OC lesson 6

Main content: Block (Block syntax, Block usage, and Block implement array sorting)

Main content: Block (Block syntax, Block usage, and Block implement array sorting)

I. Block syntax

Block: Block syntax, essentially an anonymous function (a function without a function name), similar to a function pointer

Function review:

Implements the encapsulation of a function code block (three steps: function declaration, function definition, and function call)

Function pointer review:

Function pointer (variable): The pointer variable that stores the function address (function name)

Int (* p) (int x, int y) = sum

Function pointer type: int (*) (int x, int y), that is, pointer to two integer parameters, an integer return value function

Function pointer variable: p; function pointer value: sum

Block:

Note:

1. the last ";" must be written.

2. the parameter variable name cannot be omitted.

3. the block value is an anonymous function.

Anonymous function: a function without a name

Block syntax:

Details:

Block type: int (^) int

Block variable: myblock

Block value: ^ (int sum) {return 7 * sum ;};

That is: ^ return value type (parameter list) {function body} (the return value type can be omitted)

II. Block Usage

Example:

Write a Block that returns two integer values and

Int (^ sum) (int, int) = ^ (int x, int y ){

Return x + y;

}

Int a = sum (20, 10); // call the block function

Write a block that calculates the maximum value.

Int (^ maxBlock) (int, int) = ^ (int x, int y ){

Return x> y? X: y;

}

Perform typedef on the block

Typedef int (^ sumBlock) (int x, int y );

New type: sumBlock

Original type: int (^) (int, int)

Equivalent: sumBlock ^ sum2 = ^ (int x, int y ){

Return x + y;

}

3. block and local variables and global variables

External variables can be used inside the block.

For global variables: readable and writable

For local variables: readable and non-writable. if you want to change the value of a local variable, add _ block before the local variable for modification.

Example:

Block and local variables

Block and global variables:

III. Block and array sorting

Example:

Sort Student objects

Student * stu1 = [Student StudentWithName: @ "xiaoming", age: 21];

Student * stu2 = [Student StudentWithName: @ "", age:];

NSMutableArray * mu = [NSMutableArray arrayWithObjects: stu1, stu2, nil];

Mu sortUsingcomparator: ^ NSComparionResult (id obj1, id obj2 ){

If ([obj1 getAge]> [obj2 getAge]) {

Return NSOrderedDescending;

} Else if ([obj1 getAge] <[obj2 getAge]) {

Return NSOrderedAscending;

} Else {

Return NSOrderedSame;

}

}

IV. literal

Literal is a new writing method that can simplify the code to a certain extent.

Note: objects created literally are constructed by variables and are immutable.