Does anyone know what's wrong with the code below? The this->progressBar1->Value part worked by the button_click_event but not in this snippet. I've been messing around with it but to no avail:
int Trouble ()
{
int hour = System::DateTime::Now.Hour;
this->progressBar1->Value = hour;
return 0;
}
This code snippet is part of a WinForm and it is located in the #pragma endregion part of my code (BTW This is Visual C++). As always I will apperciate any help or suggestions. Thanks!
It appears you've made this a free function rather than a member function of your class. Place this definition inside your class' definition (probably under the private: access modifier) and you'll get the behavior you expect. Also, do some reading on "scope", as it's a very fundamental concept and not understanding it is why you're having this problem.
I think this exchange of comments may qualify as an answer:
#Francis: Then you'll need to show more code, especially the function which calls Trouble. – Ben Voigt
There's no function that calls it; this code is stand-alone. – Francis Lau
So you can remove it from your code, and the program still compiles? – Ben Voigt
You may say that. – Francis Lau
That certainly explains why it doesn't "work". It's not sufficient to write a function, you also have to call it at an appropriate time.
Related
I am currently reviewing code written in c#, visual studio 2012.
In lot of places, the code is written using this key word, for ex:
this.pnlPhoneBasicDtls.Visible = true;
this.SetPhAggStats(oStats);
There are many other places where the controls of the page are referred using this key word.
Can somebody advise do we really need to use this here?
Any consequences of removing this keyword?
Thanks in advance..
No, "this" is optional. It's usually included in code generated by a tool and by people who feel the need to be explicit or who want to differentiate it from an argument to the method.
Its Optional you can use the
Property directly like pnlPhoneBasicDtls.Visible = true;
The this keyword is usually optional.
It's sometimes used to disambiguate fields from arguments if the same name is being used for both, for example:
void Main()
{
var sc = new SomeClass();
sc.SomeMethod(123);
Console.WriteLine(sc.thing);
}
public class SomeClass
{
public int thing;
public void SomeMethod(int thing)
{
this.thing = thing + 1;
}
}
In the example above it does make a difference. Inside SomeMethod, this.thing refers to the field and thing refers to the argument.
(Note that the simpler assignment thing = thing is picked up as a compiler error, since it is a no-op.)
Of course, if you use ReSharper then any unnecessary this. (together with unused using statements, unreachable code, etc.) will be greyed out and you can remove them very quickly. The same is probably true of similar tools like CodeRush.
I am wondering if there is a way to ignore certain TypeScript errors upon compilation?
I basically have the same issues most people with large projects have around using the this keyword, and I don't want to put all my classes methods into the constructor.
So I have got an example like so:
TypeScript Example
Which seems to create perfectly valid JS and allows me to get around the this keyword issue, however as you can see in the example the typescript compiler tells me that I cannot compile that code as the keyword this is not valid within that scope. However I don't see why it is an error as it produces okay code.
So is there a way to tell it to ignore certain errors? I am sure given time there will be a nice way to manage the this keyword, but currently I find it pretty dire.
== Edit ==
(Do not read unless you care about context of this question and partial rant)
Just to add some context to all this to show that I'm not just some nut-job (I am sure a lot of you will still think I am) and that I have some good reasons why I want to be able to allow these errors to go through.
Here are some previous questions I have made which highlight some major problems (imo) with TypeScript current this implementation.
Using lawnchair with Typescript
Issue with child scoping of this in Typescript
https://typescript.codeplex.com/discussions/429350 (And some comments I make down the bottom)
The underlying problem I have is that I need to guarantee that all logic is within a consistent scope, I need to be able to access things within knockout, jQuery etc and the local instance of a class. I used to do this with the var self = this; within the class declaration in JavaScript and worked great. As mentioned in some of these previous questions I cannot do that now, so the only way I can guarantee the scope is to use lambda methods, and the only way I can define one of these as a method within a class is within the constructor, and this part is HEAVILY down to personal preference, but I find it horrific that people seem to think that using that syntax is classed as a recommended pattern and not just a work around.
I know TypeScript is in alpha phase and a lot will change, and I HOPE so much that we get some nicer way to deal with this but currently I either make everything a huge mess just to get typescript working (and this is within Hundreds of files which I'm migrating over to TypeScript ) or I just make the call that I know better than the compiler in this case (VERY DANGEROUS I KNOW) so I can keep my code nice and hopefully when a better pattern comes out for handling this I can migrate it then.
Also just on a side note I know a lot of people are loving the fact that TypeScript is embracing and trying to stay as close to the new JavaScript features and known syntax as possible which is great, but typescript is NOT the next version of JavaScript so I don't see a problem with adding some syntactic sugar to the language as people who want to use the latest and greatest official JavaScript implementation can still do so.
The author's specific issue with this seems to be solved but the question is posed about ignoring errors, and for those who end up here looking how to ignore errors:
If properly fixing the error or using more decent workarounds like already suggested here are not an option, as of TypeScript 2.6 (released on Oct 31, 2017), now there is a way to ignore all errors from a specific line using // #ts-ignore comments before the target line.
