Drag-and-Drop(Chapter 23 of Cocoa Programming for Mac OS X)

#import "BigLetterView.h"


@implementation BigLetterView

- (NSDragOperation)draggingSourceOperationMaskForLocal:(BOOL)isLocal
{
    return NSDragOperationCopy | NSDragOperationDelete;
}

- (NSDragOperation)draggingUpdated:(id <NSDraggingInfo>)sender
{
    NSDragOperation op = [sender draggingSourceOperationMask];
    NSLog(@"operation mask = %d", op);
    if ([sender draggingSource] == self) 
    {
        return NSDragOperationNone;
    }
    
    return NSDragOperationCopy;
}

- (void)mouseDown:(NSEvent *)event
{
    [event retain];
    [mouseDownEvent release];
    mouseDownEvent = event;
}

- (void)mouseDragged:(NSEvent *)event
{
    NSPoint down = [mouseDownEvent locationInWindow];
    NSPoint drag = [event locationInWindow];
    float distance = hypot(down.x-drag.x, down.y-drag.y);
    if(distance < 3)
    {
        return;
    }
    
    if([string length] == 0)
    {
        return;
    }
    
    NSSize s = [string sizeWithAttributes:attributes];
    NSImage *anImage = [[NSImage alloc] initWithSize:s];
    NSRect imageBounds;
    imageBounds.origin = NSZeroPoint;
    imageBounds.size = s;
    
    [anImage lockFocus];
    [self drawStringCenteredIn:imageBounds];
    [anImage unlockFocus];
    
    NSPoint p = [self convertPoint:down fromView:nil];
    
    p.x = p.x - s.width/2;
    p.y = p.y - s.height/2;
    
    NSPasteboard *pb = [NSPasteboard pasteboardWithName:NSDragPboard];
    
    [self writeToPasteboard:pb];
    [self dragImage:anImage at:p offset:NSMakeSize(0, 0) event:mouseDownEvent pasteboard:pb source:self slideBack:YES];
    [anImage release];
}

- (void)draggedImage:(NSImage *)image beganAt:(NSPoint)screenPoint operation:(NSDragOperation)operation
{
    if(operation == NSDragOperationDelete)
    {
        [self setString:@""];
    }
}

- (void)writeToPasteboard:(NSPasteboard *)pb
{
    [pb declareTypes:[NSArray arrayWithObject:NSStringPboardType] owner:self];
    [pb setString:string forType:NSStringPboardType]; 
}

- (BOOL)readFromPasteboard:(NSPasteboard *)pb
{
    NSArray *types = [pb types];
    if([types containsObject:NSStringPboardType])
    {
        NSString *value = [pb stringForType:NSStringPboardType];
        if([value length] == 1)
        {
            [self setString:value];
            return YES;
        }
    }
    
    return NO;
}

- (IBAction)cut:(id)sender
{
    [self copy:sender];
    [self setString:@""];
}

- (IBAction)copy:(id)sender
{
    NSPasteboard *pb = [NSPasteboard generalPasteboard];
    [self writeToPasteboard:pb];
}

- (IBAction)paste:(id)sender
{
    NSPasteboard *pb = [NSPasteboard generalPasteboard];
    if (![self readFromPasteboard:pb]) 
    {
        NSBeep();
    }
}

- (IBAction)savePDF:(id)sender
{
    NSSavePanel *panel = [NSSavePanel savePanel];
    [panel setRequiredFileType:@"pdf"];
    [panel beginSheetForDirectory:nil file:nil modalForWindow:[self window] modalDelegate:self didEndSelector:@selector(didEnd:returnCode:contextInfo:) contextInfo:NULL];
}

- (void)prepareAttributes
{
    attributes = [[NSMutableDictionary alloc] init];
    [attributes setObject:[NSFont fontWithName:@"Helvetica" size:75] forKey:NSFontAttributeName];
    [attributes setObject:[NSColor redColor] forKey:NSForegroundColorAttributeName];
}

- (void)didEnd:(NSSavePanel    *)sheet returnCode:(int)code contextInfo:(void *)contextInfo
{
    if(code != NSOKButton)
    {
        return;
    }
    
    NSRect r = [self bounds];
    NSData *data = [self dataWithPDFInsideRect:r];
    NSString *path = [sheet filename];
    NSError *error;
    BOOL successful = [data writeToFile:path options:0 error:&error];
    if (!successful) 
    {
        NSAlert *a = [NSAlert alertWithError:error];
        [a runModal];
    }
}

