This is maybe something I know how to do or have already done it in the past. For some reason I am drawing a blank on how to wrap my head around it. This is more for learning as well as trying to implement something in my app.
I am using a set of third party controls. These controls offer a lot of functionality which is great. However, I want to be able to create a custom object that handle the logic/properties for the datasource of this control.
For example, there is a spreadsheet like object that I am using. You supply the spreadsheet like object some data and it pulls in your data. The problem here is that you need to set the columns, their data types, and other formatting/events as well as some logic to spit the data back to the user.
List<CustomClassWithProperties> dataSource
The custom class has some properties that will be translated to the columns. Like ProductName, Price, SalesDepartment, DatePurchased etc. This can be done by supplying the spreadsheet the columns and their data types each time. I want to be able to create a helper class that you just supply a list, a visible column list, and an editable column list and the data will fill in without any other issues.
Using the above list, I would imagine something similar to this:
DataHelperClass dtHlpr = new DataHelperClass(List<CustomClassWithProperties> data, List<string> visibleColumns, List<string> editableColumns)
This data helper class will take the data input list as the spreadsheet data source. It would then take the visibleColumns list and use that to set the visible rows, same for editableColumns.
Where I am running into a mental block (long week) is when I want to be able to reuse this. Let's say I have a List that has completely different properties. I would want my constructor for the data helper to be able to handle any List I send to it. Looking at whatever code I can get to for the third party controls, it appears that their data source is of type object.
Could someone point me in the right direction? I am thinking it has to do with generics and some interface implementation. I just honestly cannot think of where to start.
You can make the class itself generic:
public class DataHelperClass<T>
{
public DataHelperClass(List<T> data, ...) { ... }
}
DataHelperClass<CustomClassWithProperties> dtHlpr = new DataHelperClass<CustomClassWithProperties>(List<CustomClassWithProperties> data, List<string> visibleColumns, List<string> editableColumns)
You'd then perform your reflection against typeof(T).
I'd also be tempted to use IEnumerable<T> rather than List<T> if possible, but that's a matter of preference, more or less.
This is similar to using a simple List<object>, except that it enforces that all objects in the list inherit from the same type (which might well be object), so you get some more type-checking than you otherwise would.
You mentioned interfaces, I don't see any reason here to include that (from what you've told us, at least), but you can certainly make a generic interface via the same syntax.
Related
I have a (not quite valid) CSV file that contains rows of multiple types. Any record could be one of about 6 different types and each type has a different number of properties. The first part of any row contains the timestamp and the type of record, followed by a standard CSV of the data.
Example
1456057920 PERSON, Ted Danson, 123 Fake Street, 555-123-3214, blah
1476195120 PLACE, Detroit, Michigan, 12345
1440581532 THING, Bucket, Has holes, Not a good bucket
And to make matters more complex, I need to be able to do different things with the records depending on certain criteria. So a PERSON type can be automatically inserted into a DB without user input, but a THING type would be displayed on screen for the user to review and approve before adding to DB and continuing the parse, etc.
Normally, I would use a library like CsvHelper to map the records to a type, but in this case since the types could be different, and the first part uses a space instead of comma, I dont know how to do that with a standard CSV library. So currently how I am doing it each loop is:
String split based off comma.
Split the first array item by the space.
Use a switch statement to determine the type and create the object.
Put that object into a List of type object.
Get confused as to where to go now because i now have a list of various types and will have to use yet another switch or if to determine the next parts.
I don't really know for sure if I will actually need that List but I have a feeling the user will want the ability to manually flip through records in the file.
By this point, this is starting to make for very long, confusing code, and my gut feeling tells me there has to be a cleaner way to do this. I thought maybe using Type.GetType(string) would help simplify the code some, but this seems like it might be terribly inefficient in a loop with 10k+ records and might make things even more confusing. I then thought maybe making some interfaces might help, but I'm not the greatest at using interfaces in this context and I seem to end up in about this same situation.
So what would be a more manageable way to parse this file? Are there any C# parsing libraries out there that would be able to handle something like this?
You can implement an IRecord interface that has a Timestamp property and a Process method (perhaps others as well).
Then, implement concrete types for each type of record.
Use a switch statement to determine the type and create and populate the correct concrete type.
Place each object in a List
After that you can do whatever you need. Some examples:
Loop through each item and call Process() to handle it.
Use linq .OfType<{concrete type}> to segment the list. (Warning with 10k
records, this would be slow since it would traverse the entire list for each concrete type.)
