iOS進入后台模糊界面

• 兩種方式，一種是截取當前界面，做高斯模糊
• 一種是直接搞一個模糊界面蓋在window最上層，推薦這種，方便性能好

1、截取當前界面模糊

• 這種方法比較耗性能，畢竟要截圖，查找window，再模糊處理。

- (void)screenShot {
    //  保證每次截取的都是最新的界面
    if(self.screenShotImageV) {
		[self.screenShotImageV removeFromSuperview];
	}
	CGSize imageSize = CGSizeZero;
	//屏幕朝向
	UIInterfaceOrientation orientation = [UIApplication sharedApplication].statusBarOrientation;
	if (UIInterfaceOrientationIsPortrait(orientation))
		imageSize = [UIScreen mainScreen].bounds.size;
	else
		imageSize = CGSizeMake([UIScreen mainScreen].bounds.size.height, [UIScreen mainScreen].bounds.size.width);

	UIGraphicsBeginImageContextWithOptions(imageSize, NO, 0);
	CGContextRef context = UIGraphicsGetCurrentContext();
	//按理應取用戶看見的那個window

	for (UIWindow *window in [[UIApplication sharedApplication] windows])
	{
		CGContextSaveGState(context);
		CGContextTranslateCTM(context, window.center.x, window.center.y);
		CGContextConcatCTM(context, window.transform);
		CGContextTranslateCTM(context, -window.bounds.size.width * window.layer.anchorPoint.x, -window.bounds.size.height * window.layer.anchorPoint.y);
		if (orientation == UIInterfaceOrientationLandscapeLeft)
		{
			CGContextRotateCTM(context, M_PI_2);
			CGContextTranslateCTM(context, 0, -imageSize.width);
		}
		else if (orientation == UIInterfaceOrientationLandscapeRight)
		{
			CGContextRotateCTM(context, -M_PI_2);
			CGContextTranslateCTM(context, -imageSize.height, 0);
		} else if (orientation == UIInterfaceOrientationPortraitUpsideDown) {
			CGContextRotateCTM(context, M_PI);
			CGContextTranslateCTM(context, -imageSize.width, -imageSize.height);
		}

		if ([window respondsToSelector:@selector(drawViewHierarchyInRect:afterScreenUpdates:)])
		{
			[window drawViewHierarchyInRect:window.bounds afterScreenUpdates:YES];
		}
		else
		{
			[window.layer renderInContext:context];
		}
		CGContextRestoreGState(context);
	}
	//截屏圖片
	UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
	//截屏圖片t處理后
	UIImage *gaussianImage = [self coreGaussianBlurImage:image blurNumber:30];
	//生成控件
	UIImageView *bgImgv = [[UIImageView alloc] initWithImage:gaussianImage];
	bgImgv.frame = CGRectMake(0, 0, imageSize.width, imageSize.height);
	self.screenShotImageV = bgImgv;
}

/**
   高斯模糊 處理

   @param image 要處理的image
   @param blur 模糊度
   @return 處理后的image
 */
- (UIImage *)coreGaussianBlurImage:(UIImage * _Nonnull)image blurNumber:(CGFloat)blur {

	if (!image) {
		return nil;
	}
	CIContext *context = [CIContext contextWithOptions:nil];
	CIImage *inputImage = [CIImage imageWithCGImage:image.CGImage];

	CIFilter *filter = [CIFilter filterWithName:@"CIGaussianBlur"];
	[filter setValue:inputImage forKey:kCIInputImageKey];
	[filter setValue:[NSNumber numberWithFloat:blur] forKey:@"inputRadius"];
	CIImage *result = [filter valueForKey:kCIOutputImageKey];
	CGImageRef cgImage = [context createCGImage:result fromRect:[inputImage extent]];

	UIImage *blurImage = [UIImage imageWithCGImage:cgImage];

	CGImageRelease(cgImage);

	return blurImage;

}

//顯示window
- (void)show {
    [self screenShot];
    [[UIApplication sharedApplication].delegate.window addSubview:self.screenShotImageV];
    [[UIApplication sharedApplication].delegate.window bringSubviewToFront:self.screenShotImageV];
}
//隱藏window
- (void)hidden {
	if(self.screenShotImageV) {
		[self.screenShotImageV removeFromSuperview];
	}
}

2、通用界面模糊

• 這種比較方便，只需要創建一個界面即可，和具體界面無關。

/**
 打開后台快照遮罩
 */
- (void)executePresentBlurSnapshot
{
    if (!self.effectView) {
        UIBlurEffect *effect = [UIBlurEffect effectWithStyle:UIBlurEffectStyleLight];
        UIVisualEffectView *effectView = [[UIVisualEffectView alloc] initWithEffect:effect];
        effectView.frame = CGRectMake(0, 0, SCREEN_WIDTH, SCREEN_HEIGHT);
        self.effectView = effectView;
    }
    [[UIApplication sharedApplication].delegate.window addSubview:self.effectView];
    [[UIApplication sharedApplication].delegate.window bringSubviewToFront:self.effectView];
}

/**
 關閉后台快照遮罩
 */
- (void)executeDismissBlurSnapshot
{
    if (self.effectView) {
        [self.effectView removeFromSuperview];
    }
}

• 在delegate控制顯示和隱藏

- (void)applicationWillResignActive:(UIApplication *)application {
    [[LQAboveBackgroundView sharedInstance] show];
}

- (void)applicationWillEnterForeground:(UIApplication *)application {
    [[LQAboveBackgroundView sharedInstance] hidden];  
}

- (void)applicationDidBecomeActive:(UIApplication *)application {
    [[LQAboveBackgroundView sharedInstance] hidden];
}