I'm trying to build something that will only fire a command once per keyboard input (as opposed to every frame like QC does natively). In order to do so, I'm trying to listen in on the keyboard inputs (via Freeboard) and compare the current input versus a previous version.
What seems to be happening is the previous version is getting wiped every time the patch executes, so my conditional to compare strings is failing every time. Here's some code to make it a bit clearer:
- (BOOL)execute:(id <QCPlugInContext>)context atTime:(NSTimeInterval)time withArguments:(NSDictionary *)arguments
{
self.outputPrevious=previousCharacter;
if ([self.inputCharacter caseInsensitiveCompare:previousCharacter]){
self.outputText=#"SAME";
}
else {
self.outputText=#"CHANGE";
}
previousCharacter = [NSString stringWithString:self.inputCharacter];
[previousCharacter retain];
return YES;
}
where self.outputText is the text that tells me the result of the if, self.outputPrevious is telling me what the previous character input was, and self.inputCharacter is the current keyboard input.
previousCharacter is defined in the header and instantiated in -init, so it shouldn't be being reset every time.
I've tried pretty much everything with this, so if you have any ideas or insights, that would be awesome. Thanks!
Figured it out eventually. Full solution can be found here
Related
I'm running an update() method n times per second to "update" the keyboard input from the user so I can read it later in the logic part of the program. So I find two ways of implementing this in the SDL Docs and I'm not sure which one should I use.
1; Loop for all events using SDL_PollEvent searching for key down/up events and saving the key states in a map so I can check for each key state in the logic of the program.
Note: Alternatively, I can also use SDL_PeepEvents instead of SDL_PollEvent to take only the event types that matter; so, it would not "thrown away" the events on the queue.
std::map<int, bool> keyboard; // Saves the state(true=pressed; false=released) of each SDL_Key.
void update()
{
SDL_Event event;
while(SDL_PollEvent(&event))
{
switch(event.type)
{
case SDL_KEYDOWN:
keyboard[event.key.keysym.sym] = false;
break;
case SDL_KEYUP:
keyboard[event.key.keysym.sym] = true;
break;
}
}
}
2; Taking a snapshot from the keyboard each frame so I can read it easily.
Uint8* keyboard;
void update()
{
SDL_PumpEvents();
keyboard = SDL_GetKeyState(NULL);
}
With any of above implementations I can read keyboard just like this:
if (key_map[SDLK_Return]) printf("Return has been pressed.");
Also, is there another way to do so?
I prefer to do a variation of 1, where I fill three arrays, indicating not only the current state, but also which keys just went down and which keys just went up. This allows me to easily check for those events in code (without comparing to the previous snapshot), but, most importantly, it won't miss events that last less than a frame. For example, if your game is running at 10 fps due to a slow machine, the user might press and release an important key between two calls of your update routine, and then your system will never register it. This is extremely frustrating.
SDL also sends key events when the key is held down, which allow you to have multiple key down events for each key up. I find this particularly useful when implementing keyboard scrolling through a list of items, e.g. a keyboard-controlled menu.
You should use solution 2.
Why? As SDL_GetKeyState() docs point out, before using it you are expected to call SDL_PumpEvents() to update the state array.
When you are calling SDL_PollEvent(), it implicitly calls SDL_PumpEvents(). So, it basically updates the array for SDL_GetKeyState() anyway. By parsing these events manually, you just create a second array (well, actually a much slower map) holding the same information which SDL already collected for you.
So, I would dare say that first solution means doing the same thing twice. And if you ever decide to support things such as repeated keystrokes (SDL_EnableKeyRepeat()), you'll be reimplementing even a larger part of SDL.
I realize this question is quite old, but my answer could benefit someone. Personally, I use two arrays with SDL_GetKeyState. I store one array holding the current frame's keyboard state, and one array holding that last frame's keyboard state. (With some memcpy commands, it's really easy to update them.) Along with those two arrays, I have a map that converts strings like "A" to the SDL scancode values, but that is optional.
Then, when you need to check if something is released or pressed, you can combine the two arrays to check. (I made this a function.) For example, if you know that the key is pressed this frame, but wasn't pressed last frame, it was clearly just pressed this frame. if (currentFrame["A"] == true && lastFrame["A"] == false) {/*just pressed*/}
You would then do the opposite for the released. I find that method super easy to implement and use.
When I use NSLog, I get output similar to the following:
2012-01-24 17:05:32:860 App[21856:71939] {logging goes here}
I recognize that '2012-01-24 17:05:32:860' is the date, 'App' is the app name, but I have no clue what '[21856:71939]' means. Can someone fill me in on what that is and where it's generated at?
All I'm trying to do is get logging that lines up nicely so it's easy to read, but the '[21856:71939]' varies in digits enough to mess up any alignment attempts. If I knew how the numbers in '[21856:71939]' were generated, I could add spaces as needed to make it line up correctly, but that's my only idea at this point.
