HandyIPhoneCodeSnippets

slerp has a whole mess of handy snippets: http://phonedev.tumblr.com

Take a screen shot

Thanks to Erica Sadun, I believe.

@implementation UIView (Snapshot)

(void)saveSnapshot { CGRect bounds; int err = 0, i; CGImageRef image = nil; char path[ 32 ]; CGContextRef pdfContext = nil; struct stat sb; CFStringRef string = nil; CFURLRef url = nil;

bounds = [self bounds];

for ( i = 0; i < 100; ++i ) { snprintf( path, sizeof(path), “/tmp/snapshot_%d.pdf”, i ); if ( stat( path, &sb ) == -1 ) break; }

if ( ! ( string = CFStringCreateWithCString( nil, path, kCFStringEncodingASCII ) ) ) err = 1; if ( ! err && ! ( image = [self createSnapshotWithRect: bounds] ) ) err = 1; if ( ! err && ! ( url = CFURLCreateWithFileSystemPath( nil, string, kCFURLPOSIXPathStyle, 0 ) ) ) err = 1; if ( ! err && ! ( pdfContext = CGPDFContextCreateWithURL( url, &bounds, nil ) ) ) err = 1;

if ( ! err ) { CGContextBeginPage( pdfContext, &bounds ); CGContextDrawImage( pdfContext, bounds, image ); CGContextEndPage( pdfContext ); CGContextFlush( pdfContext ); }

if ( pdfContext ) CGContextRelease( pdfContext ); if ( url ) CFRelease( url ); if ( image ) CGImageRelease( image ); if ( string ) CFRelease( string ); }

@end

Subclassing UIKit

To see what the rest of UIKit is expecting from your subclass, you can log calls to respondsToSelector: and the like.

(BOOL)respondsToSelector:(SEL)selector { NSLog(@”respondsToSelector: %s”, selector); return [super respondsToSelector:aSelector]; }
(NSMethodSignature*)methodSignatureForSelector:(SEL)selector { NSLog(@”methodSignatureForSelector: %s”, selector); return [super methodSignatureForSelector:selector]; }
(void)forwardInvocation:(NSInvocation*)invocation { NSLog(@”forwardInvocation: %s”, [invocation selector]); [super forwardInvocation:anInvocation]; }

If you use a function that returns a float or a double, you’ll get a linker error on the function objc_msgSend_fpret. Here’s a standin until the toolchain is fixed:

double objc_msgSend_fpret(id self, SEL op, …) { Method method = class_getInstanceMethod(self->isa, op); int numArgs = method_getNumberOfArguments(method);

if(numArgs == 2) {
	double (*imp)(id, SEL);
	imp = (double (*)(id, SEL))method->method_imp;
	return imp(self, op);
} else if(numArgs == 3) {
	// FIXME: this code assumes the 3rd arg is 4 bytes
	va_list ap;
	va_start(ap, op);
	double (*imp)(id, SEL, void *);
	imp = (double (*)(id, SEL, void *))method->method_imp;
	return imp(self, op, va_arg(ap, void *));
}

// FIXME: need to work with multiple arguments/types
fprintf(stderr, "ERROR: objc_msgSend_fpret, called on <%s %p> with selector %s, had to return 0.0\n", object_getClassName(self), self, sel_getName(op));
return 0.0;	 }

Update: http://www.tuaw.com/2007/09/04/iphone-coding-using-the-slider/ says that this is no longer necessary as of the v.20 toolchain.

CocoaDev