View,
immediately before the existing method
draw(_:).
required init(coder aDecoder: NSCoder) { super.init(coder: aDecoder)!; //Background can't be set in draw(_:). backgroundColor = UIColor.yellow; }
draw(_:)
method of class
View,
we can change
let point: CGPoint = CGPoint(x: 0.0, y: 0.0);to
let point: CGPoint = CGPoint.zero;or even to
let point: CGPoint = .zero;
CGPoint.zero
is a constant, predefined
CGPoint
structure that always contains 0, 0.
In fact, we can use
CGPoint.zero
in place of our variable
point
as the first argument of
draw(at:withAttributes:):
s.draw(at: CGPoint.zero, withAttributes: nil);or
s.draw(at: .zero, withAttributes: nil);See also
CGSize.zero
and
CGRect.zero.
draw(_:)
method of class
View,
change the original
let point: CGPoint = CGPoint(x: 0.0, y: 0.0);to the following. The
safeAreaLayoutGuide
property of class
UIView
is an object of class
UILayoutGuide.
safeAreaLayoutGuide
therefore contains a property of class
CGRect
named
layoutFrame.
This rectangle is the part of the
UIView
that is not covered by the status bar and the other bars.
let point: CGPoint = CGPoint(x: 0.0, y: safeAreaLayoutGuide.layoutFrame.origin.y);
The value of the
y
property of the
origin
property of the
layoutFrame
property of the
safeAreaLayoutGuide
property of the
UIView
is 44,
which is the height of the status bar in pairs of pixels
(at least on iPhone XR in portrait orientation).
You can verify this by changing the variable
s.
let s: String = "Height of status bar is \(safeAreaLayoutGuide.layoutFrame.origin.y) pairs of pixels.";
Height of status bar is 44.0 pairs of pixels.
The height of the status bar is therefore 88 pixels. You can verify this by examining a screenshot in the Preview application.
Bonus:
the
y
of the
safeAreaLayoutGuide
will be zero if we hide the status bar.
The status bar is hidden automatically in landscape orientation.
In the Simulator, pull down
Hardware → Rotate Right
We can also hide the status bar in portrait orientation.
In the Xcode
Project Navigator,
select the property list file
Info.plist.
We will
add
two properties to this file.
- Point at the bottom property (which is probably named “Supported interface orientations”) and two circles will appear, containing a plus sign and a minus sign. Click on the plus sign to create a new property. Click on the left pair of small up and down triangles to select the name “Status bar is initially hidden” for this new property. Click on the right pair to select YES as the value for this property.
- Then add one more property, with the name “View controller-based status bar appearance” and the value NO.
(You can see your two new properties in XML by control-clicking on
Info.plist
in the
Project
Navigator
and selecting Open As → Source Code.)
Run the app again.
Then recover the status bar by deleting these two properties.
View.
In the
draw(_:)
method of class
View,
change the original
let point: CGPoint = CGPoint(x: 0.0, y: 0.0);to the following.
size(withAttributes:)
returns the
size
of a piece of text.
bounds.origin
is the
point
at the upper left corner of the big yellow
View.
bounds.size
is the size of the big yellow
View.
As always, our
point
variable will be the location of the upper left corner of the text.
let size: CGSize = s.size(withAttributes: nil); let x: CGFloat = bounds.origin.x + (bounds.size.width - size.width) / 2; let y: CGFloat = bounds.origin.y + (bounds.size.height - size.height) / 2; let point: CGPoint = CGPoint(x: x, y: y);
draw(_:)
method of class
View,
let font: UIFont = UIFont.systemFont(ofSize: 36); let foregroundColor: UIColor = UIColor.red; //a two-line dictionary let attributes: [NSAttributedString.Key: Any] = [ NSAttributedString.Key.font: font, NSAttributedString.Key.foregroundColor: foregroundColor ];Then replace the
nil
parameter of
draw(at:withAttributes:)
and
size(withAttributes:)
with your new
attributes.
For example,
s.draw(at: point, withAttributes: attributes);
You can concoct your own foreground and background colors:
//mauve, opaque let foregroundColor: UIColor = UIColor(red: 0.878, green: 0.690, blue: 1.0, alpha: 1.0);
"Hello, World!"
to a string in a foreign character set.
let s: String = "هزا مدهش"; //That's amazing!
You can copy and paste the above text.
Or to type it yourself,
click on a point within the double quotes, and then pull down
Edit → Emoji & Symbols…
Click on the rectangular icon in the upper right corner
if necessary to expand the Emoji & Symbols window.
Then pull down the gear in the upper left corner,
select Customize List…,
and open Middle Eastern Scripts.
draw(_:)
method of class
View,
change
let s: String = "Hello, World!";to one of the following.