Any help would be much appreciated :)
21856 is the process id. 71939 is the thread id.
You can generate this portion of the log on your own using:
[NSString stringWithFormat:#"[%ld,%lx]",
(long) getpid(),
(long) pthread_mach_thread_np(pthread_self())];
Edit 2014-09-23:
At least on the simulator in iOS 8, the second number is now the pthread_threadid_np of the thread.
__uint64_t threadId;
if (pthread_threadid_np(0, &threadId)) {
threadId = pthread_mach_thread_np(pthread_self());
}
[NSString stringWithFormat:#"[%ld,%llu]", (long) getpid(), threadId]
IIRC, the 21856 is the process PID, and the 71939 is some sort of thread identifier.
It's a thread ID, but I don't actually know how they are generated.
you can grab it yourself using this
pthread_mach_thread_np(pthread_self())
but that doesn't answer how you would set it up with correct lining. On the other note, when you're debugging, go to the last tab (Show the log Navigator), double click on Debug App, it'll show up nicely
I'm writing a simple QR code generator (just for fun and to learn some Obj-C), and I'm working on tracing the outline of connected "modules" (i.e. the black squares that make up a QR code). This is in order to have nicer vector output than simply making a bunch of rects for each module.
Long story short, my outline-tracing code works - BUT ONLY if I make sure to call NSLog in a specific place! If I remove the NSLog-call, the code loops! I'm literally doing nothing but logging. And it doesn't matter what I log; I just have to call NSLog or things break.
The tracing algorithm is simple enough: Go clockwise around the shape of connected modules. When you hit a corner, turn right until you're back to following the outline of the shape. Stop when you reach the starting point again. The shape can have two modules that share a corner-point. The tracing-loop will thus hit that point twice. This is expected, and the code handles it correctly - if I call NSLog.
Otherwise, the code will say that a certain point is a corner the first time it sees it, and not a corner the second time, which causes the tracing to loop around. Detecting if something's a corner-point is not dependent on anything except the x and the y coordinates of the point and an array of module objects - but neither the modules nor the array changes while the tracing is going on, so given the same x,y you should always get the same result. And it does – if I call NSLog.
Without NSLog, the coordinates – e.g. (10,9) – is corner on moment, and a moment later (10,9) is suddenly not a identified as a corner. But with an NSLog-call, (10,9) is correctly seen as a corner-point every time.
Again: I change absolutely nothing; I just log something - anything! And suddenly it works. It's like it's saying that 2 == 2 is true or false, unless I tell it to log 2 and 2, in which case 2 == 2 is always true, as it should be.
Here's the flaky code. It's hard to understand out of context, but there's a lot of context, so I hope this is enough. Everything is integers (no fuzzy floating point values).
do { // start going around the shape
// If this isn't here or simply commented out, the code loops.
NSLog(#"foobar"); // doesn't matter what I log - I just need to log something
// Branch: Is current x,y a corner-point? This should
// always return the same result given the same X and Y
// values, but it only does if NSLog is there!
if( [self cornerAtX:x Y:y] ) {
// add the point to the path
[path addPoint:NSMakePoint(x, y)];
// rotate the direction clockwise, until
// the direction is following the edge of the
// the shape again.
do {
dt = dx;
dx = -dy;
dy = dt;
} while( ![self boundaryFromX:x Y:y inDirectionX:dx Y:dy] );
}
// continue along direction
x += dx;
y += dy;
} while( !(sx == x && sy == y) ); // we're back to the start of the shape, so stop
If anyone can tell me why NSLog can make code work (or rather: Why not using NSLog makes working code break), I'd be happy to hear it! I hope someone can make sense of it.
Make sure cornerAtX:Y: always returns something—i.e., that there's no code path that fails to return a value.
Otherwise, it may very well “return” whatever the last function you called returns, in which case calling NSLog (which doesn't return a value, but may ultimately call a function that does) causes it to “return” something different, which may always be something that's considered true.
The compiler should warn you if you fail to return a value from a function or method that you declared as doing so. You should listen to it. Turn on all the warnings you can get away with and fix all of them.
You should also turn on the static analyzer (also included in that post), as it, too, may tell you about this bug, and if it does, it will tell you step-by-step how it's happening.
There's not much to go on here, but I'd guess that it's either an uninitialized variable or some sort of memory stomping. NSLog probably uses both stack and heap memory, so it could affect those.
Have you tried replacing NSLog with some other meaningless operation? If that will also work then I suppose problem is linked to [self cornerAtX: x Y: y].
Another possibility is that the problem is time-related. NSLog takes time to execute, so if QR code is loaded in another thread you can see this kind of behavior.
I was wondering if there is an effective way to debug problems in xcode while coding in Objective-C. I create webpages constantly and code in jquery and javascript where you can set various alert boxes in different places in your code to determine if your script is properly executing sections. Can you do something like that in xcode to make sure that your script is executing methods properly and creating variables properly?
