I'm working in java me. I created two visual designs, First.java and Second.java both of which contains form displayables.
I added an Ok command to a form in First.Java and the user is expected to switch to SecondForm in Second.java but I get this error non-static method getSecondForm() cannot be referenced from a static context.
How can I fix this?
Both files are in the same package. Here's the source code
public void commandAction (Command command, Displayable displayable) {
if (displayable == firstForm) {
if (command == exitCommand) {
exitMIDlet();
} else if (command == okCommand) {
switchDisplayable(null, Second.getSecondForm());
}
}
}
You need to change declaration of the method getSecondForm in Second.java to make it static.
If it currently looks like
Displayable getSecondForm() //... whatever code is there
then after change it should look like
static Displayable getSecondForm() //... whatever code is there
Note above change will fix the non-static method getSecondForm... error you mentioned but there is a chance that it will cause new compilation errors in file Second.java. You will need to fix these new errors, most likely by adding couple static keywords here and there, similar to how it is shown above.
Note this is java language basic stuff; if you get stuck fixing this, consider taking a break to study some tutorial for beginners.
Related
I have a parent component and a child component with an event callback where I want it to pass back a type of T.
The issue I'm having is that I have an error about converting
MethodGroup to EventCallback.
If I convert this to using an Action then it works, but I can't do it async which isn't ideal.
Any ideas what I'm doing wrong?
Parent
<Child DeleteCallback="#OnDelete"></Child>
public async Task OnDelete(T item)
{ ... }
Child
#typeparam T
[Parameter]
public EventCallback<T> DeleteCallback { get; set; }
<a #onclick="() => DeleteCallback.InvokeAsync(item)"></a>
I've added a repo here explaining the problem. Looking at the Issues for Blazor, this should;ve been fixed in 2019. https://github.com/scott-david-walker/EventCallbackError
You were close:
<ChildComponent Item="someModel" T="SomeModel" DeleteCallback="OnDeleteSomeModel" />
#code {
SomeModel someModel = new SomeModel();
void OnDeleteSomeModel(SomeModel someModel)
{
...
}
}
The EventCallback uses a generic type and blazor cannot infer it if you don't pass the type to the component.
This means that if you have a EventCallback<T> you need to pass the value of T to the component e.g. T="SomeType".
In my case I declared a nullable EventCallback? - you can't do that.
I've experienced that the syntax was spot on and still getting this error.
Restarting Visual Studio 2019 solved the problem for me. Cleaning and rebuilding was not enough.
For some reason Visual Studio kept a previous signature I had used. Cleaning, restarting, emptying bin/obj folders etc did not work. I had to rename the method, which worked for me.
The following syntax worked for me:
// in the component (C#):
[Parameter]
public EventCallback<MovingEventArgs> OnMoving { get; set; }
// on the using side (Razor):
OnMoving="(Component.MovingEventArgs o) => OnMoving(o)"
// on the using side (C#):
protected void OnMoving( Component.MovingEventArgs e ) {
}
There seems to have been a change and the documentation is not up to date.
This event is also using custom event arguments.
For anyone fighting this with the MudBlazor MudTable I found this worked use #bind-SelectedItem and don't pass any parameters to the commit function.
<MudTable T="POCO" Items="#MyState.POCOs"
#bind-SelectedItem="_selectedPOCO"
OnCommitEditClick="#(() => commitPOCO())"
CommitEditTooltip="Save Changes?">
#code {
private POCO _selectedPOCO;
private async void commitPOCO()
{
// all the changed values are in _selectedPOCO
...
}
In my case, the problem solved when I defined the #typeparam manually(not by inference)(TItem="int").
<MyComponent TItem="int" OnChange="Component_Changed" />
Okay I just spent hours trying to figure this out. Turns out on my end the problem was I have sync fusion in the project and I had explicitly define the name space of the Event call back arguments which in my case were Microsoft.AspNetCore.Components.ChangeEventArgs in the child component and then creating an async method to pass back data to the parent.
In my case it was a phantom error among tens others that never went away no matter what I do. Meaning I could still build and run a solution without problems, despite so many erorrs.
