Cast() vs. OfType() in LINQ: When Should I Use Each for Type Conversion?

Type conversion in LINQ: Detailed explanation of Cast() and OfType() methods

LINQ (Language Integrated Query) is a powerful tool in the .NET framework that allows developers to query and transform data using familiar syntax. When you need to convert elements in ArrayList to IEnumerable, there are two main methods: Cast() and OfType().

Cast() method

The Cast() method is used to explicitly convert all elements in the ArrayList to the specified type. It attempts to cast each element to the target type, regardless of its actual type. If any element fails to be cast, an InvalidCastException is thrown.

OfType() method

OfType() method selectively converts only those elements that can be safely converted to the target type. It returns an IEnumerable containing only elements matching the specified type. Any elements that cannot be converted will be excluded from the result set.

Applicable scenarios for Cast() and OfType() methods

Choosing Cast() or OfType() depends on your specific needs:

• Using Cast():

  • You are sure that all elements in the ArrayList can be successfully converted to the target type.
  • You want to treat every element as the target type, even if its actual type is different.

• Using OfType():

  • You expect that there may be some elements in the ArrayList that cannot be converted to the target type.
  • You only want to deal with elements that can be safely converted.

Example

Suppose you have an ArrayList containing strings and integers:

<code class="language-csharp">object[] objs = new object[] { "12345", 12 };</code>

• Use Cast():

  <code class="language-csharp">  try
    {
        string[] strArr = objs.Cast<string>().ToArray();
    }
    catch (InvalidCastException)
    {
        // 处理异常
    }</code>

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  In this case, Cast() will try to convert both elements to strings. Since one of them is an integer, an InvalidCastException is thrown.

• Use OfType():

  <code class="language-csharp">  string[] strArr = objs.OfType<string>().ToArray(); // 只包含 "12345"</code>

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  OfType() will successfully retrieve string elements from the ArrayList and exclude integer elements.

By understanding the difference between Cast() and OfType(), you can effectively convert types and filter data when using LINQ, ensuring the accuracy and reliability of queries.

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