This is a program I'm writing (myself as opposed to copying someone else's and thus not learning) as part of the ObjectiveC and Cocoa learning curve. I want to draw simple shapes on a NSView (limiting it to ovals and rectangles for now). The idea is that I record each NSBezierPath to an NSMutableArray so I can also investigate/implement saving/loading, undo/redo. I have a canvas, can draw on it as well as 2 buttons that I use to select the tool. To handle the path I created another object that can hold a NSBezierPath, color values and size value for each object drawn. This is what I want to store in the array. I use mouseDown/Dragged/Up to get coordinates for the drawing path. However, this is where things go wonky. I can instantiate the object that is supposed to hold the path/color/etc. info but, when I try to change an instance variable, the app crashes with no useful message in the debugger. I'll try to keep my code snippets short but tell me if I need to include more. The code has also degenerated a little from me trying so many things to make it work.
Project: Cocoa document based app
I have the following .m/.h files
MyDocument:NSDocument - generated by XCode
DrawnObject:NSObject - deals with the drawn object i.e. path, color, type (oval/rect) and size
Canvas:NSView - well, shows the drawing, deals with the mouse and buttons
Canvas is also responsible for maintaining a NSMutableArray of DrawnObject objects.
DrawnObject.h looks like this:
#import <Foundation/Foundation.h>
//The drawn object must know what tool it was created with etc as this needs to be used for generating the drawing
#interface DrawnObject : NSObject {
NSBezierPath * aPath;
NSNumber * toolType;//0 for oval, 1 for rectangular etc....
float toolSize;
struct myCol{
float rd;
float grn;
float blu;
float alp;
} toolColor;
}
-(void)setAPath:(NSBezierPath *) path;
-(NSBezierPath *)aPath;
#property (readwrite,assign) NSNumber * toolType;
-(float)toolSize;
-(void)setToolSize:(float) size;
-(struct myCol *)toolColor;
-(void)setCurrentColor:(float)ref:(float)green:(float)blue:(float)alpha;
#end
Canvas.h looks like this
#import
#import "drawnObject.h"
#interface Canvas : NSView {
NSMutableArray * myDrawing;
NSPoint downPoint;
NSPoint currentPoint;
NSBezierPath * viewPath;//to show the path as the user drags the mouse
NSNumber * currentToolType;
BOOL mouseUpFlag;//trying a diff way to make it work
BOOL mouseDrag;
}
-(IBAction)useOval:(id)sender;
-(IBAction)useRect:(id)sender;
-(IBAction)showTool:(id)sender;
-(NSRect)currentRect;
-(NSBezierPath *)createPath:(NSRect) aRect;
-(void)setCurrentToolType:(NSNumber *) t;
-(NSNumber *)currentToolType;
#end
In the Canvas.m file there are several functions to deal with the mouse and NSView/XCode also dropped in -(id)initWithFrame:(NSRect)frame and -(void)drawRect:(NSRect)rect Originally I use mouseUp to try to insert the new DrawnObject into the array but that caused a crash. So, now I use two BOOL flags to see when the mouse was released (clunky but I'm trying....)in drawRect to insert into the array. I've included the method below and indicated where it causes the app to fail:
- (void)drawRect:(NSRect)rect { //This is called automatically
// Drawing code here.
//NSLog(#"Within drawRect tool type is %d", [self currentTool]);
NSRect bounds = [self bounds];
NSRect aRect = [self currentRect];
viewPath = [self createPath:aRect];
//the createPath method uses the tool type to switch between oval and rect bezier curves
if(mouseUpFlag==YES && mouseDrag==YES){
mouseDrag=NO;
//Create a new drawnObject here
DrawnObject * anObject = [[DrawnObject alloc]init];//- WORKS FINE UP TO HERE
NSLog(#"CREATED NEW drawnObject");
[anObject setAPath:viewPath]; //- INSTANT APP DEATH!!!!
