null

问题 Is it possible to somehow shorten this statement? if (obj != null) obj.SomeMethod(); because I happen to write this a lot and it gets pretty annoying. The only thing I can think of is to implement Null Object pattern, but that's not what I can do every time and it's certainly not a solution to shorten syntax. And similar problem with events, where public event Func<string> MyEvent; and then invoke if (MyEvent != null) MyEvent.Invoke(); 回答1: From C# 6 onwards, you can just use: MyEvent?.Invoke

问题 This seems odd to me -- VB.NET handles the null check implicitly via its RaiseEvent keyword. It seems to raise the amount of boilerplate around events considerably and I don't see what benefit it provides. I'm sure the language designers had a good reason to do this.. but I'm curious if anyone knows why. 回答1: It's certainly a point of annoyance. When you write code which accesses a field-like event within a class, you're actually accessing the field itself (modulo a few changes in C# 4; let's

问题 See this playground: http://play.golang.org/p/nWHmlw1W01 package main import "fmt" func main() { var i []int = nil yes(i) // output: true no(i) // output: false } func yes(thing []int) { fmt.Println(thing == nil) } func no(thing interface{}) { fmt.Println(thing == nil) } Why the difference in output between the two functions? 回答1: Admittedly, it's somewhat of a quirk, but there's an explanation for it. Imagine an interface{} variable as a struct composed of two fields: one is the type and

问题 I am trying to understand the behavior of the @() array constructor, and I came across this very strange test. It seems that the value of an empty pipeline is "not quite" the same as $null, even though it is -eq $null The output of each statement is shown after the ### $y = 1,2,3,4 | ? { $_ -ge 5 } $z = $null if ($y -eq $null) {'y is null'} else {'y NOT null'} ### y is null if ($z -eq $null) {'z is null'} else {'z NOT null'} ### z is null $ay = @($y) $az = @($z) "ay.length = " + $ay.length ##

问题 I know declared property generates accessor method which is someway just syntax sugar. I found quite a lot people use self.property = nil in their dealloc method. 1) In Apple's Memory Management document, p23 It says: The only places you shouldn’t use accessor methods to set an instance variable are in init methods and dealloc. why shouldn't? 2) In apple's Objective-C 2.0 , p74 Declared properties fundamentally take the place of accessor method declarations; when you synthesize a property,

问题 Can I simply use if(myString == nil) For some reason a string that I know is null, is failing this statement. 回答1: Is it possible that your string is not in fact nil , and is instead just an empty string? You could try testing whether [myString length] == 0 . 回答2: You can find more on objective C string here. + (BOOL ) stringIsEmpty:(NSString *) aString { if ((NSNull *) aString == [NSNull null]) { return YES; } if (aString == nil) { return YES; } else if ([aString length] == 0) { return YES;

问题 Often I have a class as such: public class Foo { private String field1; private String field2; // etc etc etc } This makes the initial values of field1 and field2 equal to null. Would it be better to have all my String class fields as follows? public class Foo { private String field1 = ""; private String field2 = ""; // etc etc etc } Then, if I'm consistent with class definition I'd avoid a lot of null pointer problems. What are the problems with this approach? 回答1: I disagree with the other

问题 Given that collections like System.Collections.Generic.HashSet<> accept null as a set member, one can ask what the hash code of null should be. It looks like the framework uses 0 : // nullable struct type int? i = null; i.GetHashCode(); // gives 0 EqualityComparer<int?>.Default.GetHashCode(i); // gives 0 // class type CultureInfo c = null; EqualityComparer<CultureInfo>.Default.GetHashCode(c); // gives 0 This can be (a little) problematic with nullable enums. If we define enum Season { Spring,

问题 So I thought I had all these questions all figured out. Then all of a sudden I get an error (a crash) I can't figure out. Then after doing research to remedy the crash, I notice everything that I thought I knew about these critical areas are somewhat wrong. Below are 8 questions I am just going to shoot out there in hopes of somebody answering - the answers to these will greatly help me get my understanding back on track. Thanks ahead of time! Q1) Is it okay to call Release on an object if

问题 I have a storyviewcontroller which has objects on its view. I need to change the text on the UILabel(In the storyviewcontroller) and the load the view on an array. I have connected the IBOutlet to the label in the storyviewcontroller. class StoryViewController: UIViewController { @IBOutlet weak var textLabel: UILabel! @IBOutlet weak var inspiredButton: UIButton! I have created an object of the storyviewcontroller class and am able to access its variables. However, after creating the object of