- (id)initWithFrame:(NSRect)frameRect
{
    if(![super initWithFrame:frameRect])
    {
        return nil;
    }
    
    NSLog(@"initializing view");
    [self prepareAttributes];
    bgColor = [[NSColor yellowColor] retain];
    string = @" ";
    [self registerForDraggedTypes: [NSArray arrayWithObject:NSStringPboardType]];
    return self;
}

- (void)dealloc
{
    [bgColor release];
    [string release];
    [attributes release];
    [super dealloc];
}

- (void)drawRect:(NSRect)dirtyRect
{
    NSRect bounds = [self bounds];
    if(highlighted)
    {
        NSGradient *gr;
        gr = [[NSGradient alloc] initWithStartingColor:[NSColor whiteColor] endingColor:bgColor];
        [gr drawInRect:bounds relativeCenterPosition:NSZeroPoint];
        [gr release];
    }
    else 
    {
        [bgColor set];
        [NSBezierPath fillRect:bounds];
    }
    
    [self drawStringCenteredIn:bounds];
    
    if([[self window] firstResponder] == self)
    {
        [[NSColor keyboardFocusIndicatorColor] set];
        [NSBezierPath setDefaultLineWidth:4.0];
        [NSBezierPath strokeRect:bounds];
    }
}

- (BOOL)isOpaque
{
    return YES;
}

- (BOOL)acceptsFirstResponder
{
    NSLog(@"Accepting");
    return YES;
}

- (BOOL)resignFirstResponder
{
    NSLog(@"Resigning");
    [self setNeedsDisplay:YES];
    return YES;
}

- (BOOL)becomeFirstResponder
{
    NSLog(@"Becoming");
    [self setNeedsDisplay:YES];
    return YES;
}

- (void)keyDown:(NSEvent *)theEvent
{
    [self interpretKeyEvents:[NSArray arrayWithObject:theEvent]];
}

- (void)insertText:(NSString *)input
{
    [self setString:input];
}

- (void)insertTab:(id)sender
{
    [[self window] selectKeyViewPrecedingView:self];
}

- (void)deleteBackward:(id)sender
{
    [self setString:@" "];
}

#pragma mark Accessors

- (void)setBgColor:(NSColor *)c
{
    [c retain];
    [bgColor release];
    bgColor = c;
    [self setNeedsDisplay:YES];
}

- (NSColor *)bgColor
{
    return bgColor;
}

- (void)drawStringCenteredIn:(NSRect)r
{
    NSSize strSize = [string sizeWithAttributes:attributes];
    NSPoint strOrigin;
    strOrigin.x = r.origin.x + (r.size.width - strSize.width)/2;
    strOrigin.y = r.origin.y + (r.size.height - strSize.height)/2;
    [string drawAtPoint:strOrigin withAttributes:attributes];
}

- (void)setString:(NSString *)c
{
    c = [c copy];
    [string release];
    string = c;
    NSLog(@"The string is now %@", string);
    [self setNeedsDisplay:YES];
}

- (NSString *)string
{
    return string;
}

#pragma mark Dragging Destination

- (NSDragOperation)draggingEntered:(id <NSDraggingInfo>)sender
{
    NSLog(@"draggingEntered:");
    if ([sender draggingSource] == self) 
    {
        return NSDragOperationNone;
    }
    highlighted = YES;
    [self setNeedsDisplay:YES];
    return NSDragOperationCopy;
}

- (void)draggingExited:(id <NSDraggingInfo>)sender
{
    NSLog(@"draggingExited:");
    highlighted = NO;
    [self setNeedsDisplay:YES];
}

- (BOOL)prepareForDragOperation:(id <NSDraggingInfo>)sender
{
    return YES;
}

- (BOOL)performDragOperation:(id <NSDraggingInfo>)sender
{
    NSPasteboard *pb = [sender draggingPasteboard];
    if (![self readFromPasteboard:pb]) 
    {
        NSLog(@"Error: Could not read from draggin pasteboard");
        return NO;
    }
    return YES;
}

- (void)concludeDragOperation:(id <NSDraggingInfo>)sender
{
    NSLog(@"concludeDragOperation");
    highlighted = NO;
    [self setNeedsDisplay:YES];
}
@end