NSLog(#"Set a path in drawnObject");
[anObject setToolType:[[NSNumber alloc]initWithInt:5]];
NSLog(#"Set toolType in DrawnObject");
[anObject setToolType:currentToolType];
[myDrawing addObject:anObject];
NSLog(#"Added Object");
}
[[NSColor colorWithCalibratedRed:0.0 green:0.9 blue:0.0 alpha:0.5]set];
[NSBezierPath fillRect:bounds];
[[NSColor lightGrayColor]set];
[viewPath stroke]; //This is so the user can see where the drawing is being done
//Now, draw the paths in the array
[[NSColor blueColor]set];
for(DrawnObject * indexedObject in myDrawing){
[[indexedObject aPath] stroke];//This will do the actual drawing of ALL objects
}
}
I guess this has something to do with object scope or something but I just can not figure it out. As I said, as I've tried things the code has sort of undergone an metamorphosis, sadly not for the better. Like those BOOLS etc.
HELP! Any clever people out there, point me in the right direction please!
ADDED THIS ON:
-(NSBezierPath *)createPath:(NSRect) aRect
{
NSBezierPath * tempPath;
//I need to know what tool
switch(0){ //temporary - this would use the toolType as a selector
case 0:
tempPath = [NSBezierPath bezierPathWithOvalInRect:aRect];
break;
case 1:
tempPath = [NSBezierPath bezierPathWithRect:aRect];
break;
default:
tempPath = [NSBezierPath bezierPathWithOvalInRect:aRect];
break;
}
return tempPath;
}
You said your init method was:
-(void)init {
[super init];
//set default color = black
toolColor.rd=1.0;
toolColor.grn=1.0;
toolColor.blu=1.0;
toolColor.alp=1.0;
//set default size
toolSize=0.8;
//set default toolType
toolType=0;
//oval
NSLog(#"Init %#",self);
}
This is definitely wrong; read up on how to create an init method in the Obj-C guide or by reading sample code. Here's what it should look like:
-(id)init {
if (self = [super init]) {
//set default color = black
toolColor.rd=1.0;
toolColor.grn=1.0;
toolColor.blu=1.0;
toolColor.alp=1.0;
//set default size
toolSize=0.8;
//set default toolType
toolType=0;
//oval
NSLog(#"Init %#",self);
}
return self;
}
By not returning anything from -init, you were preventing the object's creation. Good luck! :-)
Edit: Ashley beat me to it...
What do you mean by “crash”?
Does anything appear in the Debugger Console (⇧⌘R)?
Does a stack trace appear in the Debugger window?
If there's a stack trace, where in your code does it crash?
It just hangs. In the debugger I see:
[Session started at 2008-11-28 14:40:34 +1000.]
2008-11-28 14:40:36.157 CH18Challenge_try2[1893:10b] Mouse Down at (80.000000,285.000000)
2008-11-28 14:40:36.333 CH18Challenge_try2[1893:10b] Mouse Up at (166.000000,217.000000)
2008-11-28 14:40:36.348 CH18Challenge_try2[1893:10b] Init
2008-11-28 14:40:36.349 CH18Challenge_try2[1893:10b] CREATED NEW drawnObject
[Session started at 2008-11-28 14:40:36 +1000.]
Loading program into debugger…
GNU gdb 6.3.50-20050815 (Apple version gdb-962) (Sat Jul 26 08:14:40 UTC 2008)
Copyright 2004 Free Software Foundation, Inc.
GDB is free software, covered by the GNU General Public License, and you are
welcome to change it and/or distribute copies of it under certain conditions.
Type "show copying" to see the conditions.
There is absolutely no warranty for GDB. Type "show warranty" for details.
This GDB was configured as "i386-apple-darwin".Program loaded.
sharedlibrary apply-load-rules all
Attaching to program: `/Users/johan_kritzinger/Documents/Cocoa/CH18Challenge_try2/build/Debug/CH18Challenge_try2.app/Contents/MacOS/CH18Challenge_try2', process 1893.
(gdb)
Then I have to force quit to stop it.
We need to see the implementation of setAPath from DrawnObject.m. Also, for the "stack trace" look on the upper left of the debugger--it should list a stack of functions showing where in your code the crash is. Make sure you're running in Debug mode, not Release.
On the command line you can type print-object and you can
set a breakpoint in that line and step through it from there. It seems setAPath is somehow broken
Regards
Friedrich
What you have is not a crash. A crash is when a signal is raised (like EXC_BAD_ACCESS) or an uncaught exception.
What you have seems to be an infinite loop.
You need to use the pause button in the Debugger and see exactly where. I would guess that you have an infinite loop in your setAPath: method. You need to work out why this function is looping indefinitely.
Related
I come from a C/C++ background and am currently learning a bit about Cocoa and Objective-C.
