问题
I wan't a imageview which is semi-transparent in other parts and completely transparent in the middle .. see this image..
i have managed to do it but it is not the best of ways.. can I only have a rect inside yellow lines transparent ...?
EDIT: Is it possible to change the alpha of a certain rect of a view..?
回答1:
Place a custom UIView over the view showing the image, size and position it to exactly overlap. In the custom view's drawRect method
- (void)drawRect:(CGRect)rect { // Drawing code CGRect rBounds = self.bounds; CGContextRef context = UIGraphicsGetCurrentContext(); // Fill background with 80% white CGContextSetFillColorWithColor(context, [[[UIColor whiteColor] colorWithAlphaComponent:0.8] CGColor]); CGContextFillRect(context, rBounds); // Draw the window 'frame' CGContextSetStrokeColorWithColor(context, [[UIColor orangeColor] CGColor]); CGContextSetLineWidth(context, 10); CGContextStrokeRect(context, self.maskRect); // make the window transparent CGContextSetBlendMode(context, kCGBlendModeClear); CGContextFillRect(context, self.maskRect); } where maskRect is the rectangle to be shown transparent. Do ensure that the background color of the custom view is set to 'clearColor'
You can write any additional logic required to change the maskRect and call 'setNeedsDisplay' on this view.
回答2:
After lots of effort, I have found the solution.
Here is the code for it!!
-(void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event { [screenShotButton setHidden:YES]; UITouch *touch = [touches anyObject]; CGPoint pnt =[touch locationInView:self.view]; CGRect viewFrame=changeView.frame; CGFloat x1Diff,y1Diff,x2Diff,y2Diff; x1Diff=ABS(viewFrame.origin.x-pnt.x); y1Diff=ABS(viewFrame.origin.y-pnt.y); x2Diff=ABS(viewFrame.origin.x+viewFrame.size.width-pnt.x); y2Diff=ABS(viewFrame.origin.y+viewFrame.size.height-pnt.y); if (x1Diff<=10) { left=YES; shouldExpand=YES; } if (y1Diff<10) { top=YES; shouldExpand=YES; } if (x2Diff<=10) { right=YES; shouldExpand=YES; } if (y2Diff<=10) { bottom=YES; shouldExpand=YES; } if(CGRectContainsPoint(changeView.frame, pnt)) { shouldChange=YES; fromPoint=pnt; } else { shouldChange=NO; } } -(void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event { if (!shouldChange) { return; } if (shouldExpand) { UITouch *touch = [touches anyObject]; CGPoint pnt =[touch locationInView:self.view]; CGRect preFram =changeView.frame; CGRect modifiedFrame=preFram; if (left) { modifiedFrame.origin.x=preFram.origin.x-(fromPoint.x-pnt.x); modifiedFrame.size.width=preFram.size.width+fromPoint.x-pnt.x; fromPoint.x=pnt.x; } if (right) { modifiedFrame.size.width=preFram.size.width+pnt.x-fromPoint.x; fromPoint.x=pnt.x; } if (top) { modifiedFrame.origin.y=preFram.origin.y-(fromPoint.y-pnt.y); modifiedFrame.size.height=preFram.size.height+fromPoint.y-pnt.y; fromPoint.y=pnt.y; } if (bottom) { modifiedFrame.size.height=preFram.size.height+pnt.y-fromPoint.y; fromPoint.y=pnt.y; } changeView.frame=modifiedFrame; [clearImage setBounds:CGRectMake(0-modifiedFrame.origin.x, 0-modifiedFrame.origin.y, clearImage.frame.size.width, clearImage.frame.size.height)]; } else { UITouch *touch = [touches anyObject]; CGPoint pnt =[touch locationInView:self.view]; changeView.center=CGPointMake(changeView.center.x-fromPoint.x+pnt.x, changeView.center.y-fromPoint.y+pnt.y); [clearImage setBounds:CGRectMake(0-changeView.frame.origin.x, 0-changeView.frame.origin.y, clearImage.frame.size.width, clearImage.frame.size.height)]; fromPoint=pnt; } } -(void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event { [screenShotButton setHidden:NO]; left=top=right=bottom=NO; shouldExpand=NO; fromPoint=CGPointZero; toPoint=CGPointZero; shouldChange=NO; } - (IBAction)takeScreenShot:(id)sender { [screenShotButton setHidden:YES]; UIGraphicsBeginImageContext(self.view.frame.size); CGContextRef context = UIGraphicsGetCurrentContext(); CGContextScaleCTM(context, 1.0, 1.0); [self.view.layer renderInContext:context]; UIImage *img = UIGraphicsGetImageFromCurrentImageContext(); UIGraphicsEndImageContext(); NSString *docPath = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) objectAtIndex:0]; NSString *filePath = [NSString stringWithFormat:@"%@/1.png",docPath]; CGRect cutRect = changeView.frame; CGImageRef imgRef = CGImageCreateWithImageInRect([img CGImage], cutRect); CFURLRef url = (__bridge CFURLRef)[NSURL fileURLWithPath:filePath]; CGImageDestinationRef destination = CGImageDestinationCreateWithURL(url, kUTTypePNG, 1, NULL); CGImageDestinationAddImage(destination, imgRef, nil); CFRelease(imgRef); if (!CGImageDestinationFinalize(destination)) { NSLog(@"Failed to write image to %@", filePath); } img=nil; imgRef=nil; CFRelease(destination); [screenShotButton setHidden:NO]; [changeView setHidden:NO]; } Just, logic mattered here!!
回答3:
Why dont you do it like this only:
- Create a imageview set its alpha to make it semitransparent
- Then just crop the part of the image that you want to be fully transparent and create a new imageview with alpha = 1 and set that cropped image in it only above the semi-transparent imageview :)
回答4:
I think you maybe be able to change the outside of selected rectangle. As for below image, you should 4 alphas of 4 rectangles. For example, at first you set white windows background color, then the 4 alpas of rectangles set to 0.5.
I think you would'd better use CALayer instead of UIView.
I wish my advice help your alittle.
回答5:
I think u can use CGContext
void CGContextDrawRadialGradient( CGContextRef context, CGGradientRef gradient, CGPoint startCenter, CGFloat startRadius, CGPoint endCenter, CGFloat endRadius, CGGradientDrawingOptions options ); see link below CGContext reference or CGGradient reference
回答6:
A simple method
1:Create a image in photoshop with the alpha values which you have specified. 2:Place the new imageview over your image . 3:If you want to move the transparent box ,change the image frame. 4:If you want to expand you just change the size of upper image. 来源：https://stackoverflow.com/questions/11792563/can-a-particular-rect-of-uiview-have-different-alpha