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CA1864: Prefer the 'IDictionary.TryAdd(TKey, TValue)' method
Learn about code analyzer rule CA1864 - Prefer the 'IDictionary.TryAdd(TKey, TValue)' method
06/30/2023
CA1864
PreferDictionaryTryMethodsOverContainsKeyGuardAnalyzer
CA1864
CSharp
VB

CA1864: Prefer the 'IDictionary.TryAdd(TKey, TValue)' method

Property Value
Rule ID CA1864
Title Prefer the 'IDictionary.TryAdd(TKey, TValue)' method
Category Performance
Fix is breaking or non-breaking Non-breaking
Enabled by default in .NET 8 As suggestion

Cause

xref:System.Collections.Generic.Dictionary%602.Add%2A?displayProperty=nameWithType is guarded by a xref:System.Collections.Generic.Dictionary%602.ContainsKey(%600)?displayProperty=nameWithType call.

Rule description

Both xref:System.Collections.Generic.Dictionary%602.ContainsKey(%600)?displayProperty=nameWithType and xref:System.Collections.Generic.Dictionary%602.Add%2A?displayProperty=nameWithType perform a lookup, which is redundant. xref:System.Collections.Generic.Dictionary%602.Add%2A?displayProperty=nameWithType also throws an exception if the key is already present in the dictionary. It's more efficient to call xref:System.Collections.Generic.Dictionary%602.TryAdd%2A?displayProperty=nameWithType, which returns a Boolean value that indicates if the value was added or not. TryAdd doesn't overwrite the key's value if the key is already present.

How to fix violations

Replace a call to xref:System.Collections.Generic.Dictionary%602.ContainsKey(%600)?displayProperty=nameWithType that's followed by a call to xref:System.Collections.Generic.Dictionary%602.Add%2A?displayProperty=nameWithType with a single call to xref:System.Collections.Generic.Dictionary%602.TryAdd%2A?displayProperty=nameWithType.

Example

The following code snippet shows a violation of CA1864:

void Run(IDictionary<int, string> dictionary)
{
    if(!dictionary.ContainsKey(2)) {
        dictionary.Add(2, "Hello World");
    }
}
Sub Run(dictionary As IDictionary(Of Integer, String))
    If Not dictionary.ContainsKey(2) Then
        dictionary.Add(2, "Hello World")
    End If
End Sub

The following code snippet fixes the violation:

void Run(IDictionary<int, string> dictionary)
{
    dictionary.TryAdd(2, "Hello World");
}
Sub Run(dictionary As IDictionary(Of Integer, String))
    dictionary.TryAdd(2, "Hello World")
End Sub

When to suppress warnings

It's safe to suppress this warning if performance isn't a concern and if you handle the exception that might be thrown by xref:System.Collections.Generic.Dictionary%602.Add%2A?displayProperty=nameWithType.

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 CA1864
// The code that's violating the rule is on this line.
#pragma warning restore CA1864

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

[*.{cs,vb}]
dotnet_diagnostic.CA1864.severity = none

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