I have a weird behavior involving lazy initialization (unless I'm mistaken) and feel like I'm missing something very basic.
Setup:
Xcode 10.1 (10B61)
macOS High Sierra 10.13.6
started from a scratch Cocoa project
uses Storyboard
add files TestMainView.m/.h
under the View Controller in main.storyboard, set the NSView custom class as TestMainView
tested under debug and release builds
Basically, I create an NSTextView inside a view controller to be able to write some text.
In TestMainView.m, I create the chain of objects programmatically as decribed here
There are two paths:
first one is enabled by setting USE_FUNCTION_CALL to 0, it makes the entire code run inside awakeFromNib().
second path is enabled by setting USE_FUNCTION_CALL to 1. It makes the text container and text view to be allocated from the function call addNewPage() and returns the text container for further usage.
First code path works just as expected: I can write some text.
However second code path just doesn't work because upon return, textContainer.textView is nil (textContainer value itself is totally fine).
What's more troubling though (and this is where I suspect lazy init to be the culprit) is that if I "force" the textContainer.textView value while inside the function call, then everything works just fine. You can try this by setting FORCE_VALUE_LOAD to 1.
It doesn't have to be an if(), it works with NSLog() as well. It even works if you set a breakpoint at the return line and use the debugger to print the value ("p textContainer.textView")
So my questions are:
is this related to lazy initialization ?
is that a bug ? is there a workaround ?
am I thinking about Cocoa/ObjC programming the wrong way ?
I really hope I am missing something here because I cannot be expected to randomly check variables here and there inside Cocoa classes, hoping that they would not turn nil. It even fails silently (no error message, nothing).
TestMainView.m
#import "TestMainView.h"
#define USE_FUNCTION_CALL 1
#define FORCE_VALUE_LOAD 0
#implementation TestMainView
NSTextStorage* m_mainStorage;
- (void)awakeFromNib
{
[super awakeFromNib];
m_mainStorage = [NSTextStorage new];
NSLayoutManager* layoutManager = [[NSLayoutManager alloc] init];
#if USE_FUNCTION_CALL == 1
NSTextContainer* textContainer = [self addNewPage:self.bounds];
#else
NSTextContainer* textContainer = [[NSTextContainer alloc] initWithSize:NSMakeSize(FLT_MAX, FLT_MAX)];
NSTextView* textView = [[NSTextView alloc] initWithFrame:self.bounds textContainer:textContainer];
#endif
[layoutManager addTextContainer:textContainer];
[m_mainStorage addLayoutManager:layoutManager];
// textContainer.textView is nil unless forced inside function call
[self addSubview:textContainer.textView];
}
#if USE_FUNCTION_CALL == 1
- (NSTextContainer*)addNewPage:(NSRect)containerFrame
{
NSTextContainer* textContainer = [[NSTextContainer alloc] initWithSize:NSMakeSize(FLT_MAX, FLT_MAX)];
NSTextView* textView = [[NSTextView alloc] initWithFrame:containerFrame textContainer:textContainer];
[textView setMaxSize:NSMakeSize(FLT_MAX, FLT_MAX)];
#if FORCE_VALUE_LOAD == 1
// Lazy init ? textContainer.textView is nil unless we force it
if (textContainer.textView)
{
}
#endif
return textContainer;
}
#endif
- (void)drawRect:(NSRect)dirtyRect {
[super drawRect:dirtyRect];
// Drawing code here.
}
#end
TestMainView.h
#import <Cocoa/Cocoa.h>
NS_ASSUME_NONNULL_BEGIN
#interface TestMainView : NSView
#end
NS_ASSUME_NONNULL_END
I am not familiar with cocoa that much but I think the problem is ARC (Automatic reference counting).
NSTextView* textView = [[NSTextView alloc] initWithFrame:containerFrame textContainer:textContainer];
In the .h file of NSTextContainer you can see NSTextView is a weak reference type.
So after returning from the function it gets deallocated
But if you make the textView an instance variable of TestMainView it works as expected.