What helped me was this solution: https://stackoverflow.com/a/66219566/1215913
However, I finally found a solution after a few hours of digging. To
get rid of the phantom errors I closed Visual Studio, deleted the
files in the following folder, and then re-opened the solution:
C:\Users<Username>\AppData\Local\Temp\VSFeedbackIntelliCodeLogs\Suggestions\
The only difference is I removed all of the folders that start with VS (C:\Users\<Username>\AppData\Local\Temp\VS*) since there was no this exact path as #rovert mentions in his post.
This seems to be some common problem with Blazor and IntelliSense. I also often see that auto-formatter fails to correctly format the razor code (text indentations are a mess).
In my case I got the error
Error (active) CS1503 Argument 2: cannot convert from 'method group'
to 'EventCallback'
for ValueChanged with the following code:
<MatAutocompleteList TItem="UseCase" Items="#selectUseCases" ValueChanged=#SelectUseCases>
<ItemTemplate>
#context?.Label
</ItemTemplate>
</MatAutocompleteList>
#code
{
private UseCase SelectUseCases(UseCase useCaseDto)
{
if (useCaseDto != null)
{
//Do stuff
}
return null;
}
}
Changed to private void SelectUseCases(UseCase useCaseDto), removed all returns and the error disappeared.
After trying all other solutions proposed here, including:
Making sure I was providing T=myType
Clean and rebuild
Restart Visual Studio
Rename the method by appending a letter to its name and aligning its binding
The only thing that worked for me was literally deleting the line with the binding, saving, recompiling, then writing it back.
In doing so, I in fact realized that I was typing:
SelectedItemChanged="#SelectedItemsChanged"
instead of:
SelectedItemsChanged="#SelectedItemsChanged"
I was missing an s in the binding. The method itself had a signature receiving a HashSet of my type, so it could only deal with Items, not a single item.
One would think that in C# 8.0 you should be able to do the following (according to this (1st snippet)):
public interface IRestApiClient : IRestClient
{
...
Task<T> PostPrivateAsync<T>(string action, OrderedDictionary<string, object> parameters = null, DeserializeCustom<T> deserializer = null)
{
return QueryPrivateAsync(Method.POST, action, parameters, deserializer);
}
...
}
public class SpecificClient : ExchangeClient, IRestApiClient, IRestHtmlClient, ISeleniumClient, IWebSocketClient
{
}
The example above won't compile because the interface members need to be explicitly and wholly implemented (including the methods supplying the default logic)
So one would think that the following should work:
public interface IRestApiClient : IRestClient
{
...
Task<T> PostPrivateAsync<T>(string action, OrderedDictionary<string, object> parameters = null, DeserializeCustom<T> deserializer = null)
{
return QueryPrivateAsync(Method.POST, action, parameters, deserializer);
}
...
}
public class SpecificClient : ExchangeClient, IRestApiClient, IRestHtmlClient, ISeleniumClient, IWebSocketClient
{
...
public async Task<T> PostPrivateAsync<T>(string action, OrderedDictionary<string, object> parameters = null, DeserializeCustom<T> deserializer = null)
=> await ((IRestApiClient) this).PostPrivateAsync(action, parameters, deserializer);
...
}
Nope, it looks like this method is recursive (despite the upcast) and will cause our favorite Stack Overflow exception.
So my question is (abstracting from the fact that I could change the design in my example), is there a way of keeping the implementation for a specific method default, preferably without the necessity of resorting to hacky or Static Helper Extension methods? I could call static extension method in both interface and the class but it kind of defeats the purpose of this feature.
// EDIT
I must admit it confuses me and it appears I am missing something critical that is obvious to other people. I didn't provide additional info because I didn't consider my issue to be code specific. Lets look at this simple example (taken from the website I linked on the beginning of my post):
According to #Panagiotis Kanavos comment: No, default members don't need to be implemented (...) what I screenshoted should not be true. Can sb please enlighten me?
// EDIT 2
As you can see I am properly targeting .NET CORE 3.0 with C# 8.0.
ERRORS:
Interface method cannot declare a body
Interface member 'void CryptoBotCoreMVC.IDefaultInterfaceMethod.DefaultMethod()' is not implemented
To answer the question in the comments: I didn't specify LangVersion explicitly in the .csproj file.
// EDIT 3
The issue was ReSharper, see:
https://stackoverflow.com/a/58614702/3783852
My comment have been deleted, presumably by the owner of the answer so I'll write it here: the clue was the fact that there was actually no error numbers, but the compilation was blocked. It turned out that there is an option to block compilation when these errors occur in ReSharper.
