使用图像

为了便于操作对象，iOS中定义了图像类：
UIImage（UIKit框架中定义的图像类）
CGImage（在Core Graphics框架（或Quartz 2D）中定义的图像类）
CIImage(Core Image)
以上三者之间可以相互转化。

创建图像的四种方式

1.从资源文件中直接加载
2.从应用程序沙盒目录加载
3.从云服务器端获取
4.从设备图片库选取或从照相机抓取

例图

Swift代码

import UIKit

let FILE_NAME = "WeChat_1468557469.png"

class ViewController: UIViewController {

    @IBOutlet weak var imageView: UIImageView!
    
    override func viewDidLoad() {
        super.viewDidLoad()
        //把资源文件中的图片复制到沙河中document目录下
        self.createEditableCopyOfDatabaseIfNeeded()
        self.imageView.image = UIImage(named:"WeChat_1468557469.png")
        
    }
    func createEditableCopyOfDatabaseIfNeeded() {
        // NSFileManager采用单例设计模式
        let fileManager = NSFileManager.defaultManager()
        let writalbeDBPath = applicationDocumentsDirectoryFile()
        let dbexits = fileManager.fileExistsAtPath(writalbeDBPath)
        //如果文件不存在，则copy一个图文到沙盒中
        if !dbexits {
        }
    }

    func applicationDocumentsDirectoryFile() -> String {
        let documentDirectorys:NSArray = NSSearchPathForDirectoriesInDomains(.DocumentDirectory, .UserDomainMask, true)
        let documetDirectory = documentDirectorys[0] as!String
        let path = documetDirectory.stringByAppendingString(FILE_NAME)
        
        return path
    }
    
    @IBAction func loadBundle(sender: AnyObject) {
        let path = NSBundle.mainBundle().pathForResource("WeChat_1468557469", ofType: "png")
        var image = UIImage(contentsOfFile: path!)
        self.imageView.image = UIImage(named:"WeChat_1468557469.png")

    }
    @IBAction func loadSandbox(sender: AnyObject) {
        let path = self.applicationDocumentsDirectoryFile()
        self.imageView.image = UIImage(contentsOfFile:path)

    }

    @IBAction func loadWebService(sender: AnyObject) {
        NSLog("从云服务器中加载图片")
    }

}

OC代码

//对文件进行预处理，判断在Documents目录下是否存在plist文件，如果不存在则从资源目录下复制一个。
-(void)createEditableCopyOfDatabaseIfNeeded
{
    NSFileManager *fileManager=[NSFileManager defaultManager];
    NSString *writableDBPath=[self applicationDocumentsDirectoryFile];
    
    BOOL dbexits=[fileManager fileExistsAtPath:writableDBPath];
    if (!dbexits) {
        NSString *defaultDBPath=[[[NSBundle mainBundle] resourcePath] stringByAppendingPathComponent:@"Contacts.plist"];
        
        NSError *error;
        BOOL success=[fileManager copyItemAtPath:defaultDBPath toPath:writableDBPath error:&error];
        
        if (!success) {            
            NSAssert1(0,@"错误写入文件：‘%@’",[error localizedDescription]);
        }
    }
}

//获取放置在沙箱Documents目录下的文件的完整路径
-(NSString *)applicationDocumentsDirectoryFile
{
    NSString *documentDirectory=[NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) lastObject];
    NSString *path=[documentDirectory stringByAppendingPathComponent:@"Contacts.plist"];
   
    return path;
}