//There is always exactly one object of class UIDevice. //The object is therefore a singleton. let device: UIDevice = UIDevice.current; let s: String = device.model; //"iPhone", "iPad", "iPod touch" let s: String = device.identifierForVendor!.uuidString; //serial number, e.g., "F976349D-7E34-4816-8EEA-CABC2ACB84E9" let s: String = device.systemName; //name of operating system, e.g. "iPhone OS" let s: String = device.systemVersion; //version number of operating system, e.g., "12.2"
draw(_:)
method of class
View,
change
let s: String = "Hello, World!";to the following. The format
sl1t1d1
is the concatenation of
s
(lowercase S),
l1
(lowercase L one),
t1
(lowercase T one),
d1
(lowercase D one);
see the list of
Yahoo formats.
The
init(string:)
method of class
URL
indicates an error by returning
nil.
The
init(contentsOf:encoding:
method of class
String
indicates an error by throwing an
Error.
See
Catching
and Handling an Error.
var s: String; let url: URL? = URL(string: "http://finance.yahoo.com/d/quotes.csv?s=IBM&f=sl1t1d1"); if url == nil { s = "malformed URL"; } else { do { s = try String(contentsOf: url!, encoding: String.Encoding.utf8); } catch { s = String(describing: error); //error is an Error. } }
The Xcode Debug Area will display the following error:
2017-10-21 08:41:54.792792-0400 Hello[1789:47359] App Transport Security has blocked a cleartext HTTP (http://) resource load since it is insecure. Temporary exceptions can be configured via your app's Info.plist file. 2017-10-21 08:41:54.792961-0400 Hello[1789:47361] NSURLConnection finished with error - code -1022
and the app will display the following.
Switch to a smaller font,
or rotate the iOS Simulator to landscape orientation:
Hardware →
Rotate Right
Error Domain=NSCocoaErrorDomain Code=256
"The file “quotes.csv” couldn’t be opened."
UserInfo={NSURL=http://finance.yahoo.com/d/quotes.csv?s=IBM&f=sl1t1d1}
You will also have to
add
the
App
Transport Security
property to the
Info.plist
file.
Since the value of this property is an entire dictionary,
not merely a YES or a NO,
the easiest way to add it is to
control-click on
Info.plist
in the
Project Navigator,
select Open As → Source Code,
and insert the following property immediately before the
</dict> </plist>at the bottom of the file.
<key>NSAppTransportSecurity</key> <dict> <key>NSAllowsArbitraryLoads</key> <false/> <key>NSExceptionDomains</key> <dict> <key>finance.yahoo.com</key> <dict> <key>NSIncludesSubdomains</key> <true/> <key>NSTemporaryExceptionAllowsInsecureHTTPLoads</key> <true/> <key>NSTemporaryExceptionMinimumTLSVersion</key> <string>TLSv1.1</string> </dict> </dict> </dict>To take a screenshot of part of the Xcode window, see How to take a screenshot of a selected portion of your screen.
The time zone is Eastern:
"IBM",162.07,"4:01pm","10/20/2017"
draw(_:)
method of class
View,
change
let s: String = "Hello, World!";to the following.
//an array of 7 Strings, indexed by a UIDeviceOrientation let orientations: [String] = [ "Unknown", "Portrait", //home button at bottom "PortraitUpsideDown", //home button at top "LandscapeLeft", //home button on right "LandscapeRight", //home button on left "FaceUp", "FaceDown" ]; let device: UIDevice = UIDevice.current; let orientation: UIDeviceOrientation = device.orientation; let s: String = orientations[orientation.rawValue];Even better, let the above constants
orientations
and
device
be
stored
properties
of class
View.
To get to
PortraitUpsideDown,
see the
ViewController
example.
draw(_:)
method of class
View,
change
let s: String = "Hello, World!";to the following.
let date: Date = Date(); //holds the current date and time let s: String = date.description; //or date.description(with: .current);
Run the app and note that the time is updated whenever you change the orientation of the device from portarit to landscape and back again.
2018-10-28 12:49:24 +0000
Sunday, October 28, 2018 at 8:49:24 AM Eastern Daylight Time
Then append the following statements to
draw(_:)
and run the app again.
The code enclosed in the
{curly braces}
is a
closure.
//Call draw(_:) once per second. One second equals 1000 milliseconds. let oneSecond: DispatchTimeInterval = DispatchTimeInterval.milliseconds(1000); let now: DispatchTime = DispatchTime.now(); let oneSecondFromNow: DispatchTime = now + oneSecond; //Call the setNeedsDisplay method of this View object one second from now. //setNeedsDisplay will trigger a call to the draw(_:) method of this View object. DispatchQueue.main.asyncAfter(deadline: oneSecondFromNow) { self.setNeedsDisplay(); }
draw(_:)
once every 33 milliseconds,
i.e.,
approximately 30 times per second.
//Call draw(_:) every 33 milliseconds. let interval: DispatchTimeInterval = DispatchTimeInterval.milliseconds(33); DispatchQueue.main.asyncAfter(deadline: DispatchTime.now() + interval) { self.setNeedsDisplay(); }Add the following stored property to class
View.
To make it a stored property,
insert it immediately after the line that says
class View: UIView {.
You’ll have to remove
the
y
variable you added in the above exercise 3.
