I have taken a UiView subclass but it's background color is not changing
This class I am using these method
- (id)initWithFrame:(CGRect)frame
{
self = [super initWithFrame:CGRectMake(50, 80, 200, 200)];
if (self)
{
// Initialization code
}
return self;
}
- (void)drawRect:(CGRect)rect{
CGContextRef context = UIGraphicsGetCurrentContext();
[[UIColor darkGrayColor]setFill];
CGContextClearRect(context, rect);
CGContextSetLineWidth(context, 2.0);
CGContextBeginPath(context);
CGContextSetStrokeColorWithColor(context, [UIColor orangeColor].CGColor);
CGContextMoveToPoint(context, 1, 1);
CGContextAddLineToPoint(context, 100, 100);
CGContextStrokePath(context); // and draw
}
I am calling this class to main view controller
Newclass *obj =[[Newsclass alloc]init];
obj.backgroundColor =[UIColor redColor];
[self.view addsubview :obj];
but background color by default show black color. It is not changing
if i implemented background-color code init with frame method or
draw rect method than not changing.
if i code it
- (id)initWithCoder:(NSCoder*)aDecoder
than it's method not called
please suggest me UIview subclass black background color how to change
First of all, you should do the color part in UIView file.
if (self = [super initWithFrame:CGRectMake(220,60, 100, 300)])
{
self.backgroundColor =[UIColor greenColor];
}
how ever you don't need to do in this case... ;)
it will definitely change your background color. But what happens next is that Draw rect method is called ,your color is no more visible as the draw rect method draws a view above it (whatever you draw in that method).
- (void)drawRect:(CGRect)rect
{
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextSetStrokeColorWithColor(context, [UIColor blueColor].CGColor);
CGRect rectangle = CGRectMake(0,0,200,300);
CGContextSetFillColorWithColor(context, [UIColor redColor].CGColor);
CGContextFillRect(context, rectangle);
}
You just cannot directly set the background color of cgcontext, you have to fill that context with color.
please make sure that you replace rectangle by rectangular frame of your view. It works like a charm for me.
Hey I am trying to add a shadow to all UINavigationBars in my project. I have tried a number of things recommended on this site and on other internet tutorials but have had no luck in getting a shadow to stick. I have tried putting it in using a shadow image I have created in photoshop, and calling the following in the main appDelegate:
[[UINavigationBar appearance] setShadowImage:[UIImage imageNamed:#"shadowTest.png"]];
I have subclassed the UINavigationBar out and tried to assign the property from within the class inside the awakeFromNib method and still nothing. I then tried to manually create the shadow with <QuartzCore/QuartzCore.h> image framework but nothing happened. I am using the subclass to override the drawRect method, could this be causing my problem? Here is the UINavigationBar class with my latest attempt at getting the shadow to stick.
#import "BasicNavigationBar.h"
#implementation BasicNavigationBar
- (id)initWithFrame:(CGRect)frame
{
self = [super initWithFrame:frame];
if (self)
{
// Initialization code
}
return self;
}
- (void)awakeFromNib
{
[super awakeFromNib];
// draw shadow
self.layer.masksToBounds = NO;
self.layer.shadowOffset = CGSizeMake(0, 3);
self.layer.shadowOpacity = 1.0;
self.layer.shadowColor = [UIColor blackColor].CGColor;
self.layer.shadowPath = [UIBezierPath bezierPathWithRect:self.bounds].CGPath;
}
- (void)drawRect:(CGRect)rect
{
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextSetFillColorWithColor(context, [UIColor whiteColor].CGColor);
CGContextFillRect(context, rect);
}
#end
setShadowImage doesn't work if you don't set the backgroundImage, too.
For a custom shadow image to be shown, a custom background image must also be set with the setBackgroundImage:forBarMetrics: method. If the default background image is used, then the default shadow image will be used regardless of the value of this property.
I'm drawing text in -drawRect with this method:
[someText drawInRect:rect withFont:font lineBreakMode:someLineBreakMode alignment:someAlignment];
I just want to draw the outline but not the fill!
I've found that I can set CGContextSetFillColorWithColor and just provide an fully transparent color. But I fear this has bad performance impact because probably it does all the heavy drawing work behind the scenes with a transparent color.
Is there a way to just disable the fill-drawing if only outline-drawing is wanted?
Have you tried using kCGTextFillStroke? This might work easily. To use it, just override drawTextInRect
- (void)drawTextInRect:(CGRect)rect {
CGSize shadowOffset = self.shadowOffset;
UIColor *textColor = self.textColor;
CGContextRef c = UIGraphicsGetCurrentContext();
CGContextSetLineWidth(c, 1);
CGContextSetLineJoin(c, kCGLineJoinRound);
CGContextSetTextDrawingMode(c, kCGTextStroke);
self.textColor = [UIColor whiteColor];
[super drawTextInRect:rect];
CGContextSetTextDrawingMode(c, kCGTextFill);
self.textColor = textColor;
self.shadowOffset = CGSizeMake(0, 0);
[super drawTextInRect:rect];
self.shadowOffset = shadowOffset;
}
EDIT: This answer also appears in a previous incarnation of this question: How do I make UILabel display outlined text?
I am trying to get a transparent background in CG but it keeps coming out black.
I have the following code:
- (id)initWithFrame:(CGRect)frame {
if ((self = [super initWithFrame:frame])) {
DLog(#">>> Alloc: DrawingCanvas [0x%X]", (unsigned int)self);
[self setOpaque:NO];
[self setBackgroundColor:[UIColor clearColor]];
}
return self;
}
- (void) drawRect:(CGRect)rect
{
CGContextRef context = UIGraphicsGetCurrentContext();
CGRect frame = rect;
int counter = 3;
CGContextClearRect(context, frame);
CGContextSetFillColorWithColor(context, [UIColor clearColor].CGColor);
CGContextFillRect(context, frame);
}
How do I get this code to show a transparent background?
