Using TrueForAll with Generic Lists

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If you work with generic lists, you’ll know sometimes you need to check the values in the list to see if they match certain criteria. A method I don’t see used allot is TrueForAll. This is part of the List<T> class. It determines whether every element in the List<(Of <(T>)>) matches the conditions defined by the specified predicate. For example you have the following code:

C#

var numbers = new List<int>() { 4, 6, 7, 8, 34, 33, 11};

VB.NET (Option Infer On)

Dim numbers = New List(Of Integer) (New Integer() {4, 6, 7, 8, 34, 33, 11})

If you needed to check if you had any zeros values, you could write a foreach statement like this:

C#

bool isTrue = false;
foreach (var i in numbers)
{
if (i == 0)
{
          isTrue = true;
}
}

VB.NET

Dim isTrue As Boolean = False
For Each i In numbers
If i = 0 Then
          isTrue = True
End If
Next i

There’s nothing wrong with that code, but by using the TrueForAll method, you can roll that up into one line of code:

C#

var numbers = new List<int>() { 4, 6, 7, 8, 34, 33, 11};
var isTrue = numbers.TrueForAll(o => o > 0);

VB.NET

Dim numbers = New List(Of Integer) (New Integer() {4, 6, 7, 8, 34, 33, 11})
Dim isTrue = numbers.TrueForAll(Function(o) o > 0)

That makes your code more readable than the previous example, and it also looks more elegant in my opinion.

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About The Author

Malcolm Sheridan is a Microsoft awarded MVP in ASP.NET and regular presenter at conferences and user groups throughout Australia. Being an ASP.NET Insider, his focus is on web technologies and has been for the past 10 years. He loves working with ASP.NET MVC these days and also loves getting his hands dirty with JavaScript. He also blogs regularly at DotNetCurry.com. Follow him on twitter @malcolmsheridan