- Understanding the Role of XAP Files
- The Windows Phone Capabilities Model
- The Threading Model for XAML-Based Graphics and Animation in Windows Phone
- Understanding the Frame Rate Counter
- The Windows Phone Application Analysis Tool
- Reading Device Information
- Applying the Model-View-ViewModel Pattern to a Windows Phone App
- Property Change Notification
- Using Commands
- Argument Validation
- A Platform-Agnostic Dialog Service
- Consuming Local Web Applications
- Summary
This chapter is from the book
This chapter is from the book
This chapter is from the book
Argument Validation
The book sample code commonly uses a custom ArgumentValidator class to ensure that method arguments are not null or fall within a valid range. This allows a method to fail fast, rather than continuing and raising a more difficult to diagnose error.
You frequently see statements like the following at the beginning of a method:
stringPerformSomeAction(stringvalue) { stringField =ArgumentValidator.AssertNotNull(value,"value"); ... }
Here, if value is null, then an ArgumentNullException is thrown. If not null, then the stringField field is set to the value in a fluent manner.
All the ArgumentValidator methods are fluent; they return the value passed to them so that they can be assigned to local variables or fields in a single statement.
The ArgumentValidator.AssertNotNull method is as follows:
publicstaticT AssertNotNull<T>(T value,stringparameterName)whereT :class{if(value ==null) {thrownewArgumentNullException(parameterName); }returnvalue; }
ArgumentValidator contains various other assertion methods for strings and numeric values. Some are briefly discussed.
ArgumentValidator allows you to assert that an argument falls within a particular range. The following AssertLessThan method ensures that the value is less than a certain value:
publicstaticdoubleAssertLessThan(doublecomparisonValue,doublevalue,stringparameterName) {if(value >= comparisonValue) {thrownewArgumentOutOfRangeException("Parameter should be less than "+ comparisonValue, parameterName); }returnvalue; }
This then allows you to validate that a numeric value is less than, for example, 1:
ArgumentValidator.AssertLessThan(1,value,"value");
Other methods, such as AssertNotNullAndOfType, allow you to raise an exception if an argument is null or not of the expected type, and AssertNotNullOrWhiteSpace accepts a string and raises an ArgumentException if string.IsNullOrWhiteSpace(value) returns true.