我正在为我的应用寻找在用户使用Command-Shift-3 或Command-Shift-4 截屏时接收通知的方法。
这方面的一个例子是像 Droplr 和 Cloud App 这样的应用程序，它们会自动上传截取的屏幕截图。
我一直在四处寻找，发现它可能与达尔文通知有关，但我不确定从哪里开始。
【问题讨论】：
标签： objective-c cocoa macos notifications
这在较早的 cmets 之一中已提及，但您可以使用 NSMetadataQuery 搜索 kMDItemIsScreenCapture = 1 所在的文件。这是添加到屏幕截图文件中的特殊属性。
我刚刚制作了一个小演示来展示如何做到这一点并将其发布在 github 上：
https://github.com/davedelong/Demos/blob/master/ScreenShot%20Detector
【讨论】：
这就是我的做法，有点复杂，但我会尝试一步一步地告诉你：
在我们开始之前，在您的头文件中声明以下变量和方法：
BOOL shouldObserveDesktop;
NSDictionary *knownScreenshotsOnDesktop;
NSString *screenshotLocation;
NSString *screenshotFilenameSuffix;
- (void)startObservingDesktop;
- (void)stopObservingDesktop;
- (NSDictionary *)screenshotsOnDesktop;
- (NSDictionary *)screenshotsAtPath:(NSString *)dirpath modifiedAfterDate:(NSDate *)lmod;
- (void)checkForScreenshotsAtPath:(NSString *)dirpath;
- (NSDictionary *)findUnprocessedScreenshotsOnDesktop;
现在在您的实现文件中，首先添加以下代码：
- (void)applicationDidFinishLaunching:(NSNotification *)aNotification {
screenshotLocation = [[NSString stringWithString:@"~/Desktop"] retain];
screenshotFilenameSuffix = [[NSString stringWithString:@".png"] retain];
knownScreenshotsOnDesktop = [[self screenshotsOnDesktop] retain];
[self startObservingDesktop];
}
这将为调用所有方法时设置变量。下一个补充：
- (void)onDirectoryNotification:(NSNotification *)n {
id obj = [n object];
if (obj && [obj isKindOfClass:[NSString class]]) {
[self checkForScreenshotsAtPath:screenshotLocation];
}
}
- (void)startObservingDesktop {
if (shouldObserveDesktop)
return;
NSDistributedNotificationCenter *dnc = [NSDistributedNotificationCenter defaultCenter];
[dnc addObserver:self selector:@selector(onDirectoryNotification:) name:@"com.apple.carbon.core.DirectoryNotification" object:nil suspensionBehavior:NSNotificationSuspensionBehaviorDeliverImmediately];
shouldObserveDesktop = YES;
}
- (void)stopObservingDesktop {
if (!shouldObserveDesktop)
return;
NSDistributedNotificationCenter *dnc = [NSDistributedNotificationCenter defaultCenter];
[dnc removeObserver:self name:@"com.apple.carbon.core.DirectoryNotification" object:nil];
shouldObserveDesktop = NO;
}
这里我们观察在截屏时将调用的通知，并将调用的方法传递给它（在本例中为onDirectoryNotification:）。还有停止观察桌面/通知的方法。通知调用checkForScreenshotsAtPath:，它将检查桌面上的屏幕截图。以下是该方法及其调用的其他方法的代码：
-(void)checkForScreenshotsAtPath:(NSString *)dirpath {
NSDictionary *files;
NSArray *paths;
// find new screenshots
if (!(files = [self findUnprocessedScreenshotsOnDesktop]))
return;
// sort on key (path)
paths = [files keysSortedByValueUsingComparator:^(id a, id b) { return [b compare:a]; }];
// process each file
for (NSString *path in paths) {
// Process the file at the path
}
}
-(NSDictionary *)findUnprocessedScreenshotsOnDesktop {
NSDictionary *currentFiles;
NSMutableDictionary *files;
NSMutableSet *newFilenames;
currentFiles = [self screenshotsOnDesktop];
files = nil;
if ([currentFiles count]) {
newFilenames = [NSMutableSet setWithArray:[currentFiles allKeys]];
// filter: remove allready processed screenshots
[newFilenames minusSet:[NSSet setWithArray:[knownScreenshotsOnDesktop allKeys]]];
if ([newFilenames count]) {
files = [NSMutableDictionary dictionaryWithCapacity:1];
for (NSString *path in newFilenames) {
