I'm trying to code a little command line tool using Xcode (under MacOS 10.10) that watches a specific folder and informs me about changes to files in that folder.
I'm following the guide given in https://developer.apple.com/library/mac/documentation/Darwin/Conceptual/FSEvents_ProgGuide/UsingtheFSEventsFramework/UsingtheFSEventsFramework.html
Here is my current code:
#import <Foundation/Foundation.h>
#include <CoreServices/CoreServices.h>
void mycallback(
ConstFSEventStreamRef streamRef,
void *clientCallBackInfo,
size_t numEvents,
void *eventPaths,
const FSEventStreamEventFlags eventFlags[],
const FSEventStreamEventId eventIds[])
{
int i;
char **paths = eventPaths;
printf("Callback called\n");
for (i=0; i<numEvents; i++) {
int count;
/* flags are unsigned long, IDs are uint64_t */
printf("Change %llu in %s, flags %lu\n", eventIds[i], paths[i], eventFlags[i]);
}
}
int main(int argc, const char * argv[]) {
// #autoreleasepool {
// insert code here...
NSLog(#"Starting to watch ");
/* Define variables and create a CFArray object containing
CFString objects containing paths to watch.
*/
CFStringRef mypath = CFSTR("/Users/testuser/");
CFArrayRef pathsToWatch = CFArrayCreate(NULL, (const void **)&mypath, 1, NULL);
void *callbackInfo = NULL; // could put stream-specific data here.
FSEventStreamRef stream;
CFAbsoluteTime latency = 3.0; /* Latency in seconds */
/* Create the stream, passing in a callback */
stream = FSEventStreamCreate(NULL,
&mycallback,
callbackInfo,
pathsToWatch,
kFSEventStreamEventIdSinceNow, /* Or a previous event ID */
latency,
kFSEventStreamCreateFlagNone /* Flags explained in reference */
);
/* Create the stream before calling this. */
FSEventStreamScheduleWithRunLoop(stream, CFRunLoopGetCurrent(),kCFRunLoopDefaultMode);
FSEventStreamStart(stream);
CFRunLoopRun();
return 0;
}
The code compiles and can be started. However, no events are being fired. I'm pretty new to Xcode and also never ever used a callback function before. So I guess that this is a pretty dumb mistake that I made.
I'd appreciate any hints that may help.
Thanks in advance
Norbert
Update: The code was updated with a working solution from the answer.
According to the documentation, after starting event stream to send events, you should call CFRunLoopRun.
Try to change your while() loop to:
CFRunLoopRun();
Update. My output:
$ ./fsevent
2015-05-17 13:51:29.718 fsevent[898:23601] Starting to watch
Callback called
Change 1165579 in /Users/baf/src/tests/, flags 66560
Callback called
Change 1165594 in /Users/baf/src/tests/, flags 66048
It appears you have FSEventStreamRef stream; commented out. In order to start watching events you'll want to uncomment that line. It also looks like your callback print statement is also commented out, although that appears to be just for debugging perhaps.
Related
I get strange code errors when I rename the following command line program from main.m to main.mm. Works just fine as main.m. Anyone know why?
