We have a WebForms Control which requires that the ID of another Control implementing ITextControl is provided.
What exception should we throw if there is no control with that ID or a control is found but it's not implementing the interface?
var text = Page.FindControl(TextProviderId) as ITextControl;
if (text == null) {
throw new WhatEverException(...);
...
Should we split it into two cases and throw one exception if there is no control with that ID, and another one if said control does not implement ITextControl? If so, which exceptions should we use then?
If the control should really be there, I would say that your web form is in an invalid state if it is missing, so I would probably go for InvalidOperationException:
The exception that is thrown when a method call is invalid for the object's current state.
This would be applicable to both scenarios; regardless of whether the control is missing or if it does not implement the expected interface, the containing object is in an invalid state.
If this is a scenario that is expected to happen for various reasons (let's say that you are making some tool that others will program against, and this is a situation that they might very well produce), perhaps you should instead create two custom exceptions that make it very clear what is happening and how to correct it (such as ControlNotFoundException and InterfaceNotFoundException or something similar).
ArgumentOutOfRangeException?
Whether or not you should split them up into different exceptions probably depends most on whether or not you think it is likely that anyone will ever want to distinguish the two exceptions in different catch blocks.
Not knowing exactly how this will be used, this seems like the kind of error that should be brought to the developer's attention, where rewriting code to point to the correct file or implement the correct interface is the proper action, rather than implementing a try-catch and give the user friendly error messages. As such, I'd just throw an ArgumentException.
Related
Is that a good practice to throw exception from controller?
For instance we may throw IllegalStateException from some controller's method if Request hasn't some attribute.
Also for instance we may throw IllegalArgumentException from some controller's method if Request's parameter is not in appropriate format/range.
No, I don't think so. Who will handle it? The client. What does handling it mean? Exceptions won't tell them what to do. Better to change the UI to instruct them on what do to next. You see this in every decent web UI that you use: the text box is highlighted and you're told what the proper range is. What kind of experience would seeing a stack trace be?
So the controller should catch all exceptions and change the display accordingly.
I don't think it is a good idea to throw such exception to end user. Instead you may alert end user a meaningful error message which use can easily understand what is wrong.
I am using asp.net MVC3 and I am very new to this technology.
My models are designed in such a way that the properties will throw validation errors if the data is invalid. In this case, the properties are not set with invalid data.
When I redisplay my editing-view, validation error messages are shown; however the values that the user previously entered are gone because the model that it is bound to only contains the old-valid data.
For example, say I had a Person class and the Name property cannot be a null or empty string otherwise it throws a validation exception and prevents the property from being set. Now say the user removes the value from the Name property and tries to save the Person from the web. A validation exception will be thrown and handled properly to add the error to the ModelState so that it is displayed on the screen; however the old value for the Name is redisplayed since the invalid, empty string never made it into the property.
I do not know how to solve this problem and any advice on the issue would be greatly appreciated.
My advise is allow invalid data but use validation attributes. You wont save invalid entities so there is no problem and this is the standard approach these days. If you don't want do that, there is no easy solution. Most simple solution would be using the info from Request.Form
You should implement IValidatableObject to performe this kind of validation at server side.
From MSDN IValidatableObject Interface:
Provides a way for an object to be invalidated.
Theres an exemple here Using IValidatableObject Custom Validation, also from MSDN.
The solution to this problem was to create a ViewModel that allowed invalid data to be entered into this. This solution also simplified my ModelBinder classes because it took on most of the work.
Currently in the ASP.NET application I'm developing, basic validations (ie required fields) are being done in the Presentation Layer, using Validators and a ValidationSummary. This is working great for me specifically since the ValidationSummary will display multiple error messages (assuming multiple Validators are set to invalid).
I also have some validations being done in the business layer - due to their complexity (and data service layer reliance) I'd rather not keep them in the presentation layer. However, I'm not sure the best way to send these back to the presentation layer for display to the user. My initial consideration is to send back a List<string> with failed validation messages and then dynamically create a CustomValidator control (since apparently you can only bind one error message to one Validator control) for each error to show in the ValidationSummary when there are any.
I'm assuming I'm not the first one to come across this issue, so I'm wondering if anyone has any suggestions on this.
Thanks!