The mendtioned documentation is succinct enough, but to recap:
// #ts-ignore
const s : string = false
disables error reporting for this line.
However, this should only be used as a last resort when fixing the error or using hacks like (x as any) is much more trouble than losing all type checking for a line.
As for specifying certain errors, the current (mid-2018) state is discussed here, in Design Meeting Notes (2/16/2018) and further comments, which is basically
"no conclusion yet"
and strong opposition to introducing this fine tuning.
I think your question as posed is an XY problem. What you're going for is how can I ensure that some of my class methods are guaranteed to have a correct this context?
For that problem, I would propose this solution:
class LambdaMethods {
constructor(private message: string) {
this.DoSomething = this.DoSomething.bind(this);
}
public DoSomething() {
alert(this.message);
}
}
This has several benefits.
First, you're being explicit about what's going on. Most programmers are probably not going to understand the subtle semantics about what the difference between the member and method syntax are in terms of codegen.
Second, it makes it very clear, from looking at the constructor, which methods are going to have a guaranteed this context. Critically, from a performance, perspective, you don't want to write all your methods this way, just the ones that absolutely need it.
Finally, it preserves the OOP semantics of the class. You'll actually be able to use super.DoSomething from a derived class implementation of DoSomething.
I'm sure you're aware of the standard form of defining a function without the arrow notation. There's another TypeScript expression that generates the exact same code but without the compile error:
class LambdaMethods {
private message: string;
public DoSomething: () => void;
constructor(message: string) {
this.message = message;
this.DoSomething = () => { alert(this.message); };
}
}
So why is this legal and the other one isn't? Well according to the spec: an arrow function expression preserves the this of its enclosing context. So it preserves the meaning of this from the scope it was declared. But declaring a function at the class level this doesn't actually have a meaning.
Here's an example that's wrong for the exact same reason that might be more clear:
class LambdaMethods {
private message: string;
constructor(message: string) {
this.message = message;
}
var a = this.message; // can't do this
}
The way that initializer works by being combined with the constructor is an implementation detail that can't be relied upon. It could change.
I am sure given time there will be a nice way to manage the this keyword, but currently I find it pretty dire.
One of the high-level goals (that I love) in TypeScript is to extend the JavaScript language and work with it, not fight it. How this operates is tricky but worth learning.
All,
Could you explain me about Monitor Class, esp following code in more detail?
if (Monitor.TryEnter(CashDrawers.lockObject))
{
try
{
// Work here
}
finally
{
Monitor.Exit(lockObject);
}
}
Thanks,
CK
Not sure if this is what you're looking for but...
The code you posted in your question is the non blocking version of
lock(CashDrawers.LockObject)
{
//work here
}
Meaning that it will only do it's "work" if it is able to acquire the lock on the first try. If something else already has the lock, then your code won't do anything. I'm assuming this code is written within the CashDrawers class, otherwise you probably have a transcription error in that you need to Moniter.Exit on the same object that you Entered on.
Are you looking for an explanation on synchronization in general? If so that's beyond the scope of what I can write in an answer. Please check out http://www.albahari.com/threading/part2.aspx for some general synchronization info in .net.
i was looking how to inject a dll into a program (exe, or dll, etc). i have been googleing dll injecting but i have not found anything that is very helpful :(. i have not worked with dlls very much so im not sure on what to do, i really could use some help on this.
uhh the only thing i have really found is setwindowshookex but i can't find any examples for it and i don't how to use it. any questions just ask and i'll try to help.
EDIT hey i was googling and this looks like something about dll injecting that is worth looking at but i can't get the code to run :\ (How to hook external process with SetWindowsHookEx and WH_KEYBOARD)
The method I'm most familiar with was is was described by Jefferey Richter in Programming Applications for Microsoft Windows. I mention this because even if you don't get your hands on the book itself there is probably sample code floating around. I think he may have also written some journal articles. He, also mentions a couple of alternative approaches, of which I will describe only one, from memory. He also may have written some MSJ / MSDN articles that are relevant.
Anyway, the basic idea is to cause the process that you want to load your DLL to issue a call to LoadLibrary. This is done using CreateRemoteThread with the address of LoadLibary for lpStartAddress and the address of a string naming your DLL in for lpParameter. Arranging for and locating the string is done using VirtualAllocEx to allocate some memory in the remote process, and WriteProcessMemory to fill it with the string.
PSEUDO CODE:
void InjectDllIntoProcess(DWORD processId, char *dllName)
{
HANDLE hRemoteProcess = OpenProcess(
// Assumes that dll and function addresses are the same in different processes
// on the same system. I think that this is true even with ASLR, only issue I
// can think of is to make sure that the source and target process are both 32
// or both 64 bit, not a mixture.
// Note that it is asking for the ASCII version
HMODULE hDll = LoadLibrary(_T("Kernel32.dll"));
void *loadLibAddr = GetProcAddress(hDll, _T("LoadLibraryA"));
// Inject the DLL name
char * remoteAddr =
(char *)VirtualAllocEx(hRemoteProcess, NULL, strlen(dllName) + 1, ...
