I'm trying to call an instance method from a class method in Swift, but I keep getting the error "Missing argument for parameter #1 in call" on the "someMethod()" call.
Do you know why?
Here's the code:
class ViewController: UIViewController {
class func updateData() {
someMethod()
}
func someMethod() {
NSLog("someMethod")
}
}
updateData is declared as a class method (i.e. static), and it's executed in the context of the class type and not a class instance. On the other hand, someMethod is an instance method.
You cannot execute an instance method from a static method, unless you provide an instance.
Without knowing the logic of your app, it's hard to figure out how the problem should be solved. Some possible solutions:
make uploadData an instance method, by removing class from its signature:
func updateData() { ...
make someMethod a static method:
class func someMethod() { ...
Related
I have a protocol declared in a class
public protocol demoDelegate {
func willShowdemoResult(DemoGraph: UIView)
}
Now I am calling this in the same class where the protocol is declared.
public class Demo:UIViewController {
public var delegate : demoDelegate!
//some code
self.delegate.willShowdemoResult(self.demoGraph())
}
where demo graph returns a UI graph
func demoGraph() -> UIView {
//some code
return demoGraphView
}
I am getting an error that unexpectedly found nil while wrapping an optional value. I know the reason that I have not initialised the delegate. Can somebody guide me How to initialise the delegate here.
The function is being called in other class
class DemoResult: UIViewController, demoDelegate{
func willShowdemoResult(DemoGraph: UIView)
// some code
}
Please Help
You are getting the error, because Demo.delegate is nil when calling:
delegate.willShowdemoResult(self.demoGraph())
Before you make this call, make sure, that you have set the delegate property. I would recommend this right after initializing Demo or right after DemoResult got the address of the Demo-instance.
Let's assume, you have stored an instance of Demo in DemoResult.demoVC. Then you can set the delegate in DemoResult like this:
demoVC.delegate = self
BTW: It's better to use optional types to store delegates:
public var delegate: demoDelegate?
When delegate is optional, delegate?.willShowdemoResult(self.demoGraph()) won't crash, if delegate has not been initialized yet.
I have a class TestClass and a class & instance method inside it
class TestClass {
class func classMethod(){
print("how do i call instance method from here")
}
func instanceMethod(){
print("call this instance method")
}
}
My question is how do i call that instanceMethod from classMethod??
One way i have noticed is
class func classMethod(){
TestClass().instanceMethod()
}
But,Is this the good way to do?
What you are trying to do rarely makes any sense from a design perspective.
By definition, an instance method operates on an instance of an object.
For example, it might require access to some instance members, or somehow meddle with the state of the object you call the method on.
class methods on the other hand do not require an instance to be able to call them - and should in general only operate on the given parameters, not be dependant on shared state.
If you need to call instanceMethod() in classMethod(), and instanceMethod() does not require any state - why is it not also a class method, or a (global) pure function?
You can pass the instance object as a parameter to the class method, and then call the instance method of the object:
class TestClass {
class func classMethod(obj:TestClass){
print("how do i call instance method from here")
obj.instanceMethod()
}
func instanceMethod(){
print("call this instance method")
}
}
To call the instance method, you need an instance of TestClass. That's what TestClass() is getting you when you call TestClass().instanceMethod().
If you want to call it from a specific instance, you could pass it in as a parameter to the class function: class func classMethodUsingInstance(instance: TestClass)
If you don't need a specific instance for instanceMethod(), maybe consider making it a class method as well.
I'm writing a factory class that is trying to work with custom protocol defined functions. The compiler throws an error, because I don't know how to add a protocol definition to a function parameter.
Example:
protocol MyCustomFunctions {
func customFunction()
}
class MyVC: UIViewController, MyCustomFunctions {
func customFunction() {}
}
class Factory {
func createButton(specificVC: UIViewController) // need protocol here
{
specificVC.customFunction() // error thrown
}
}
How can one specific a protocol during a variable definition?
Or is there another way?
First of all ,convention says classes start with a Capital letter.
class MyVC: UIViewController, MyCustomFunctions {
func customFunction() {}
}
Then what you need is the correct type in the argument
class factory: NSObject {
func createButton(specificVC: MyVC) // you need a class that conforms to protocol here.
{
specificVC.customFunction() // no error anymore
}
}
You have another option. You can simply promise in the argument that you won't disclose the full type of the object ,you will only say it's an opaque object that conforms to protocol.
class factory: NSObject {
func createButton(specificVC: MyCustomFunctions) // you need a class that conforms to protocol here.
{
specificVC.customFunction() // no error anymore
}
}
BONUS:
The way you could have reasoned about this and find an answer is this>
Error is thrown when I call specificVC.customFunction()...Hmmm...so this object can only run this function if it is of type that actually HAS the function. So let's take a look at the argument type - UIViewController - ..UIViewController certainly doesn't have this function. It's the MyVC or the Protocol.
Type safety in Swift is very strict. Just "follow the type flow" and you will be good.
In a custom subclass of GroupOperation, I'm trying to override operationDidFinish(). When I attempt to implement the function in my subclass, I get this error message:
Method does not override any method from its superclass
If I remove the override keyword, I get
Method 'operationDidFinish(:withErrors:)' with Objective-C selector
'operationDidFinish:withErrors:' conflicts with method
'operationDidFinish(:withErrors:)' from superclass 'GroupOperation'
with the same Objective-C selector
Weirdness. I'm pretty sure my method signature is spot on, and I'm not trying to overload an obj-c method, so all should be well. What gives?
For reference, my class looks like this:
class ServerAuthenticationOperation: GroupOperation {
// properties... initializer stuff...
override func operationDidFinish(operation: NSOperation, withErrors errors: [NSError]) {
print("I finished!")
}
}
I assume you're using Swift 2.
Objective-C does not support method overloading, so you have to select a different name for your method. Or, you can try these options:
Rename the method using the #objc(newMethodName:)
Use #nonobjc
Edit:
It seems working for the repo you provided, you can check it here. https://www.dropbox.com/s/hb07u3hyjhjuews/OverrideTest.zip?dl=0
I have following protocol:
#objc protocol SomeProtocol {
func someMethod()
}
and then some class conforming to that protocol:
class SomeClass: SomeProtocol {
...
func someMethod() {
// do something
}
}
My question: how to test (I'm testing in Objective-C with OCMock) that e.g. method call written in someMethod() implemented by SomeClass is actually called?
Many thanks.
I'm not that knowledgeable in Swift, so I cannot give you a completely accurate answer, however, for Obj-C, I do something like this:
id mockDelegate = OCMProtocolMock(#protocol(CallViewControllerDelegate));
self.cVC.delegate = mockDelegate;
OCMExpect([mockDelegate callOutcomeSuccessful:OCMOCK_ANY]);
OCMVerifyAll(mockDelegate);
With this, you set up an expectation for a mock delegate object, on which you can later verify the call to the delegate method.