It seems that in the end this is a possible duplicate, but getting to this conclusion was quite a journey :).
The issue is caused by ReSharper, reference:
https://youtrack.jetbrains.com/issue/RSRP-474628
It appears that the problem will be resolved in version v2019.3 and we currently have v2019.2.3. You can setup ReSharper to block compilation depending on issue severity, the workaround is to disable this feature for the time being.
Is it possible to create a code refactoring for ReSharper like the one that checks a parameter for null.
This will generate the following guard check if we apply that to the method below
public void Method(string value)
{
if (value == null) throw new ArgumentNullException(nameof(value));
}
Is it possible to create a refactoring like "Check string parameter for not null or white space" that will be suggested on string parameters only?
public void Method(string value)
{
if (string.IsNullOrWhiteSpace(value)) throw new ArgumentNullException(nameof(value));
}
That is possible using context action. I don't know with what exact version this was introduced, but at least with 2016.1 it should be there.
Besides that, you can use live templates for some needs. They have some limitations though. If you reach them, you can create a custom plugin that implements a context action for instance.
My application is built in MFC.After the application executes I need to open the help file provided with exe.
But as I press F1 application gives an error message saying the file cannot be found. This happens because no such file of that name exist.
One would think how about changing the name of help file itself? well that cannot be done I have to change the path as well.
I need to know how does the function of F1 button work and where can I find the same?
I am using VC++ 6.0 (I know its very old, but I am stuck with it).
Thank you.
To show your specific help file, you have to overwrite CWinApp::OnHelp. The path to the standard help file is stored in CWinApp::m_pszHelpFilePath. In this example, I use my own m_path variable.
void CMyApp::OnHelp()
{
::HtmlHelp(((CMainFrame*)AfxGetMainWnd())->m_hWnd,m_path,HH_DISPLAY_TOPIC,NULL);
}
If I remember correctly, by default it's handled by CWinApp::OnHelp() so take a look at your override of the application class first, you may find the ON_COMMAND handler there.
I had an class that extends CWinApp, so overwriting the OnHelp function worked this way:
In the header:
class MyApp : public CWinApp
{
public:
afx_msg void OnHelp();
}
In the cpp file:
BEGIN_MESSAGE_MAP(MyApp, CWinApp)
ON_COMMAND(ID_HELP, MyApp::OnHelp)
END_MESSAGE_MAP()
void MyApp::OnHelp()
{
// your own help function
}
Since I don't know exactly what part of it alone that triggers the error, I'm not entirely sure how to better label it.
This question is a by-product of the SO question c# code seems to get optimized in an invalid way such that an object value becomes null, which I attempted to help Gary with yesterday evening. He was the one that found out that there was a problem, I've just reduced the problem to a simpler project, and want verification before I go further with it, hence this question here.
I'll post a note on Microsoft Connect if others can verify that they too get this problem, and of course I hope that either Jon, Mads or Eric will take a look at it as well :)
It involves:
3 projects, 2 of which are class libraries, one of which is a console program (this last one isn't needed to reproduce the problem, but just executing this shows the problem, whereas you need to use reflector and look at the compiled code if you don't add it)
Incomplete references and type inference
Generics
The code is available here: code repository.
I'll post a description below of how to make the projects if you rather want to get your hands dirty.
The problem exhibits itself by producing an invalid cast in a method call, before returning a simple generic list, casting it to something strange before returning it. The original code ended up with a cast to a boolean, yes, a boolean. The compiler added a cast from a List<SomeEntityObject> to a boolean, before returning the result, and the method signature said that it would return a List<SomeEntityObject>. This in turn leads to odd problems at runtime, everything from the result of the method call being considered "optimized away" (the original question), or a crash with either BadImageFormatException or InvalidProgramException or one of the similar exceptions.
During my work to reproduce this, I've seen a cast to void[], and the current version of my code now casts to a TypedReference. In one case, Reflector crashes so most likely the code was beyond hope in that case. Your mileage might vary.
Here's what to do to reproduce it:
Note: There is likely that there are more minimal forms that will reproduce the problem, but moving all the code to just one project made it go away. Removing the generics from the classes also makes the problem go away. The code below reproduces the problem each time for me, so I'm leaving it as is.