Use an overridden ToString method to give a single text representation of the IRecord
If using WPF, you can define a datatype template for each concrete type, bind an ItemsControl derivative to a collection of IRecords and your "detail" display (e.g. ListItem or separate ContentControl) will automagically display the item using the correct DataTemplate
Continuing in my comment - well that depends. What u described is actually pretty good for starters, u can of course expand it to a series of factories one for each object type - so that you move from explicit switch into searching for first factory that can parse a line. Might prove useful if u are looking to adding more object types in the future - you just add then another factory for new kind of object. Up to you if these objects should share a common interface. Interface is used generally to define a a behavior, so it doesn't seem so. Maybe you should rather just a Dictionary? You need to ask urself if you actually need strongly typed objects here? Maybe what you need is a simple class with ObjectType property and Dictionary of properties with some helper methods for easy typed properties access like GetBool, GetInt or generic Get?
I want to create a class and its properties on run time, the properties will be like Year2001, Year2002, Year2003, Year2004, Year2005... I get these property names on run-time, I get them in a list. Later I need to use this class to create a list which I need to show in the kendo grid.I surfed a lot and thought of using ExpandoObject, but was unsuccessful.
If all properties will be of the form YearX and contain some information about or related to that year, then I would strongly recommend you (if at all possible) to go with something along the lines of an IList<YearInfo> where YearInfo is some object containing the info you need for every year, including an integer property indicating what year the object corresponds to. If you require these objects to be unique you could use an IDictionary<int, YearObject> or ISet<YearObject> instead.
Reflection can be powerful, but it it comes at the price of complexity and loss of type safety/compile-time checks. Avoid when possible.
Sounds to me like you are really wanting to a grid with grouping support. Your idea of having the system create a CLASS at runtime is not going to fly. Even if it were possible, which I doubt it is, it is absolutely the wrong approach.
Like I say - have a read about Grouping / Hierarchy on Grid Controls (Kendo grid example here), and maybe have a look at OLAP cubes as well...
Although you have had some answers I would also like to suggest an alternative way of doing this which is using DataTables. This is the approach I take when I have any "Dynamic" data sets that I want to present to the grid.
This is also the approach that Telerik themselves take with one of their code samples.
here are a couple of links to show them doing this to DataTables and Dynamic Objects
Grid Binding to Data Table
Grid Binding to Dynamic Objects
Personally I find the binding to Tables easier to deal with as I am used to dealing with Data Tables.
I am writing a program that needs to read a set of records that describe the register map of a device I need to communicate with. Each record will have a handfull of fields that describe the properties of each register.
I don't really need to edit or modify the data in my VB or C# program, though I would like to be able to display the data on a grid. I would like to store the data in a CSV file, or perhaps an XML file. I need to enable users to edit the data off-line, preferably in excel.
I am considering using a DataTable or a Collection of "Register" objects (which I would define).
I prototyped a DataTable, and found I can read/write XML easily using the built in methods and I can easily bind to a DataGridView. I was not able to find a way to retreive info on a single register without using a query that returns a collection of rows, even though I defined a unique primaty key column. The syntax to get a value from a column is also complex, though I could be missing something on both counts.
I'm tempted to use a collection of "Register" objects that I can access via a unique key. It would be a little more coding up front, but seems like a cleaner solution overall. I should still be able to use LINQ to dataset to query subsets of registers when I need them, but would also be able to grab a single field using a the key value, something like this: Registers(keyValue).fieldName).
Which would be a cleaner approach to the problem?
Is there a way to read/write XML into a Collection without needing custom code?
Could this be accomplished using String for a key?
UPDATE: Sounds like the consensus is towards the Collection of register Objects. Makes sense to me. I was leaning that way, and since nobody pointed out any DataTable features that would simplify acessing a single row, it looks like the Collection is clearly the way to go. Thanks to those who weighed in.
I would be inclined not to use data sets. It would be better to work with objects and collections. Your code will be more maintainable/readable, composable, testable & reusable.
Given that you can do queries on the data set to return particular row, you might find that a LINQ query to turn the rows into objects may be all the custom code that you need.
Using a Dictionary<string, Register> for look ups is a good idea if you have a large number of items (say greater than 1000). Otherwise a simple LINQ query should be fine.
It depends on how you define 'clean'.
A generic collection is potentially MUCH more lightweight than a DataTable. But on the other hand that doesn't seem to be too much of an issue for you. And unless you go into heavy reflection you'll have to write some code to read/write xml.
