How do I stop a block enumeration?
myArray.enumerateObjectsUsingBlock( { object, index, stop in
//how do I stop the enumeration in here??
})
I know in obj-c you do this:
[myArray enumerateObjectsUsingBlock:^(id *myObject, NSUInteger idx, BOOL *stop) {
*stop = YES;
}];
In Swift 1:
stop.withUnsafePointer { p in p.memory = true }
In Swift 2:
stop.memory = true
In Swift 3 - 4:
stop.pointee = true
This has unfortunately changed every major version of Swift. Here's a breakdown:
Swift 1
stop.withUnsafePointer { p in p.memory = true }
Swift 2
stop.memory = true
Swift 3
stop.pointee = true
since XCode6 Beta4, the following way can be used instead:
let array: NSArray = // the array with some elements...
array.enumerateObjectsUsingBlock( { (object: AnyObject!, idx: Int, stop: UnsafePointer<ObjCBool>) -> Void in
// do something with the current element...
var shouldStop: ObjCBool = // true or false ...
stop.initialize(shouldStop)
})
The accepted answer is correct but will work for NSArrays only. Not for the Swift datatype Array. If you like you can recreate it with an extension.
extension Array{
func enumerateObjectsUsingBlock(enumerator:(obj:Any, idx:Int, inout stop:Bool)->Void){
for (i,v) in enumerate(self){
var stop:Bool = false
enumerator(obj: v, idx: i, stop: &stop)
if stop{
break
}
}
}
}
call it like
[1,2,3,4,5].enumerateObjectsUsingBlock({
obj, idx, stop in
let x = (obj as Int) * (obj as Int)
println("\(x)")
if obj as Int == 3{
stop = true
}
})
or for function with a block as the last parameter you can do
[1,2,3,4,5].enumerateObjectsUsingBlock(){
obj, idx, stop in
let x = (obj as Int) * (obj as Int)
println("\(x)")
if obj as Int == 3{
stop = true
}
}
Just stop = true
Since stop is declared as inout, swift will take care of mapping the indirection for you.
Related
I've been having issues converting an Objective-C snippet to Swift that uses NSData and CoreBluetooth. I have looked at this question and a couple others dealing with NSData in Swift but haven't had any success.
Objective-C Snippet:
- (CGFloat) minTemperature
{
CGFloat result = NAN;
int16_t value = 0;
// characteristic is a CBCharacteristic
if (characteristic) {
[[characteristic value] getBytes:&value length:sizeof (value)];
result = (CGFloat)value / 10.0f;
}
return result;
}
What I have so far in Swift (not working):
func minTemperature() -> CGFloat {
let bytes = [UInt8](characteristic?.value)
let pointer = UnsafePointer<UInt8>(bytes)
let fPointer = pointer.withMemoryRebound(to: Int16.self, capacity: 2) { return $0 }
value = Int16(fPointer.pointee)
result = CGFloat(value / 10) // not correct value
return result
}
Does the logic look wrong here? Thanks!
One error is in
let fPointer = pointer.withMemoryRebound(to: Int16.self, capacity: 2) { return $0 }
because the rebound pointer $0 is only valid inside the closure and must
not be passed to the outside. Also the capacity should be 1 for a
single Int16 value. Another problem is the integer division in
result = CGFloat(value / 10)
which truncates the result (as already observed by the4kman).
Creating an [UInt8] array from the data is not necessary, the
withUnsafeBytes() method of Data can be used instead.
Finally you could return nil (instead of "not a number") if no
characteristic value is given:
func minTemperature() -> CGFloat? {
guard let value = characteristic?.value else {
return nil
}
let i16val = value.withUnsafeBytes { (ptr: UnsafePointer<Int16>) in
ptr.pointee
}
return CGFloat(i16val) / 10.0
}
You should make the return value optional and check if characteristic is nil in the beginning with a guard. You should also explicitly convert the value to CGFloat, then divide it by 10.
func minTemperature() -> CGFloat? {
guard characteristic != nil else {
return nil
}
let bytes = [UInt8](characteristic!.value)
let pointer = UnsafePointer<UInt8>(bytes)
let fPointer = pointer.withMemoryRebound(to: Int16.self, capacity: 2) { return $0 }
let value = Int16(fPointer.pointee)
result = CGFloat(value) / 10
return result
}
Objective C Code:
- (instancetype)initWithInts:(int32_t)int1, ... {
va_list args;
va_start(args, int1);
unsigned int length = 0;
for (int32_t i = int1; i != -1; i = va_arg(args, int)) {
length ++;
}
va_end(args);
...
