CA1854: Prefer the IDictionary.TryGetValue(TKey, out TValue) method

Property	Value
Rule ID	CA1854
Title	Prefer the IDictionary.TryGetValue(TKey, out TValue) method
Category	Performance
Fix is breaking or non-breaking	Non-breaking
Enabled by default in .NET 10	As suggestion

Cause

An IDictionary element access that's guarded by an IDictionary.ContainsKey check.

Rule description

When an element of an IDictionary is accessed, the indexer implementation checks for a null value by calling the IDictionary.ContainsKey method. If you also call IDictionary.ContainsKey in an if clause to guard a value lookup, two lookups are performed when only one is needed.

How to fix violations

Replace the IDictionary.ContainsKey invocation and element access with a call to the IDictionary.TryGetValue method.

Violation:

public string? GetValue(string key)
{
    if (_dictionary.ContainsKey(key))
    {
        return _dictionary[key];
    }

    return null;
}

Public Function GetValue(key As String) As String
    If _dictionary.ContainsKey(key) Then
        Return _dictionary(key)
    End If

    Return Nothing
End Function

Fix:

public string? GetValue(string key)
{
    if (_dictionary.TryGetValue(key, out string? value))
    {
        return value;
    }

    return null;
}

Public Function GetValue(key As String) As String
    Dim value as String

    If _dictionary.TryGetValue(key, value) Then
        Return value
    End If

    Return Nothing
End Function

When to suppress warnings

It's safe to suppress this warning if you're using a custom implementation of IDictionary that avoids a value lookup when performing the IDictionary.ContainsKey check.

Suppress a warning

If you just want to suppress a single violation, add preprocessor directives to your source file to disable and then re-enable the rule.

#pragma warning disable CA1854
// The code that's violating the rule is on this line.
#pragma warning restore CA1854

To disable the rule for a file, folder, or project, set its severity to none in the configuration file.

[*.{cs,vb}]
dotnet_diagnostic.CA1854.severity = none

For more information, see How to suppress code analysis warnings.