If you use a key I'd also recommend (in the case of the collection) to use a Dictionary. That way you have a Collection of the raw data and still can identify each entry through the key in the Dictionary.
I usually use datatables if its something quick and unlikely to be used in any other way. If it's something I can see evolving into an object that has its own use within the app (like your Register Object you mentioned).
It might be a little extra code up front - but it saves converting from a datatable to the collection in the future if you come up with something you would like to do based on an individual row, or if you want/need to add some sort of extra functionality to that element down the road.
I would go with the collection of objects so you can swap out the data access later if you need to.
You can serialize classes with an xml serializer and defining a Serialize attribute or something like that (it has been a while since I done that, sorry for the vagueness). A DataSet or DataTable works great with XML.
Both DS and DT have ReadXml and WriteXml methods. XML must be predefined format, but it works seamlessly.
Otherwise, I personally like collections or dictionaries; DS/DT are OK, but I like custom objects, and LINQ adds in some power.
HTH.
i´m trying to query a DataTable object without specifying the fields, like this :
var linqdata = from ItemA in ItemData.AsEnumerable()
select ItemA
but the returning type is
System.Data.EnumerableRowCollection<System.Data.DataRow>
and I need the following returning type
System.Data.EnumerableRowCollection<<object,object>>
(like the standard anonymous type)
Any idea?
Thanks
If I understand you correctly, you'd like to get a collection of objects that you don't need to define in your code but that are usable in a strongly typed fashion. Sadly, no you can't.
An anonymous type seems like some kind of variant or dynamic object, but it is in fact a strongly typed class that is defined at compile time. .NET defines the type for you automatically behind the scenes. In order for .net to be able to do this, it has to have some clue from the code with which to infer the type definition. It has to have something like:
from ItemA in ItemData.AsEnumerable()
select ItemA.Item("Name"), ItemA.Item("Email")
so it knows what members to define. There's no way to get around it, the information has to logically be there for the anonymous type to be defined.
Depending on why exactly your are trying to do this, there are some options.
If you want intellisense while still encapsulating your data access, you can return xml instead of a datatable from your encapsulated data access class. (You can convert data tables to xml very easily. You'll want to use the new System.Xml.Linq classes like the XElement. They're great!) Then you can use VS2008's ability to create an xsd schema from xml. Then use/import that schema at the top of your code page, and you have intellisense.
If you have to have an object an with properties for your data, but don't want to define a class/structure for them, you'll love the new dynamic objects coming in C#4.0/VB10. You have object properties based on what the sql returns, but you won't have intellisense. There is also a performance cost to this, but (a) that might not matter for your situation and (b) it actually is not so bad in some situations.
If you're just trying to avoid making a lot of classes, consider defining structs/structures on the same code file, beneath your class definition. When you add more columns to your result set, it's easy to adjust a struct with more public fields.
In short you can have any two of the following three: (a) dynamic, (b) strontly-typed objects, (3) intellisense. But not all three.
There is one way to accomplish what you want, but it required knowledge of dynamic linq. You would build the query during run-time and then use it. I am no expert and have never really played around with it, but here is a link to Scott Guthrie's blog about it - Dynamic Linq. Hope that helps.
Wade
I'm currently having a problem with a ShoppingCart for my customer.
He wants to be able to add Text between the CartItems so I was wondering if there is some way to still only have one List.
My solution would be to have two lists, one of type IList that gets iterated over when calculating Weight and overall Price of the Cart while having another IList that only exposes the necessary fields for displaying it in the ListView and that is a SuperType of CartItem. (But how do I then access additional fields for the listView, defaulting weight and price to 0 in the Description-Text-Class would break LSP).
But having two lists somehow feels a bit odd (and still gives me problems), so I was wondering if I could do some sort of a TypedList where I specify the Type of each item.
Any suggestions are welcome, I'm not really happy with both options.
Use an interface:
ICartListItem
And make your list be:
List<ICartListItem>
Now, create several types, have all of them implement this interface, and you can store them all safely in your list.
Alternatively, if you want there to be some default logic in a CartItem, use a base class instead of an interface.
You can make a class and, inside of that, define the properties of the required list type and then make a list of same class.
For example, if I wanted to make a list of strings and bools, I would make two properties in one class and then make a list of that class.
The Interface sounds like overkill. I'd just add a property to your current CartItem named something like "TextAfterItem".
Also: make sure your customer understands the cost of this feature in terms of security overhead. It sounds like they think this should be a simple update, but you're allowing users to enter text that will be displayed directly back to the page, and that's a dangerous proposition.