I apologize for the escaped html characters in the code below, this is Markdown playing a trick on me, if anyone knows how I can rectify it, please let me know, or just edit the question
Create a new Visual Studio 2010 solution containing a console application, for .NET 4.0
Add two new projects, both class libraries, also .NET 4.0 (I'm going to assume they're named ClassLibrary1 and ClassLibrary2)
Adjust all the projects to use the full .NET 4.0 runtime, not just the client profile
Add a reference in the console project to ClassLibrary2
Add a reference in ClassLibrary2 to ClassLibrary 1
Remove the two Class1.cs files that was added by default to the class libraries
In ClassLibrary1, add a reference to System.Runtime.Caching
Add a new file to ClassLibrary1, call it DummyCache.cs, and paste in the following code:
using System;
using System.Collections.Generic;
using System.Runtime.Caching;
namespace ClassLibrary1
{
public class DummyCache<TModel> where TModel : new()
{
public void TriggerMethod<T>()
{
}
// Try commenting this out, note that it is never called!
public void TriggerMethod<T>(T value, CacheItemPolicy policy)
{
}
public CacheItemPolicy GetDefaultCacheItemPolicy()
{
return null;
}
public CacheItemPolicy GetDefaultCacheItemPolicy(IEnumerable<string> dependentKeys, bool createInsertDependency = false)
{
return null;
}
}
}
Add a new file to ClassLibrary2, call it Dummy.cs and paste in the following code:
using System;
using System.Collections.Generic;
using ClassLibrary1;
namespace ClassLibrary2
{
public class Dummy
{
private DummyCache<Dummy> Cache { get; set; }
public void TryCommentingMeOut()
{
Cache.TriggerMethod<Dummy>();
}
public List<Dummy> GetDummies()
{
var policy = Cache.GetDefaultCacheItemPolicy();
return new List<Dummy>();
}
}
}
Paste in the following code in Program.cs in the console project:
using System;
using System.Collections.Generic;
using ClassLibrary2;
namespace ConsoleApplication23
{
class Program
{
static void Main(string[] args)
{
Dummy dummy = new Dummy();
// This will crash with InvalidProgramException
// or BadImageFormatException, or a similar exception
List<Dummy> dummies = dummy.GetDummies();
}
}
}
Build, and ensure there are no compiler errors
Now try running the program. This should crash with one of the more horrible exceptions. I've seen both InvalidProgramException and BadImageFormatException, depending on what the cast ended up as
Look at the generated code of Dummy.GetDummies in Reflector. The source code looks like this:
public List<Dummy> GetDummies()
{
var policy = Cache.GetDefaultCacheItemPolicy();
return new List<Dummy>();
}
however reflector says (for me, it might differ in which cast it chose for you, and in one case Reflector even crashed):
public List<Dummy> GetDummies()
{
List<Dummy> policy = (List<Dummy>)this.Cache.GetDefaultCacheItemPolicy();
TypedReference CS$1$0000 = (TypedReference) new List<Dummy>();
return (List<Dummy>) CS$1$0000;
}
Now, here's a couple of odd things, the above crash/invalid code aside:
Library2, which has Dummy.GetDummies, performs a call to get the default cache policy on the class from Library1. It uses type inference var policy = ..., and the result is an CacheItemPolicy object (null in the code, but type is important).
However, ClassLibrary2 does not have a reference to System.Runtime.Caching, so it should not compile.
And indeed, if you comment out the method in Dummy that is named TryCommentingMeOut, you get:
The type 'System.Runtime.Caching.CacheItemPolicy' is defined in an assembly that is not referenced. You must add a reference to assembly 'System.Runtime.Caching, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a'.
Why having this method present makes the compiler happy I don't know, and I don't even know if this is linked to the current problem or not. Perhaps it is a second bug.
There is a similar method in DummyCache, if you restore the method in Dummy, so that the code again compiles, and then comment out the method in DummyCache that has the "Try commenting this out" comment above it, you get the same compiler error
OK, I downloaded your code and can confirm the problem as described.
I have not done any extensive tinkering with this, but when I run & reflector a Release build all seems OK (= null ref exception and clean disassembly).
Reflector (6.10.11) crashed on the Debug builds.
One more experiment: I wondered about the use of CacheItemPolicies so I replaced it with my own MyCacheItemPolicy (in a 3rd classlib) and the same BadImageFormat exception pops up.
The exception mentions : {"Bad binary signature. (Exception from HRESULT: 0x80131192)"}