Not really sure why it also works if you force it though. ~~(Maybe compiler optimisation?)~~
It seems forcing i.e calling
if (textContainer.textView) {
is triggering retain/autorelease calls so until the next autorelease drain call, textview is still alive.(I am guessing it does not get drained until awakeFromNib function returns). The reason why it works is that you are adding the textView to the view hierarchy(a strong reference) before autorelease pool releases it.
cekisakurek's answer is correct. Objects are deallocated if there is no owning (/"strong") reference to them. Neither the text container nor the text view have owning references to each other. The container has a weak reference to the view, which means that it's set to nil automatically when the view dies. (The view has an non-nilling reference to the container, which means you will have a dangling pointer in textView.textContainer if the container is deallocated while the view is still alive.)
The text container is kept alive because it's returned from the method and assigned to a variable, which creates an owning reference as long as that variable is in scope. The view's only owning reference was inside the addNewPage: method, so it does not outlive that scope.
The "force load" has nothing to do with lazy initialization; as bbum commented, that it "works" is most likely to be accidental. I strongly suspect it wouldn't in an optimized build.
Let me assure you that you do not need to go around poking properties willy-nilly in Cocoa programming. But you do need to consider ownership relations between your objects. In this case, something else needs to own both container and view. That can be your class here, via an ivar/property, or another object that's appropriate given the NSText{Whatever} API (which is not familiar to me).
I am learning OpenGL. To get an OpenGL context setup I was following the GlEssentials example from Apple. The GlContext is there locked in the draw method as follows:
- (void) drawView
{
[[self openGLContext] makeCurrentContext];
// We draw on a secondary thread through the display link
// When resizing the view, -reshape is called automatically on the main
// thread. Add a mutex around to avoid the threads accessing the context
// simultaneously when resizing
CGLLockContext([[self openGLContext] CGLContextObj]);
[m_renderer render];
CGLFlushDrawable([[self openGLContext] CGLContextObj]);
CGLUnlockContext([[self openGLContext] CGLContextObj]);
}
When I tried to call CGLLockContext with exactly the same arguments as above in my view class I the following error:
No matching function for call to 'CGLLockContext
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.9.sdk/System/Library/Frameworks/OpenGL.framework/Headers/OpenGL.h:111:17: Candidate function not viable: cannot convert argument of incomplete type 'void *' to 'CGLContextObj' (aka '_CGLContextObject *')
Quickly inserting a typecast fixed the issue:
CGLLockContext((CGLContextObj)[[self openGLContext] CGLContextObj]);
Question is why? In Apples example it works fine without this typecast.
Two thoughts:
1) Are you doing this inside a C++ or ObjC++ file? That whole “candidate function” thing sounds like C++ to me, but I don’t really know C++.
2) Are your compiler flags (especially warnings and errors) the same in your project files as they are in Apple’s sample project. (I took a quick look at Xcode 5’s compiler settings and nothing jumped out at me.)
I'm trying to get this code: http://code.google.com/p/switchcontrol/source/browse/trunk/code/AFSwitchControl.m compiling under Apple LLVM in Xcode 4.5.2. It works when compiled with LLVM/GCC, but crashes in the mouseDown method when switched to Apple LLVM on line 198:
NSRect knobRect = _AFSwitchControlKnobRectForInsetBackground(slotRect, _offset);
Because _offset is not set. It's suppose to be set in the bind method with this line:
[self setOffset:(CGFloat)[self state]];
But it appears that nothing is being set under LLVM for some reason. My binding call looks like:
[control bind:NSValueBinding toObject:self withKeyPath:#"isToggleSwitchOn" options:nil];
Any ideas why the control's state is not returning anything under LLVM? Thanks!
The problem is actually a few lines above, in the call to _AFSwitchControlPartRects.
- (void)mouseDown:(NSEvent *)event {
NSRect textRect, backgroundRect;
_AFSwitchControlPartRects([self bounds], &textRect, &backgroundRect);
NSRect slotRect = _AFSwitchControlInsetBackgroundRect(backgroundRect);
NSRect knobRect = _AFSwitchControlKnobRectForInsetBackground(slotRect, _offset);
The second argument to _AFSwitchControlPartRects, &textRect is a pointer to a rect.
However in the implementation of the function, that parameter is supposed to be a pointer to enough space for two rects.
NS_INLINE void _AFSwitchControlPartRects(NSRect bounds, NSRect *textRects, NSRect *backgroundRect) {
NSDivideRect(bounds, textRects, backgroundRect, NSWidth(bounds)/5.0, NSMinXEdge);
textRects[1] = _AFSwitchControlInsetTextRect(NSOffsetRect(textRects[0], NSWidth(*backgroundRect), 0));
textRects[0] = _AFSwitchControlInsetTextRect(textRects[0]);
When this writes to textRects[1], it's scribbling on -mouseDown's stack. Buffer overflow.