WriteProcessMemory(hRemoteProcess, remoteAddr, dllName, strlen(dllName) + 1 ...
CreateRemoteThread(hRemoteProcess, ??, 0, loadLibAddr, remoteAddr, ...
}
I read this answer and its comments and I'm curious: Are there any reasons for not using this / Self / Me ?
BTW: I'm sorry if this has been asked before, it seems that it is impossible to search for the word this on SO.
Warning: Purely subjective answer below.
I think the best "reason" for not using this/self/me is brevity. If it's already a member variable/function then why redundantly add the prefix?
Personally I avoid the use of this/self/me unless it's necessary to disambiguate a particular expression for the compiler. Many people disagree with this but I haven't ever had it be a real sticking point in any group I've worked for.
I think most of the common scenarios have been covered in the two posts already cited; mainly brevity and redundancy vs clarity - a minor addition: in C#, it is required to use "this" in order to access an "extension method" for the current type - i.e.
this.Foo();
where Foo() is declared externally as:
public static void Foo(this SomeType obj) {...}
It clarifies in some instances, like this example in c#:
public class SomeClass
{
private string stringvar = "";
public SomeClass(string stringvar)
{
this.stringvar = stringvar;
}
}
If you use StyleCop with all the rules on, it makes you put the this. in. Since I started using it I find my code is more readable, but that's personal preference.
I think this is a non-issue, because it only adds more readability to the code which is a good thing.
For some languages, like PHP, it is even mandatory to prefix with $this-> if you need to use class fields or methods.
I don't like the fact that it makes some lines unnecessarily longer than they could be, if PHP had some way to reference class members without it.
I personally find that this.whatever is less readable. You may not notice the difference in a 2-line method, but wait until you get this.variable and this.othervariable everywhere in a class.
Furthermore, I think that use of this. was found as a replacement for a part of the much hated Hungarian notation. Some people out there found out that it's still clearer for the reader to see that a variable is a class member, and this. did the trick. But why fool ourselves and not use the plain old "m_" or simply "_" for that, if we need the extra clarity? It's 5 characters vs. 2 (or even 1). Less typing, same result.
Having said that, the choice of style is still a matter of personal preference. It's hard to convince somebody used to read code in a certain way that is useful to change it.
well, eclipse does color fields, arguments and local variables in different colors, so at least working in eclipse environment there is no need to syntactically distinguish fields in order to specially mark them as "fields" for yourself and generations to come.
It was asked before indeed, in the "variable in java" context:
Do you prefix your instance variable with ‘this’ in java ?
The main recurrent reason seems to be:
"it increases the visual noise you need to sift through to find the meaning of the code."
Readability, in other word... which I do not buy, I find this. very useful.
That sounds like nonsense to me. Using 'this' can make the code nicer, and I can see no problems with it. Policies like that is stupid (at least when you don't even tell people why they are in place).
as for me i use this to call methods of an instantiated object whereas self is for a static method
In VB.NET one of the common practice I use is the following code :
Class Test
Private IntVar AS Integer
Public Function New(intVar As Integer)
Me.Intvar = intvar
End Function
End Class
Not all the time but mostly Me / this / self is quite useful. Clarifies the scope that you are talking.
In a typical setter method (taken from lagerdalek's answer):
string name;
public void SetName(string name)
{
this.name = name;
}
If you didn't use it, the compiler wouldn't know you were referring to the member variable.
The use of this. is to tell the compiler that you need to access a member variable - which is out of the immediate scope of the method. Creating a variable within a method which is the same name as a member variable is perfectly legal, just like overriding a method in a class which has extended another class is perfectly legal.
However, if you still need to use the super class's method, you use super. In my opinion using this. is no worse than using super. and allows the programmer more flexibility in their code.
As far as I'm concerned readability doesn't even come into it, it's all about accessibility of your variables.
In the end it's always a matter of personal choice. Personally, I use this coding convention:
public class Foo
{
public string Bar
{
get
{
return this.bar;
}
/*set
{
this.bar = value;
}*/
}
private readonly string bar;
public Foo(string bar)
{
this.bar = bar;
}
}
So for me "this" is actually necessary to keep the constructor readable.
Edit: the exact same example has been posted by "sinje" while I was writing the code above.
Not only do I frequently use "this". I sometimes use "that".
class Foo
{
private string bar;
public int Compare(Foo that)
{
if(this.bar == that.bar)
{
...
And so on. "That" in my code usually means another instance of the same class.
'this.' in code always suggests to me that the coder has used intellisense (or other IDE equivalents) to do their heavy lifting.
I am certainly guilty of this, however I do, for purely vanity reasons, remove them afterwards.
The only other reasons I use them are to qualify an ambiguous variable (bad practice) or build an extension method
Qualifying a variable
string name; //should use something like _name or m_name
public void SetName(string name)
{
this.name = name;
}