Cocoa：NSValue

Cocoa：NSValue

An NSValue object is a simple container for a single C or Objective-C data item. It can hold any of the scalar types such as int, float, and char, as well as pointers, structures, and object ids. The purpose of this class is to allow items of such data types to be added to collections such as instances of NSArray and NSSet, which require their elements to be objects. NSValue objects are always immutable.

Adopted Protocols

NSCoding

• encodeWithCoder:

• initWithCoder:

NSCopying

• – copyWithZone:

Tasks

Creating an NSValue

• – initWithBytes:objCType:
• + valueWithBytes:objCType:
• + value:withObjCType:
• + valueWithNonretainedObject:
• + valueWithPointer:
• + valueWithPoint:
• + valueWithRange:
• + valueWithRect:
• + valueWithSize:

Accessing Data

• – getValue:
• – nonretainedObjectValue
• – objCType
• – pointValue
• – pointerValue
• – rangeValue
• – rectValue
• – sizeValue

Comparing Objects

• – isEqualToValue:

getValue:

Copies the receiver’s value into a given buffer.

- (void)getValue:(void *) buffer

Parameters

buffer

A buffer into which to copy the receiver's value. buffer must be large enough to hold the value.

isEqualToValue:

Returns a Boolean value that indicates whether the receiver and another value are equal.

- (BOOL)isEqualToValue:(NSValue *) value

Parameters

aValue

The value with which to compare the receiver.

Return Value

YES if the receiver and aValue are equal, otherwise NO. For NSValue objects, the class, type, and contents are compared to determine equality.

pointerValue

Returns the receiver's value as a pointer to void.

- (void *)pointerValue

Return Value

The receiver's value as a pointer to void. If the receiver was not created to hold a pointer-sized data item, the result is undefined.

pointValue

Returns an NSPoint structure representation of the receiver.

- (NSPoint)pointValue

Return Value

An NSPoint structure representation of the receiver.

rangeValue

Returns an NSRange structure representation of the receiver.

- (NSRange)rangeValue

Return Value

An NSRange structure representation of the receiver.

rectValue

Returns an NSRect structure representation of the receiver.

- (NSRect)rectValue

Return Value

An NSRect structure representation of the receiver.

sizeValue

Returns an NSSize structure representation of the receiver.

- (NSSize)sizeValue

Return Value

An NSSize structure representation of the receiver.

valueWithPointer:

Creates and returns an NSValue object that contains a given pointer.

+ (NSValue *)valueWithPointer:(const void *) aPointer

Parameters

aPointer

The value for the new object.

Return Value

A new NSValue object that contains aPointer.

Discussion

This method is equivalent to invoking value:withObjCType: in this manner:

NSValue *theValue = [NSValue value:&aPointer withObjCType:@encode(void *)];

This method does not copy the contents of aPointer, so you must not to deallocate the memory at the pointer destination while the NSValue object exists. NSData objects may be more suited for arbitrary pointers than NSValue objects.

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