There are essentially two ways to do this: either by passing back an error code/object from your business layer, or throw out an exception. You can also combine both.
For an example, you can take a look SqlException class. When you send a SQL to SQL Server, it runs a query parser to parse your SQL first. If it sees syntax error, then it will throw out a SqlException and terminate the query. There may be multiple syntax errors in your query. So SqlExeption class has an Errors property that contains a list of errors. You can then enumerate through that list in your presentation layer to format your error message, probably with a CustomValidator.
You can also simply just return the error list without throwing an exception. For example, you can have your function to return a List in case at least one error occurred and return null in case the call was successful. Or you can pass List as an argument into your function. They are all fine, it all depends on which way you feel is more convenient. The advantage of throwing out an exception is it unwinds multiple call frames immediately, so you don’t have to check return value on every level. For example, if function A calls function B , B calls function C, C sees something wrong, then if let C to return an error object (or error code), then B has to have code to check whether C returned an error and pass that error code/value back, A have to check it as well ---- you need to check it on every level. On the other hand, if you just let C to throw an exception, then the code goes straight to the exception handler. You don’t have check return values on every level.
Suppose I have a button in an aspx page that performs a save of the form data to the database. In the associated event handler, before sending the updates, I read something from a webservice, operation that might result in an exception. In case of an error I want to have an adequate message displayed on the page, and all the data in the form preserved. How can I achieve this? Also, all my pages inherit from a basepage, so I would like, if possible to have all the error handling code in the base class. I do not want, if possible, to surround any web service call with try-catch blocks, I would in case of any unhandled exception to call some method automatically, something like Page_error, but still preserve the data in my forms.
You can easily put a method that manages the display message (maybe setting the text of some errorMessageLabel) in a superclass called from any derived class (if you wanna use inheritance to setup a template for your pages) if an exception is thrown (you can put the call to the superclas method in a catch block if there's actually an exception being thrown or you can manage this manually if the webservice is unavailable depending on your programming style).
As far as preserving the data presented, if viewstate is on and you are not populating your page dynamically then you're ok - if not, you need to explicitly save state information in viewState or session entries and retrieve them back if something goes wrong.
This bit really depends on how your page is actually implemented.
I am using methods with the Attribute [WebMethod] in my aspx pages. I don't use any asp.net ajax but jQuery to call these methods and return objects in JSON. This all works fine.
Next I added an authorization check inside the webMethod, if the current user doesn't have access to the feature I need to let the calling JavaScript know.
So I am throwing an AccessViolationException exception which can then be parsed by the OnError callback function in JavaScript. This works too but the exception includes the full StackTrace and I don't want to make this available to the calling client.
What other ways I could use to return an "Access Denied" to the client when the WebMethod returns a business object?
I'm using ASP.Net 3.5SP1 and jQuery 1.32
You can also add a:
customErrors mode="On"/
in your web.config, this will cut away the stack trace and leave you only the exception message
Why propagate errors through the wire? why not use an error response ?
Just wrap your object in a response object wich can contain an error code for status and an error message to present to users.
As suggested by NunFur I changed my approach and rather than throwing an error, I return a 'richer' object.
There are at least two options, the first one would be to encapsulate my business object into a response object with some status properties. I tried this but it makes the JSON more complicated.
So rather than adding a new object I added two properties to my business object, something like ServiceStatus and ServiceMessage. By default these are 200 and '', but can be set by the WebMethod code if anything goes wrong (no access, proper error). In this case they business object will be 'empty' (no data). The JavaScript code then first checks for the ServiceStatus and reacts appropriately.
I add the two fields to all my objects that are returned by WebMethods, even a simple string. They have to implement an Interface with those two properties.
Now I have complete control over that goes over the wire in case something unexpected is happening.
Thanks for the input
I save exceptions for when things go really wrong. (e.g. can't connect to the database)
Either return nothing (null/nill/whatever), or return a false bool value.
Sorry that I don't have a better answer than that...I'll have to keep looking myself.
You could look at SoapException: http://msdn.microsoft.com/en-us/library/system.web.services.protocols.soapexception(VS.71).aspx
I'm just not sure, if it will work when it is called from JavaScript. Espeially if it's called with a get-request.
BTW AccessViolationException is to my best knowlegde ment to be thrown when the application is accessing memory it has no access to.
/Asger