Draw text in circle overlay

问题

I'm trying to draw some circle overlays containing text on MKMapView. I have subclassed the MKCircleView, in which I put the following (based on this), but the text does not appear. The circles show up correctly. (Also tried the first response's solution, same result).

-(void)drawMapRect:(MKMapRect)mapRect zoomScale:(MKZoomScale)zoomScale inContext:(CGContextRef)context {
   [super drawMapRect:mapRect zoomScale:zoomScale inContext:context];
   NSString * t= @"XXXXX\nXXXX" ;
   UIGraphicsPushContext(context);
   CGContextSaveGState(context); 
   [[UIColor redColor] set];
   CGRect overallCGRect = [self rectForMapRect:[self.overlay boundingMapRect]];
   NSLog(@"MKC :  %lf, %lf ----> %lf , %lf ", mapRect.origin.x ,mapRect.origin.y , overallCGRect.origin.x, overallCGRect.origin.y);
   [t drawInRect:overallCGRect withFont:[UIFont fontWithName:@"Arial" size:10.0] lineBreakMode:UILineBreakModeClip alignment:UITextAlignmentCenter];
   CGContextRestoreGState(context);
   UIGraphicsPopContext();
}

When debugging, I get values like these

MKC :  43253760.000000, 104071168.000000 ----> 1.776503 , 1.999245 
MKC :  43253760.000000, 104071168.000000 ----> -1.562442 , -2.043090

Are they normal ? What am I missing ?

Thanks.

回答1:

I believe your code is working and the problem is that the text is not being scaled properly making it invisible.

Scale the font size based on the zoomScale using the MKRoadWidthAtZoomScale function:

[t drawInRect:overallCGRect withFont:[UIFont fontWithName:@"Arial" 
    size:(10.0 * MKRoadWidthAtZoomScale(zoomScale))] 
    lineBreakMode:UILineBreakModeClip alignment:UITextAlignmentCenter];

Also be sure to use a text color that's different from the underlying circle's color.

Note that using drawInRect will result in the text being restricted to inside the circle and may get truncated. If you want to always show all the text, you could use drawAtPoint instead.

回答2:

Combining the answers here and updating for IOS7:

-(void)drawMapRect:(MKMapRect)mapRect zoomScale:(MKZoomScale)zoomScale inContext:(CGContextRef)context
{
    [super drawMapRect:mapRect zoomScale:zoomScale inContext:context];

    UIGraphicsPushContext(context);
    CGContextSaveGState(context);
    [[UIColor blueColor] set];

    NSDictionary *fontAttributes = @{NSFontAttributeName:[UIFont systemFontOfSize:10.0f * MKRoadWidthAtZoomScale(zoomScale)]};
    CGSize size = [[[self overlay] title] sizeWithAttributes:fontAttributes];
    CGFloat height = ceilf(size.height);
    CGFloat width  = ceilf(size.width);

    CGRect circleRect = [self rectForMapRect:[self.overlay boundingMapRect]];
    CGPoint center = CGPointMake(circleRect.origin.x + circleRect.size.width /2, circleRect.origin.y + circleRect.size.height /2);
    CGPoint textstart = CGPointMake(center.x - width/2, center.y - height /2 );

    [[[self overlay] title] drawAtPoint:textstart withAttributes:fontAttributes];

    CGContextRestoreGState(context);
    UIGraphicsPopContext();
}

回答3:

It is most likely that your text is drawn to a rectangle which is not visible.

First thing I would do is try printing the values as %f instead of %lf, as those values look crazy. You should also print out the .size.width and .size.height for the two rects (mapRect and overallCGRect).

If that doesn't lead you to a sensible rectangle definition, then try defining a CGRect yourself like CGRectMake(0,0,100,20) and see if the text draws.

You can also try simply drawing a filled rectangle to the same overallCGRect that you are drawing your text into.

来源：https://stackoverflow.com/questions/7825220/draw-text-in-circle-overlay