https://stackoverflow.com/a/36469891/105539
SOURCE
#import <Foundation/Foundation.h>
void detectNewFile (
ConstFSEventStreamRef streamRef,
void *clientCallBackInfo,
size_t numEvents,
void *eventPaths,
const FSEventStreamEventFlags eventFlags[],
const FSEventStreamEventId eventIds[])
{
int i;
char **paths = eventPaths;
printf("GOT AN EVENT!!!!\n");
for (i=0; i<numEvents; i++) {
printf("Change %llu in %s, flags %u\n", eventIds[i], paths[i], (unsigned int)eventFlags[i]);
}
}
int main(int argc, const char * argv[]) {
#autoreleasepool {
short nPathCount = 2;
CFStringRef mypath[nPathCount];
mypath[0] = CFSTR("/Users/mike/Documents");
mypath[1] = CFSTR("/Users/mike/Downloads");
CFArrayRef pathsToWatch = CFArrayCreate(NULL, (const void **)&mypath, nPathCount, NULL);
void *callbackInfo = NULL;
CFAbsoluteTime latency = 1.0; // seconds
FSEventStreamRef hStream = FSEventStreamCreate(NULL,
&detectNewFile,
callbackInfo,
pathsToWatch,
kFSEventStreamEventIdSinceNow,
latency,
kFSEventStreamCreateFlagFileEvents
);
FSEventStreamScheduleWithRunLoop(hStream, CFRunLoopGetCurrent(), kCFRunLoopDefaultMode);
FSEventStreamStart(hStream);
printf("Waiting on new file creations...\n");
CFRunLoopRun(); // runs in an endless loop, only letting the callback function run
} // end autorelease pool
return 0;
}
ERRORS
FOR:
char **paths = eventPaths;
Cannot initialize a variable of type 'char **' with an lvalue of type 'void *'
FOR:
FSEventStreamRef hStream = FSEventStreamCreate(NULL,
&detectNewFile,
callbackInfo,
pathsToWatch,
kFSEventStreamEventIdSinceNow,
latency,
kFSEventStreamCreateFlagFileEvents
);
No matching function for call to 'FSEventStreamCreate'
Thanks to #johnelemans, I found the problems. In C, it's legal to have automatic casting from void * to char **, but not in C++, which is what the .mm file would switch this into. The fix is to use casting:
char **paths = (char **)eventPaths;
Then, on the FSEventStreamCreate, it didn't like the void * instead of this:
FSEventStreamContext *callbackInfo = NULL;
...and didn't like the CFAbsoluteTime instead of:
CFTimeInterval latency = 1.0; // seconds
Then, you need to add CoreServices.framework library to the build steps.
I made those changes and it compiles now.
I'm working on a desktop application that watch folders using the fileevent api, so basically this is my code :
#import "PNAppDelegate.h"
void callback(
ConstFSEventStreamRef streamRef,
void *clientCallBackInfo,
size_t numEvents,
void *eventPaths,
const FSEventStreamEventFlags eventFlags[],
const FSEventStreamEventId eventIds[])
{
[(__bridge PNAppDelegate *)clientCallBackInfo reloadStatus];
};
#implementation PNAppDelegate
#synthesize window = _window;
- (void)applicationDidFinishLaunching:(NSNotification *)aNotification
{
NSArray *pathsToWatch = [NSArray arrayWithObject: #"/Users/romainpouclet/Projects/foo"];
void *appPointer = (__bridge void *)self;
FSEventStreamContext context = {0, appPointer, NULL, NULL, NULL};
FSEventStreamRef stream;
CFAbsoluteTime latency = 3.0;
stream = FSEventStreamCreate(NULL,
&callback,
&context,
(__bridge CFArrayRef) pathsToWatch,
kFSEventStreamEventIdSinceNow,
latency,
kFSEventStreamCreateFlagNone);
NSLog(#"Schedule with run loop");
FSEventStreamScheduleWithRunLoop(stream, CFRunLoopGetMain(), kCFRunLoopDefaultMode);
FSEventStreamStart(stream);
[self reloadStatus];
}
-(void)reloadStatus
{
}
#end
No problem, it works pretty well for a POC as simple as this one, BUT it feels kinda ugly (and it probably is, I'm not really used to mix Objective-C and C). So here are my questions :
where should I declare my callback? It feels weird having it at the top of my file, just because it worked there.
is it possible to have some kind of #selector-based approach instead of callbacks? (I find them reassuring :D)
Thanks for your time !
Why not put the callback declaration in either PNAppDelegate.h, or its own header file (if you don't want to spread it around your app). That way you can just include the header file and put the function definition anywhere you want. Doing so is standard C functionality.
// Header file callback.h
void callback(
ConstFSEventStreamRef streamRef,
void *clientCallBackInfo,
size_t numEvents,
void *eventPaths,
const FSEventStreamEventFlags eventFlags[],
const FSEventStreamEventId eventIds[]);
// PNAppDelegate.m
#import "PNAppDelegate.h"
#import "callback.h"
#implementation PNAppDelegate
...