//the y coordinate of the point where the text will be printed var y: CGFloat = 0.0;Change the
CGPoint
to
let point: CGPoint = CGPoint(x: 0.0, y: y);And just before calling
asyncAfter(deadline:),
add 1 to
y:
y += 1; //means y = y + 1;Can you get the text to move from left to right? How about diagonally?
draw(_:)
every 33 milliseconds.
Replace the
y
property of class
View
with the following property.
//Increases at the rate of 2 * pi per 3 seconds. var x: Float = 0;Change the
CGPoint
to
let point: CGPoint = CGPoint(x: 0.0, y: bounds.size.height / 2 + CGFloat(sin(x)) * bounds.size.height / 4);Change the name of the stored property from
y
to
x,
and change the
y += 1;
to
x += 2 * CGFloat.pi * 33 / 1000;
x
of class
View.
Get rid of the bobbing
by going back to the original
CGPoint
of plain old constant 0, 0.
Change the dictionary of attributes to the following.
The return value of
sin
must be converted to the data type
CGFloat
demanded by the
init
method of class
UIColor.
//alpha goes from 0 to 1 and back again every 3 seconds. let foregroundColor: UIColor = UIColor(red: 0.0, green: 0.0, blue: 0.0, alpha: 0.5 + CGFloat(sin(x)) / 2); let attributes: [NSAttributedStringKey: Any] = [ NSAttributedStringKey.font: font, NSAttributedStringKey.foregroundColor: foregroundColor ];
x
property of class
View.
At the top of
View.swift,
after the existing
import,
insert
import CoreLocation; //for CLLocationDegreesAdd the following property to class
View
immediately after the line that says
class View: UIView {.
var temperature: Double?; //in Fahrenheit, an optional DoubleInsert the following code into the
init(coder:)
method of class
View
after setting the background color.
let apiKey: String = "92a0b81218fc51a38a717d1aed2b4a22"; //New York City let latitude: CLLocationDegrees = 40.78; //north latitude is positive let longitude: CLLocationDegrees = -73.97; //west longitude is negative let url: URL? = URL(string: "https://api.forecast.io/forecast/\(apiKey)/\(latitude),\(longitude)"); if url == nil { print("could not create URL"); return; } let sharedSession: URLSession = URLSession.shared; let downloadTask: URLSessionDownloadTask = sharedSession.downloadTask( with: url!, completionHandler: {(filename: URL?, response: URLResponse?, error: Error?) -> Void in if (error != nil) { print("could not download data from server: \(error!)"); return; } //Arrive here when the data from the forecast server has been //downloaded into a file in the device. //Copy the data from the file into a Data object. let data: Data; do { data = try Data(contentsOf: filename!); } catch { print("could not create Data object"); return; } //The data is in JSON format. //Copy the data from the Data object into a big Swift dictionary. let dictionary: [String: Any]?; do { try dictionary = JSONSerialization.jsonObject(with: data, options: JSONSerialization.ReadingOptions()) as? [String: Any]; } catch { print("could not create big dictionary: \(error)"); return; } //The big dictionary contains a smaller one. Let's name it "currently". let currently: [String: Any]? = dictionary!["currently"] as? [String: Any]; if currently == nil { print("big dictionary does not contain the key \"currently\""); return; } //The "currently" dictionary contains the current temperature. self.temperature = currently!["temperature"] as? Double; if self.temperature == nil { print("The \"currently\" dictionary does not contain the key \"temperature\""); return; } //Now that we have the temperature, call draw(_:). DispatchQueue.main.async(execute: {() -> Void in self.setNeedsDisplay(); }); }); downloadTask.resume();In
draw(_:),
create the string
s
as follows.
To type the degree sign °,
Edit → Emoji & Symbols → Punctutation
Left justify the string as in exercise 2 above.
var s: String; if temperature == nil { s = "temperature"; //haven't heard from the server yet } else { s = "temperature \(temperature!)° F"; }Remove the call to
async(execute:).
How many times is
draw(_:)
called?
How long is the interval between the calls?
- When creating the project, select Language: Objective-C.
- Instead of dragging the file
View.swiftto a position immediately belowViewController.swift, drag the two filesView.handView.mto a position immediately belowViewController.m. - In the View’s Identity Inspector, the class should be View but the Module should be the empty string.
- In the file
View.m, uncomment the methoddrawRect:and paste the following code under the “Drawing code” comment.NSString *s = @"Hello, World!"; CGPoint point = CGPoint(x: 0.0, y: 0.0); UIFont *font = [UIFont systemFontOfSize: 32.0]; NSDictionary *attributes = [NSDictionary dictionaryWithObject: font forKey: NSFontAttributeName]; [s drawAtPoint: point withAttributes: attributes];
- Paste the following method above
drawRect:but below the@implementationline.- (id) initWithCoder: (NSCoder *) coder { self = [super initWithCoder: coder]; if (self) { // Initialization code self.backgroundColor = [UIColor yellowColor]; } return self; }