale)])
    UIGraphicsBeginImageContextWithOptions(YourView.frame.size, NO, [UIScreen mainScreen].scale);
else
    UIGraphicsBeginImageContext(keyWindow.bounds.size);
// And it goes up to here the rest stays the same

[self.layer renderInContext:UIGraphicsGetCurrentContext()];
UIImage* image1 = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
NSData *imageData = UIImagePNGRepresentation(image1);
[imageData writeToFile:filePath atomically:YES];

self.backgroundColor=color;

Answer 4

对于 Objective-c，你必须设置 opaque = NO

 + (UIImage *) imageWithView:(UIView *)view 
    {     
        UIGraphicsBeginImageContextWithOptions(view.bounds.size, NO, [[UIScreen mainScreen] scale]);     
        [view.layer renderInContext:UIGraphicsGetCurrentContext()];     
        UIImage * img = UIGraphicsGetImageFromCurrentImageContext();     
        UIGraphicsEndImageContext();     
        return img; 
    }

对于 Swift，你必须设置 opaque = false

func imageWithView(inView: UIView) -> UIImage? {
        UIGraphicsBeginImageContextWithOptions(inView.bounds.size, false, 0.0)
        if let context = UIGraphicsGetCurrentContext() {
            inView.layer.render(in: context)
            let image = UIGraphicsGetImageFromCurrentImageContext()
            UIGraphicsEndImageContext()
            return image
        }
        return nil
    }