[files setObject:[currentFiles objectForKey:path] forKey:path];
}
}
}
knownScreenshotsOnDesktop = currentFiles;
return files;
}
-(NSDictionary *)screenshotsOnDesktop {
NSDate *lmod = [NSDate dateWithTimeIntervalSinceNow:-5]; // max 5 sec old
return [self screenshotsAtPath:screenshotLocation modifiedAfterDate:lmod];
}
它们是通知依次调用的前 3 个方法，下面的代码是最后一个方法 screenshotsAtPath:modifiedAfterDate:，我会警告你，它非常长，因为它必须确认文件绝对是屏幕截图：
-(NSDictionary *)screenshotsAtPath:(NSString *)dirpath modifiedAfterDate:(NSDate *)lmod {
NSFileManager *fm = [NSFileManager defaultManager];
NSArray *direntries;
NSMutableDictionary *files = [NSMutableDictionary dictionary];
NSString *path;
NSDate *mod;
NSError *error;
NSDictionary *attrs;
dirpath = [dirpath stringByExpandingTildeInPath];
direntries = [fm contentsOfDirectoryAtPath:dirpath error:&error];
if (!direntries) {
return nil;
}
for (NSString *fn in direntries) {
// always skip dotfiles
if ([fn hasPrefix:@"."]) {
//[log debug:@"%s skipping: filename begins with a dot", _cmd];
continue;
}
// skip any file not ending in screenshotFilenameSuffix (".png" by default)
if (([fn length] < 10) ||
// ".png" suffix is expected
(![fn compare:screenshotFilenameSuffix options:NSCaseInsensitiveSearch range:NSMakeRange([fn length]-5, 4)] != NSOrderedSame)
)
{
continue;
}
// build path
path = [dirpath stringByAppendingPathComponent:fn];
// Skip any file which name does not contain a space.
// You want to avoid matching the filename against
// all possible screenshot file name schemas (must be hundreds), we make the
// assumption that all language formats have this in common: it contains at least one space.
if ([fn rangeOfString:@" "].location == NSNotFound) {
continue;
}
// query file attributes (rich stat)
attrs = [fm attributesOfItemAtPath:path error:&error];
if (!attrs) {
continue;
}
// must be a regular file
if ([attrs objectForKey:NSFileType] != NSFileTypeRegular) {
continue;
}
// check last modified date
mod = [attrs objectForKey:NSFileModificationDate];
if (lmod && (!mod || [mod compare:lmod] == NSOrderedAscending)) {
// file is too old
continue;
}
// find key for NSFileExtendedAttributes
NSString *xattrsKey = nil;
for (NSString *k in [attrs keyEnumerator]) {
if ([k isEqualToString:@"NSFileExtendedAttributes"]) {
xattrsKey = k;
break;
}
}
if (!xattrsKey) {
// no xattrs
continue;
}
NSDictionary *xattrs = [attrs objectForKey:xattrsKey];
if (!xattrs || ![xattrs objectForKey:@"com.apple.metadata:kMDItemIsScreenCapture"]) {
continue;
}
// ok, let's use this file
[files setObject:mod forKey:path];
}
return files;
}
嗯，你有它。这就是我能够检测到用户何时截屏的方式，它可能有一些错误，但目前似乎工作正常。如果您想将所有代码合二为一，请查看 pastebin.com 上的链接：
【讨论】：
com.apple.screencapture 默认值不存在。
NSDictionary *xattrs = [attrs objectForKey:@"NSFileExtendedAttributes"];
您必须注册一个对象才能在用户截屏时接收系统通知
所以：
[[NSNotificationCenter defaultCenter] addObserver: theObjectToRecieveTheNotification selector:@selector(theMethodToPerformWhenNotificationIsRecieved) name:@"theNameOftheScreenCapturedNotification" object: optionallyAnObjectOrArgumentThatIsPassedToTheMethodToBecalled];
不确定通知名称是什么，但它可能在外面。
不要忘记在 dealloc 中注销自己：
[[NSNotificationCenter defaultCenter] removeObserver:self];
【讨论】：