#end
void callback(
ConstFSEventStreamRef streamRef,
void *clientCallBackInfo,
size_t numEvents,
void *eventPaths,
const FSEventStreamEventFlags eventFlags[],
const FSEventStreamEventId eventIds[])
{
[(__bridge PNAppDelegate *)clientCallBackInfo reloadStatus];
};
You are correct, that code IS ugly. However, bridging C and Obj-C is no small task, so you really only have a few options:
Create an Objective-C wrapper around the C-based API. This would be my recommended approach, especially if the API is not too complex. It gives you the advantage of using either delegates or blocks, instead of functions.
Use blocks for callbacks, by getting their internal function pointer:
// internal structure of a block
struct blockPtr {
void *__isa;
int __flags;
int __reserved;
void *__FuncPtr;
void *__descriptor;
};
int main()
{
#autoreleasepool {
__block int b = 0;
void (^blockReference)(void *) = ^(void *arg) {
NSLog(#"<%s>: %i", arg, b++);
};
void *blockFunc = ((__bridge struct blockPtr *) blockReference)->__FuncPtr;
void (*castedFunction)(void *, void *) = blockFunc;
// the first argument to any block funciton is the block
// reference itself, similar to how the first argument to
// any objc function is 'self', however, in most cases you
// don't need the block reference (unless reading __block variables), it's just difficult to
// get that first argument from inside the block
castedFunction((__bridge void *) blockReference, "one");
castedFunction((__bridge void *) blockReference, "two");
}
}
I really don't think this is practical in most situations, but if you can find a way to make it work, more power to you.
Stick with how you are currently doing it. It sucks, but that is how C works.
And note that I can not pass in a ViewController pointer due to this function being passed into another function.
static int callback(void *NotUsed, int argc, char **argv, char **azColName)
{
NSString *str = #"";
int i;
for(i=0; i<argc; i++)
{
printf("%s = %s\n", azColName[i], argv[i] ? argv[i] : "NULL");
str = [NSString stringWithFormat:#"%#\n%s = %s\n", str, azColName[i], argv[i] ? argv[i] : "NULL"];
}
printf("\n");
//tvDisplay is a UITextView
[tvDisplay setText:str]; // <---- ??? how to get to an iVar
return 0;
}
the call:
rc = sqlite3_exec(db, pSQL[i], callback, 0, &zErrMsg);
Callback functions typically have an argument that allows you to pass along arbitrary data (it's usually a void * called context or something similar). You can pass in the object that you need to access when you set up the callback function, and then retrieve it within the callback function:
static void myCallback(int someResult, void *context) {
SomeClass *someObject = (SomeClass *)context;
[someObject doStuff];
}
In your particular case, the place for the "arbitrary data that you want to access in the callback function" is the void * argument right after the callback function itself that you have presently set to 0:
int sqlite3_exec(
sqlite3*, /* An open database */
const char *sql, /* SQL to be evaluated */
int (*callback)(void*,int,char**,char**), /* Callback function */
void *, /* 1st argument to callback */
char **errmsg /* Error msg written here */
);
Keep in mind that you're responsible for ensuring that any data you stick in there remains valid while the callback has not yet returned, and, if necessary, free it in the callback.
Apologies if this is a stupid/easy question, but still getting used to everything in Mac land.