It looks to me like it's happening to clobber self, so the next dereference of self will die. This happens to be the use of _offset.
The context is that I am trying to plot a series of temperatures as a graph.
At the moment my application works as follows (as i understand it):
The application opens, openfile is used which initialises my document class this reads the modified csv file into an NSString "fileContents" which I then separate into an array of strings, each string containing the value without separaters or whitespace. As follows:
NSArray *temps = [fileContents componentsSeparatedByCharactersInSet: [NSCharacterSet characterSetWithCharactersInString:#"\n|\r"]];
After that I initialise my custom view, the TemperatureGraph class, and immediately pass it the array which becomes the currentlog seen in the code below. Instance id is current.
Finally I invoke:
[current drawpath];
Which is the instance method below:
- (void) drawpath
{
NSBezierPath *program = [NSBezierPath bezierPath];
NSPoint st = NSMakePoint(0, 0);
[program moveToPoint:st];
[program setLineWidth:10];
[program setLineCapStyle:NSRoundLineCapStyle];
[[NSColor blueColor] setStroke];
[program stroke];
NSUInteger a, b;
a = [currentlog count];
b = 0;
while (b <= a) {
NSPoint new;
float x;
x = 5 * b;
new = NSMakePoint(x, [[currentlog objectAtIndex:b] floatValue]);
[program lineToPoint:new];
[program stroke];
b += 6;
}
}
Why won't it work? Definition of won't work: Application compiles and runs but I have a blank window.
Also please point out any rookie errors that are in there but don't affect code, as I am still in the learning stages here.
Drawing doesn't happen unless you have an active graphics context. I'm assuming the drawpath method above is inside an NSView subclass - well in there you need to override a method called drawRect: - it may even have been added in as a stub when you made the subclass?
Cocoa calls this method when it is time for the view to draw itself. This means that, when it is being called, a graphics context will be set up and and drawing code you do will actually appear on the screen.
Simply call your drawpath method from inside drawRect: and you should see your lines.
The general point to remember is that you don't call any drawing code yourself (except from within drawRect:- you either mark a view as needing display ([myView setNeedsDisplay:YES];, or let the system do that itself.
I know that cocos2d has scheduling callbacks to do nice things but when you need to use one CCAction (like CCMoveTo one) in order to move a sprite from position a to b, you do not have the ability to make small position arrangements to the sprite position for as long as the action is in effect.
The only possible way I found is by making a sub-class of CCMoveTo in order to check for obstacles and therefore provide some kind of movement to the left or right to a sprite that was moving from top to the bottom of the iPhone screen. The problem is that the sub-class does not have access to the parent class' instance variables (like the startPosition_ one) because they have not been declared as properties.
So I used the following snippet to overcome this situation but I wonder if I am doing something wrong...
- (void)myUpdate:(ccTime)time {
if(delegate && method_) {
NSNumber *num = (NSNumber *)[delegate performSelector:method_ withObject:ownTarget];
if(num) {
double xpos = [num doubleValue];
[num release];
CCMoveTo *parent = [super retain];
parent->startPosition_.x += xpos;
[parent release];
}
[super update:time];
}
Is it correct to retain/release the super-class? The "[super update:time];" at the bottom of the code will make the final positioning.
CCMoveTo *parent = [super retain];
Ouch! This statement makes absolutely no sense. It is the same as writing:
[self retain];
As for accessing the super class' instance variables: unless they're declared #private you can access them. I just checked: they're not #private. You should be able to write in your subclass:
startPosition_.x += xpos;
If that doesn't work make sure your class is really a subclass of CCMoveTo, and not some other class.
Finally, I'd like to say that actions are very limited when it comes to implementing gameplay. You're probably much better off to simply animate your game objects by modifying their position property every frame, based on a velocity vector. You have much more freedom over the position and position updates, and none of the side effects of actions such as a one-frame delay every time you run a new action.
-(void) update:(ccTime)delta
{
// modify velocity based on whatever you need, ie gravity, or just heading in one direction
// then update the node's position by adding the current velocity to move it:
self.position = CGPointMake(self.position.x + velocity.x, self.position.y + velocity.y);
}