Thanks
Use the debugger - that's what it is there for! Set breakpoints by clicking in the grey are next to the line of code you want to break on. When this line of code is going to be excuted, the debugger will kick in and highlight the current place in execution. You can hover the cursor over variables in the IDE to examine their values, view the current call-stack (to see here this code has been called from) and get a list of local variables to help track program state. You can modify variable properties here too which often makes debugging simpler.
Execute code line by line by 'Stepping Over' (cmd+shift+o), which executes the current line, 'Stepping Into' (cmd_shift+i) which steps into the current line of code (if it is a function), or 'Stepping Out' to return back up the call stack.
If you want to stick to 'old-school' printf style debugging, go with NSLoging output to console.
NSLog(#"this text appears");
prints the following to the console:
this text appears
To print some basic variable values:
CGFloat pi = 3.14;
NSString *aFloatString = [NSString stringWithFormat:#"%.2f", pi];
NSLog(#"pi is equal to: %#", aFloatString);
Prints:
pi is equa to: 3.14
Standard c formatters can be used in NSLog i.e %d for int, %.2f for a float to 2 decimal places etc. Use %# for NSString*s.
Remember that NSLog will remain in production code unless you #IFDEF it out of release builds (or something similar), so if you don't want a performance hit, or embarrassing console logs to accompany the app you will want to remove them.
I've been known to litter functions that dump the following to console - and it isn't good:
OUTPUT:
Number of vertices is: 1200
<Requested reduction>
Can I kick it?
....
....
YES. I. CAN!
Number of vertices is: 800
Could have done with removing things like that :|
yes, the debugger can do all the things you want to do (just set some breakpoints - right click where you want them - then build&debug)
You can try writing to the console.
NSLog(#"Some status message here");
NSLog(#"The value of myObject is:%#", myObject);
To view the output of your application, while running with Xcode, click Run->Console and you will see all of the output from your application.
first post here so sorry for the length of it. I've been lurking and learning a lot so far but now I have to step in and ask a question. I have read numerous posts here as advised in the FAQs, but I couldn’t find exactly the answer I’m looking for.
Before anything else, let me just say that I'm a total beginner in programming (let alone Objective-C) so please excuse me for any misuse of the terminology. Same goes for any funny english as english not my native language.
I'm building an unit conversion application with a main window containing (among other stuff) two popUpButtons. I'm using indexOfSelectedItem from both popUpButtons in order to calculate a float value (I'm getting the indexes initially in the AwakeFromNib and later in the pop up buttons controller method, when the user change selection).
My problem consists of two parts: first, the code for calculation of that float is pretty massive as I'm comparing every combination of the two indexes of selected items. And second, I would need to have the calculated float value available immediately after launch as the user might want to perform a conversion before using any of the window popUpButtons (otherwise I would put the calculation code in a -(IBAction) method).
So, I'm trying with the following code for calculation of the float value:
#interface MyClass: NSObject
float calculatedFloat;
-(void)setCalculatedFloat:(float)calcFl;
-(float)calculatedFloat;
#implementation MyClass
-(void)setCalculatedFloat:(float)calcFl {
calcFl = 1.0; // I'm simplifying, this is where I'd like to perform calculation
}
-(float)calculatedFloat {
return calculatedFloat;
}
Now, for the first part of my problem, when I use the calculatedFloat in another method, say:
-(void)printIt {
NSLog(#"Calculated float equals: %.2f", calulatedFloat);
}
all I receive in Debugger is 0.00.
First question would be: if this is not working, how do I properly access this value from within another method?
For the second part of the problem, I'm using -(void)AwakeFromNib; to set up popUpButtons etc. right after the launch but I really wouldn't like to put all of the float calculation code in it only to repeat it somewhere else later.
So the second question would be: is this even possible what I'm trying to achieve? Further more, do I need to move this calculation code to another class? If so, how can I make that other class aware of the indexOfSelectedItem from a popUpButton?
Sorry for the lengthy post and possibly confusing and silly questions. I hope you didn't have to cringe your teeth too much while reading! :)
Thanks!
-(void)setCalculatedFloat:(float)calcFl {
calcFl = 1.0; // I'm simplifying, this is where I'd like to perform calculation
}
This doesn't show up when you print it later because you assigned to the variable holding the new value, not the variable for the value of the property. You need to assign to your calulatedFloat instance variable.
(You typo'ed that variable name, BTW.)
You should move the calculating into another method, and send yourself that message from awakeFromNib and from anywhere that needs to cause recalculation. That method should call setCalculatedFloat: with the calculated value—i.e., setCalculatedFloat: should be just a simple setter. Once you make that change, you could replace your custom accessors with a #synthesize statement and let the compiler write the accessors for you.
My problem consists of two parts: first, the code for calculation of that float is pretty massive as I'm comparing every combination of the two indexes of selected items.
You might see whether you can create custom objects to set as the menu items' representedObject properties, in order to cut out this massive comparison tree. It's hard to be more specific about this without knowing what your comparison tree does.