Dave was kind enough to answer a question for me here:
Modify NSEvent to send a different key than the one that was pressed
which resulted in the following code, which works great:
#import <Cocoa/Cocoa.h>
CGEventRef myCGEventCallback(CGEventTapProxy proxy, CGEventType type, CGEventRef event, void *refcon) {
//0x0b is the virtual keycode for "b"
//0x09 is the virtual keycode for "v"
if (CGEventGetIntegerValueField(event, kCGKeyboardEventKeycode) == 0x0B) {
CGEventSetIntegerValueField(event, kCGKeyboardEventKeycode, 0x09);
}
return event;
}
int main(int argc, char *argv[]) {
//return NSApplicationMain(argc, (const char **)argv);
NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];
CFRunLoopSourceRef runLoopSource;
CFMachPortRef eventTap = CGEventTapCreate(kCGHIDEventTap, kCGHeadInsertEventTap, kCGEventTapOptionDefault, kCGEventMaskForAllEvents, myCGEventCallback, NULL);
if (!eventTap) {
NSLog(#"Couldn't create event tap!");
exit(1);
}
runLoopSource = CFMachPortCreateRunLoopSource(kCFAllocatorDefault, eventTap, 0);
CFRunLoopAddSource(CFRunLoopGetCurrent(), runLoopSource, kCFRunLoopCommonModes);
CGEventTapEnable(eventTap, true);
CFRunLoopRun();
CFRelease(eventTap);
CFRelease(runLoopSource);
[pool release];
exit(0);
}
Thanks to some helpful error messages (can't have two "main" methods) I figured out that I had to put this code in the main.m file (right?). That means I'm overwriting the default method:
int main(int argc, char *argv[]) {
return NSApplicationMain(argc, (const char **)argv);
}
Which means none of my other Objective-C based code is firing. But if I uncomment that bit (or make any other attempt to call NSApplicationMain) then the main.m run loop is what doesn't run.
I imagine this is fairly simple for a seasoned Mac guy, but I'm having a hard time wrapping my head around it. Thanks.
I don't see any reason why the same idea won't work elsewhere in your code. Can you put it in the -applicationDidFinishLaunching: method of your app delegate? If you do, you will not need the CFRunLoop() call, since the run loop will already be running. Nor will you need the autorelease pool bit.
there is an app called FreeStyler, that you can control using midi commands. In my mac app I want to send midi signals.
Can someone show an example of this?
Elijah
This is what it took to send a note to my blofeld synth. I hope it helps. You can use MIDIObjectGetProperties to find the uniqueIDs for all the midi devices connected to your mac.
#import <Foundation/Foundation.h>
#import <CoreMIDI/CoreMIDI.h>
MIDIEndpointRef getEndpointWithUniqueID(MIDIUniqueID id){
MIDIObjectRef endPoint;
MIDIObjectType foundObj;
MIDIObjectFindByUniqueID(id, &endPoint, &foundObj);
return (MIDIEndpointRef) endPoint;
}
MIDIClientRef getMidiClient(){
MIDIClientRef midiClient;
NSString *outPortName =#"blofeldOut";
MIDIClientCreate((CFStringRef)outPortName, NULL, NULL, &midiClient);
return midiClient;
}
MIDIPortRef getOutPutPort(){
MIDIPortRef outPort;
NSString *outPortName =#"blofeldOut";
MIDIOutputPortCreate(getMidiClient(), (CFStringRef)outPortName, &outPort);
return outPort;
}
MIDIPacketList getMidiPacketList(){
MIDIPacketList packetList;
packetList.numPackets = 1;
MIDIPacket* firstPacket = &packetList.packet[0];
firstPacket->timeStamp = 0; // send immediately
firstPacket->length = 3;
firstPacket->data[0] = 0x90;
firstPacket->data[1] = 60;
firstPacket->data[2] = 64;
// TODO: add end note sequence
return packetList;
}
void play_note(void) {
NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];
MIDIPacketList packetList=getMidiPacketList();
MIDIUniqueID blofeldEndpointID = -934632258;
MIDIEndpointRef blofeldEndpoint = getEndpointWithUniqueID(blofeldEndpointID);
MIDISend(getOutPutPort(), blofeldEndpoint, &packetList);
MIDIEndpointDispose(blofeldEndpoint);
[pool drain];
}
int main (int argc, const char * argv[]) {
play_note();
return 0;
}
Your application will need to use the CoreMIDI framework to send or receive MIDI, which I can tell you from experience is not a lot of fun to work with directly. You might want to try the vvopensource framework, which is a MIDI framework designed for cocoa.