...
return self;
}
This code is used to count the numbers of method's parameters.
Swift Code:
convenience init(ints: Int32, _ args: CVarArgType...) {
var length: UInt = 0
self.init(length: args.count)
withVaList(args, { _ in
// How to increase length' value in loop?
})
}
What's the best practise to use withVaList to loop through the argument list with a CVaListPointer? Help is very appreciated.
How about just
convenience init(args: Int...) {
return args.count
}
convenience required init(args: Int32...) {
}
If you define your func parameter following by three dots ..., you will notice args is actually a [Int32] type.
So just do casting likes Array, i.e. args.count, for i in args.
-(CGPoint*)func
{
CGPoint* result = calloc(2, sizeof(CGPoint));
result[0] = ..;
result[1] = ..;
return result;
}
how cast this array to swift [CGPoint] ?
You can use UnsafeBufferPointer to cast it as follows
let pointer: UnsafeMutablePointer<CGPoint> = yourInstance.func()
let swiftArray = Array(UnsafeBufferPointer(start: pointer, count: 2))
free(pointer)
EDIT
If you really need to use C arrays, you may want to rewrite the func method to something like:
- (CGPoint*)pointArray:(NSInteger *)length
{
int arrSize = 2;
CGPoint* result = calloc(arrSize, sizeof(CGPoint));
result[0] = ...
result[1] = ...
*length = arrSize;
return result;
}
Then on the Swift side:
var arrayLength: Int = 0
let pointer: UnsafeMutablePointer<CGPoint> = yourInstance.pointArray(&arrayLength)
let swiftArray = Array(UnsafeBufferPointer(start: pointer, count: arrayLength))
free(pointer)
How can I use the Objective-C code below in Swift, I tried but something is wrong.
Objective-C:
NSUInteger index = [theArray indexOfObjectPassingTest:
^BOOL(NSDictionary *dict, NSUInteger idx, BOOL *stop)
{
return [[dict objectForKey:#"name"] isEqual:theValue];
}
];
Swift (Doesn't work):
let index = theArray.indexOfObjectPassingTest { (var dict: NSDictionary, var ind: Int, var bool: Bool) -> Bool in
return dict.objectForKey("name")?.isEqual("theValue")
}
I played with it and got this to work:
let theArray: NSArray = [["name": "theName"], ["name": "theStreet"], ["name": "theValue"]]
let index = theArray.indexOfObjectPassingTest { (dict, ind, bool) in return dict["name"] as? String == "theValue" }
if index == NSNotFound {
print("not found")
} else {
print(index) // prints "2"
}
This can be further reduced. As #newacct mentioned in the comment, the return can be dropped since the closure is only a single line. Also, _ can be used in place of the parameters that aren't being used:
let index = theArray.indexOfObjectPassingTest { (dict, _, _) in dict["name"] as? String == "theValue" }
You can get rid of the parameter list in the closure entirely and use the default $0 value. Note in that case, the three parameters are combined as a tuple, so the first value of the tuple dict is referenced as $0.0:
let index = theArray.indexOfObjectPassingTest { $0.0["name"] as? String == "theValue" }
Swift 3:
Consider this method:
public func index(where predicate: (Element) throws -> Bool) rethrows -> Int?
The following gives you an example how to use it:
let dict1 = ["name": "Foo"]
let dict2 = ["name": "Doh"]
let array = [dict1, dict2]
let index = array.index { (dictionary) -> Bool in
return dictionary["name"] == "Doh"
}
This returns the value 1.
Hope that helps
Guess you need this:
var index: UInt = theArray.indexOfObjectPassingTest({(dict: [NSObject: AnyObject], idx: UInt, stop: Bool) -> BOOL in return dict.objectForKey("name").isEqual(theValue)
})
I ended up using this for a Swift5 project:
let index = self.info.indexOfObject(passingTest: { (obj:Any, ind:Int, stop:UnsafeMutablePointer<ObjCBool>) -> Bool in
if let details = obj as? NSDictionary, let id = details["id"] as? Int
{
if (orderId == id)
{
stop.pointee = true
return true
}
}
return false;
})
Where orderId is id value of the object I wanted to find.
