移动开发之设计模式- 数据访问对象模式(IOS&Android)

资源

完全参照数据访问对象模式|菜鸟教程但不包括IOS代码

数据访问对象模式

数据访问对象模式（Data Access Object Pattern）或 DAO 模式用于把低级的数据访问 API 或操作从高级的业务服务中分离出来。以下是数据访问对象模式的参与者。

• 数据访问对象接口（Data Access Object Interface） - 该接口定义了在一个模型对象上要执行的标准操作。
• 数据访问对象实体类（Data Access Object concrete class） - 该类实现了上述的接口。该类负责从数据源获取数据，数据源可以是数据库，也可以是 xml，或者是其他的存储机制。
• 模型对象/数值对象（Model Object/Value Object） - 该对象是简单的 POJO，包含了 get/set 方法来存储通过使用 DAO 类检索到的数据。

Android

Student

public class Student {
   private String name;
   private int rollNo;
 
   Student(String name, int rollNo){
      this.name = name;
      this.rollNo = rollNo;
   }
 
   public String getName() {
      return name;
   }
 
   public void setName(String name) {
      this.name = name;
   }
 
   public int getRollNo() {
      return rollNo;
   }
 
   public void setRollNo(int rollNo) {
      this.rollNo = rollNo;
   }
}

StudentDao.java

import java.util.List;
 
public interface StudentDao {
   public List<Student> getAllStudents();
   public Student getStudent(int rollNo);
   public void updateStudent(Student student);
   public void deleteStudent(Student student);
}

StudentDaoImpl

import java.util.ArrayList;
import java.util.List;
 
public class StudentDaoImpl implements StudentDao {
   
   //列表是当作一个数据库
   List<Student> students;
 
   public StudentDaoImpl(){
      students = new ArrayList<Student>();
      Student student1 = new Student("Robert",0);
      Student student2 = new Student("John",1);
      students.add(student1);
      students.add(student2);    
   }
   @Override
   public void deleteStudent(Student student) {
      students.remove(student.getRollNo());
      System.out.println("Student: Roll No " + student.getRollNo() 
         +", deleted from database");
   }
 
   //从数据库中检索学生名单
   @Override
   public List<Student> getAllStudents() {
      return students;
   }
 
   @Override
   public Student getStudent(int rollNo) {
      return students.get(rollNo);
   }
 
   @Override
   public void updateStudent(Student student) {
      students.get(student.getRollNo()).setName(student.getName());
      System.out.println("Student: Roll No " + student.getRollNo() 
         +", updated in the database");
   }
}

DaoPatternDemo

public class DaoPatternDemo {
   public static void main(String[] args) {
      StudentDao studentDao = new StudentDaoImpl();
 
      //输出所有的学生
      for (Student student : studentDao.getAllStudents()) {
         System.out.println("Student: [RollNo : "
            +student.getRollNo()+", Name : "+student.getName()+" ]");
      }
 
 
      //更新学生
      Student student =studentDao.getAllStudents().get(0);
      student.setName("Michael");
      studentDao.updateStudent(student);
 
      //获取学生
      studentDao.getStudent(0);
      System.out.println("Student: [RollNo : "
         +student.getRollNo()+", Name : "+student.getName()+" ]");      
   }
}

结果

Student: [RollNo : 0, Name : Robert ]
Student: [RollNo : 1, Name : John ]
Student: Roll No 0, updated in the database
Student: [RollNo : 0, Name : Michael ]

IOS

Student.h

#import <Foundation/Foundation.h>

@interface Student : NSObject
@property (nonatomic, strong) NSString* name;
@property (nonatomic, assign) int rollNo;
- (instancetype)initWithName:(NSString*)name rollNo:(int)rollNo;
@end

Student.m

#import "Student.h"
@interface Student()
@end

@implementation Student
- (instancetype)initWithName:(NSString*)name rollNo:(int)rollNo
{
    self = [super init];
    if (self) {
        self.name = name;
        self.rollNo = rollNo;
    }
    return self;
}

- (NSString *)description
{
    return [NSString stringWithFormat:@"Student: [RollNo : %d , Name : %@]", self.rollNo, self.name];
}
@end

StudentDaoImpl.h

#import <Foundation/Foundation.h>
#import "Student.h"


@protocol StudentDao <NSObject>
-(NSArray*)getAllStudents;
-(Student*)getStudent:(int)rollNo;
-(void)updateStudent:(Student*)student;
-(void)deleteStudent:(Student*)student;
@end

@interface StudentDaoImpl : NSObject <StudentDao>

@end

StudentDaoImpl.m

#import "StudentDaoImpl.h"

@interface StudentDaoImpl ()
@property (nonatomic, strong) NSMutableArray *students;
@end

@implementation StudentDaoImpl

- (instancetype)init
{
    self = [super init];
    if (self) {
        self.students = [[NSMutableArray alloc]init];
        Student *student1 = [[Student alloc] initWithName:@"Robert" rollNo:0];
        Student *student2 = [[Student alloc] initWithName:@"John" rollNo:1];
        [self.students addObject:student1];
        [self.students addObject:student2];
    }
    return self;
}

- (void)deleteStudent:(Student *)student {
    [self.students removeObject:student];
    NSLog(@"Student: roll No %d , deleted from database.", student.rollNo);
}

- (NSArray *)getAllStudents {
    //self.students removeObject:
    return self.students;
}

- (Student *)getStudent:(int)rollNo {
    if(rollNo <= [self.students count]) {
        return [self.students objectAtIndex:rollNo];
    }
    return nil;
}

- (void)updateStudent:(Student *)student {
    [[self.students objectAtIndex:student.rollNo] setName:student.name];
    NSLog(@"Student: Roll No %d ,updated in the database.", student.rollNo);
}

@end

ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
    
    id<StudentDao> studentDao = StudentDaoImpl.new;
    
    //输出所有的学生
    for (Student *student in [studentDao getAllStudents]) {
        NSLog(@"%@", [student description]);
    }

    //更新学生
    Student *student = [[studentDao getAllStudents] objectAtIndex:0];
    [student setName:@"Michael"];
    [studentDao updateStudent:student];
    
    //获取学生
    NSLog(@"%@", [[studentDao getStudent:0] description]);
}

结果

 Student: [RollNo : 0 , Name : Robert]
 Student: [RollNo : 1 , Name : John]
 Student: Roll No 0 ,updated in the database.
 Student: [RollNo : 0 , Name : Michael]