CGContextRef gives Error

i am using CGContextRef to draw one horizontal bar and above-below of bar i am displaying text using drawInRect method of NSString.Here is code:

        CGContextRef context = UIGraphicsGetCurrentContext();//set frame for bar
        CGRect frame;
        frame.origin.x = prevWidth;
        frame.origin.y = heightBar;
        frame.size.height = heightOfBar;
        frame.size.width = 10;

        UIColor* color = [ColorArray objectAtIndex:i];
        CGContextSetFillColorWithColor(context, color.CGColor);
        CGContextSetLineWidth(context, lineWidth);
        CGContextSetStrokeColorWithColor(context, borderColor.CGColor);

        CGContextFillRect(context, frame);
        CGContextStrokeRect(context, frame);
        [nameString drawInRect:frame1 withFont:font lineBreakMode:NSLineBreakByClipping alignment:NSTextAlignmentCenter];

When i call second time it gives me error like:<Error>: CGContextSetFillColorWithColor: invalid context 0x0.Please help me.Thanking you.

The error says the context is invalid .So i suppose calling the second time means you are calling the method directly i guess.

As per docs

The current graphics context is nil by default. Prior to calling its drawRect: method, view objects push a valid context onto the stack, making it current.

The context will be valid only in drawRect: method.You need to call -setNeedsDisplay on the UIView to update the contents