I was trying to access temp directory in Swift. In Objective-C, I could use the following code to do so:
- (NSString *)tempDirectory {
NSString *tempDirectoryTemplate =
[NSTemporaryDirectory() stringByAppendingPathComponent:#"XXXXX"];
const char *tempDirectoryTemplateCString = [tempDirectoryTemplate fileSystemRepresentation];
char *tempDirectoryNameCString = (char *)malloc(strlen(tempDirectoryTemplateCString) + 1);
strcpy(tempDirectoryNameCString, tempDirectoryTemplateCString);
char *result = mkdtemp(tempDirectoryNameCString);
if (!result) {
return nil;
}
NSString *tempDirectoryPath = [[NSFileManager defaultManager] stringWithFileSystemRepresentation:tempDirectoryNameCString length:strlen(result)];
free(tempDirectoryNameCString);
return tempDirectoryPath;
}
However, I'm a bit confuse about the type conversion and casting from Objective-C to Swift, such as const char * or CMutablePointer<CChar>. Is there any documents that I should look into?
Thanks.
How about something like :
public extension FileManager {
func createTempDirectory() throws -> String {
let tempDirectory = (NSTemporaryDirectory() as NSString).appendingPathComponent(UUID().uuidString)
try FileManager.default.createDirectory(atPath: tempDirectory,
withIntermediateDirectories: true,
attributes: nil)
return tempDirectory
}
}
It doesn't answer your question about char* but it's cleaner...
NSFileManager reference here.
Also check out this SO question regarding unique names.
According to Apple, use of NSTemporaryDirectory is discouraged:
See the FileManager method url(for:in:appropriateFor:create:) for the
preferred means of finding the correct temporary directory. For more
information about temporary files, see File System Programming Guide.
So instead, you should use FileManager.default.temporaryDirectory
or if you want an unique path:
let extractionPath = FileManager.default.temporaryDirectory.appendingPathComponent(UUID().uuidString, isDirectory: true)
Swift 2.1 version:
func createTempDirectory() -> String? {
let tempDirURL = NSURL(fileURLWithPath: NSTemporaryDirectory()).URLByAppendingPathComponent("XXXXXX")
do {
try NSFileManager.defaultManager().createDirectoryAtURL(tempDirURL, withIntermediateDirectories: true, attributes: nil)
} catch {
return nil
}
return tempDirURL.absoluteString
}
Swift 3 and up
I think a good way to do this in swift is with an extension on FileManager. This should create a unique temporary folder and return the URL to you.
extension FileManager{
func createTemporaryDirectory() throws -> URL {
let url = URL(fileURLWithPath: NSTemporaryDirectory()).appendingPathComponent(UUID().uuidString)
try createDirectory(at: url, withIntermediateDirectories: true, attributes: nil)
return url
}
}
Swift 3 version
func createTempDirectory() -> String? {
guard let tempDirURL = NSURL(fileURLWithPath: NSTemporaryDirectory()).appendingPathComponent("myTempFile.xxx") else {
return nil
}
do {
try FileManager.default.createDirectory(at: tempDirURL, withIntermediateDirectories: true, attributes: nil)
} catch {
return nil
}
return tempDirURL.absoluteString
}
A direct translation of your Objective-C code to Swift would be:
func tempDirectory()->String! {
let tempDirectoryTemplate = NSTemporaryDirectory() + "XXXXX"
var tempDirectoryTemplateCString = tempDirectoryTemplate.fileSystemRepresentation().copy()
let result : CString = reinterpretCast(mkdtemp(&tempDirectoryTemplateCString))
if !result {
return nil
}
let fm = NSFileManager.defaultManager()
let tempDirectoryPath = fm.stringWithFileSystemRepresentation(result, length: Int(strlen(result)))
return tempDirectoryPath
}
It uses the same mkdtemp() BSD method as your original code. This method creates
a directory name from the template which is guaranteed not to exist at the time where
the method is called.
Thanks to Nate Cook who figured out that reinterpretCast() can be used to treat the UnsafePointer<CChar> returned by mkdtemp() as a CString, so that it can be passed to stringWithFileSystemRepresentation(), see Working with C strings in Swift, or: How to convert UnsafePointer<CChar> to CString.
As of Xcode 6 beta 6, the reinterpretCast() is not necessary anymore and the
above code can be simplified to
func tempDirectory()->String! {
let tempDirectoryTemplate = NSTemporaryDirectory() + "XXXXX"
var tempDirectoryTemplateCString = tempDirectoryTemplate.fileSystemRepresentation()
let result = mkdtemp(&tempDirectoryTemplateCString)
if result == nil {
return nil
}
let fm = NSFileManager.defaultManager()
let tempDirectoryPath = fm.stringWithFileSystemRepresentation(result, length: Int(strlen(result)))
return tempDirectoryPath
}