With that setup and as long as you don't set clearsContextBeforeDrawing to NO, the background should already be transparent when your drawRect: method is called. Remove the CGContextClearRect and other drawing calls.
You could simply remove these lines :
CGContextClearRect(context, frame);
CGContextSetFillColorWithColor(context, [UIColor clearColor].CGColor);
CGContextFillRect(context, frame);
As long as you have set opaque to NO and clearColor as backgroundColor everything should be fine.
Be careful when drawing since your other drawing code may fill the background entirely (take care of [path fill] things in a non-clipped context).
I had this same problem and the solution was to set the backgroundColor property of the UIView which I was drawing in, from the parent view's class. I didn't need any code to clear the background in the UIView's class where the drawing happens.
myDrawingView.backgroundColor = [UIColor clearColor];
I am still struggling with drawing a line with CGContext. I have actually go to line to draw, but now I need the background of the Rect to be transparent so the existing background shows thru. Here's my test code:
(void)drawRect:(CGRect)rect
{
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextSetFillColorWithColor(context, [UIColor clearColor].CGColor);
CGContextSetAlpha(context,0.0);
CGContextFillRect(context, rect);
CGContextSetStrokeColorWithColor(context, [UIColor whiteColor].CGColor);
CGContextSetLineWidth(context, 5.0);
CGContextMoveToPoint(context, 100.0,0.0);
CGContextAddLineToPoint(context,100.0, 100.0);
CGContextStrokePath(context);
}
Any ideas?
After UIGraphicsGetCurrentContext() call CGContextClearRect(context,rect)
Edit:
Alright, got it.
Your custom view with the line should have the following:
- (id)initWithFrame:(CGRect)frame {
if (self = [super initWithFrame:frame]) {
[self setBackgroundColor:[UIColor clearColor]];
}
return self;
}
- (void)drawRect:(CGRect)rect {
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextClearRect(context, rect);
CGContextSetStrokeColorWithColor(context, [UIColor whiteColor].CGColor);
CGContextSetLineWidth(context, 5.0);
CGContextMoveToPoint(context, 100.0,0.0);
CGContextAddLineToPoint(context,100.0, 100.0);
CGContextStrokePath(context);
}
My test used this as a very basic UIViewController:
- (void)viewDidLoad {
[super viewDidLoad];
UIImageView *v = [[UIImageView alloc] initWithFrame:self.view.bounds];
[v setBackgroundColor:[UIColor redColor]];
[self.view addSubview:v];
TopView *t = [[TopView alloc] initWithFrame:self.view.bounds];
[self.view addSubview:t];
[v release];
[t release];
}
Easy way:
- (id)initWithFrame:(CGRect)frame
{
if ((self = [super initWithFrame:frame]))
{
self.opaque = NO;
}
return self;
}
- (void)drawRect:(CGRect)rect
{
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextClearRect(context, rect);
//your code
}
Init a context with opaque == false, Swift 3
UIGraphicsBeginImageContextWithOptions(size, false, UIScreen.main.scale)
opaque
A Boolean flag indicating whether the bitmap is opaque. If you know the bitmap is fully opaque, specify true to ignore the alpha channel and optimize the bitmap’s storage. Specifying false means that the bitmap must include an alpha channel to handle any partially transparent pixels.
This is what worked for me with a UIImage which had been manually added using InterfaceBuilder.
- (id)initWithCoder:(NSCoder *)aDecoder {
if(self = [super initWithCoder:aDecoder]) {
self.backgroundColor = [UIColor clearColor];
}
return self;
}
-(void)drawRect:(CGRect)rect
{
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextSetStrokeColorWithColor(context, [UIColor whiteColor].CGColor);
CGContextSetLineWidth(context, 5.0);
CGContextMoveToPoint(context, 100.0,0.0);
CGContextAddLineToPoint(context,100.0, 100.0);
CGContextStrokePath(context);
}
David Kanarek's answer only works when you're manually creating your own UIImageView. If you've created a UIView and manually added it via Interface Builder then you will need a different approach like this calling the initWithCoder method instead.
I have the same problem, then I find it is.
I overwrite the init Method is -(id)initWithFrame:(CGRect)rect.
In this method self.background = [UIColor clearColor];
but i use this view in xib file !!! That will call the init method is
-(id)initWithCoder:(NSCoder*)aDecoder;
So overwrite all the init Method and setup BackgroundColor will work OK.
CGContextClearRect(context,rect)
If the provided context is a window or bitmap context, Quartz effectively clears the rectangle. For other context types, Quartz fills the rectangle in a device-dependent manner. However, you should not use this function in contexts other than window or bitmap contexts.
you can create a image context with this code:
cacheContext = CGBitmapContextCreate (cacheBitmap, size.width, size.height, 8, bitmapBytesPerRow, CGColorSpaceCreateDeviceRGB(), kCGImageAlphaPremultipliedLast);
CGContextSetRGBFillColor(cacheContext, 0, 0, 0, 0);
CGContextFillRect(cacheContext, (CGRect){CGPointZero, size});
the key is kCGImageAlphaPremultipliedLast.
Having trouble understanding the question here, but if you're unable to have a "background" UIView show through a "top" view into which you're drawing, one solution is topView.backgroundColor = [UIColor clearColor]; I was having (I think) this same problem and this solved it for me.