![String Example
The String class
Is an immutable class
Uses an indexer (get accessor but no set accessor)
class String
{
public char this[int index]
{
get {
if (index < 0 || index >= Length)
throw new IndexOutOfRangeException( );
...
}
}
...
}](https://image.slidesharecdn.com/14propertiesandindexers-190506070244/85/Module-14-properties-and-indexers-15-320.jpg)
![BitArray Example
class BitArray
{
public bool this[int index]
{
get {
BoundsCheck(index);
return (bits[index >> 5] & (1 << index)) != 0;
}
set {
BoundsCheck(index);
if (value) {
bits[index >> 5] |= (1 << index);
} else {
bits[index >> 5] &= ~(1 << index);
}
}
}
private int[ ] bits;
}](https://image.slidesharecdn.com/14propertiesandindexers-190506070244/85/Module-14-properties-and-indexers-16-320.jpg)
Module 14 properties and indexers
- 2. Overview Using Properties Using Indexers
- 3. Using Properties Why Use Properties? Using Accessors Comparing Properties to Fields Comparing Properties to Methods Property Types Property Example
- 4. Why Use Properties? Properties provide: A useful way to encapsulate information inside a class Concise syntax Flexibility
- 5. Using Accessors Properties provide field-like access Use get accessor statements to provide read access Use set accessor statements to provide write access class Button { public string Caption // Property { get { return caption; } set { caption = value; } } private string caption; // Field }
- 6. Comparing Properties to Fields Properties are “logical fields” The get accessor can return a computed value Similarities Syntax for creation and use is the same Differences Properties are not values; they have no address Properties cannot be used as ref or out parameters to methods
- 7. Comparing Properties to Methods Similarities Both contain code to be executed Both can be used to hide implementation details Both can be virtual, abstract, or override Differences Syntactic – properties do not use parentheses Semantic – properties cannot be void or take arbitrary parameters
- 8. Property Types Read/write properties Have both get and set accessors Read-only properties Have get accessor only Are not constants Write-only properties – very limited use Have set accessor only Static properties Apply to the class and can access only static data
- 9. Property Example public class Console { public static TextReader In { get { if (reader == null) { reader = new StreamReader(...); } return reader; } } ... private static TextReader reader = null; }
- 10. Using Indexers What Is an Indexer? Comparing Indexers to Arrays Comparing Indexers to Properties Using Parameters to Define Indexers String Example BitArray Example
- 11. What Is an Indexer? An indexer provides array-like access to an object Useful if a property can have multiple values To define an indexer Create a property called this Specify the index type To use an indexer Use array notation to read or write the indexed property
- 12. Comparing Indexers to Arrays Similarities Both use array notation Differences Indexers can use non-integer subscripts Indexers can be overloaded—you can define several indexers, each using a different index type Indexers are not variables, so they do not denote storage locations—you cannot pass an indexer as a ref or an out parameter
- 13. Comparing Indexers to Properties Similarities Both use get and set accessors Neither have an address Neither can be void Differences Indexers can be overloaded Indexers cannot be static
- 14. Using Parameters to Define Indexers When defining indexers Specify at least one indexer parameter Specify a value for each parameter you specify Do not use ref or out parameter modifiers
- 15. String Example The String class Is an immutable class Uses an indexer (get accessor but no set accessor) class String { public char this[int index] { get { if (index < 0 || index >= Length) throw new IndexOutOfRangeException( ); ... } } ... }
- 16. BitArray Example class BitArray { public bool this[int index] { get { BoundsCheck(index); return (bits[index >> 5] & (1 << index)) != 0; } set { BoundsCheck(index); if (value) { bits[index >> 5] |= (1 << index); } else { bits[index >> 5] &= ~(1 << index); } } } private int[ ] bits; }
- 17. Review Using Properties Using Indexers