IOS学习笔记22—文件操作（NSFileManager）结合相册小例子

这个示例程序主要用到了IOS中的UIImageView、UIImagePickerViewController、UIImage、NSFileManager等知识，结合这些知识构成一个小的应用程序，主要功能是对相册图片进行读取、存储到指定文件夹、从指定文件夹读取出来。这方面的知识在正式项目中用的是比较多的。做Android开发中，经常会使用到将图片保存到SD卡和从SD卡读取图片的操作，相比于Android在这方面的操作，IOS要方便许多。

基本功能是从相册选取一张图片，选完后显示在界面的UIImageView控件中，点击保存到文件夹按钮后就将图片保存到Documents下的ImageFile文件夹中，以image.png命名。退出程序下次进来时，可以选择从文件夹读取图片，如果有则读取出来显示在UIImageView上，如果没有则提示文件不存在。

首先来看看最后效果：

·从相册选取图片后显示在界面上

这里对功能进行了一点改进，点击打开相册按钮后出来一个UIActionSheet操作选项框，可以选择是从相机获取图片还是从相册获取。代码也做出了一点修改。

·点击保存到文件夹按钮后提示信息

·点击读取图片按钮后的提示信息（图片不存在）

·如果存在则将图片显示出来

保存图片成功后，按照前一篇文章提到的方法，可以到Finder下查看文件信息：

下面是实现部分，首先看看布局文件：

下面是代码：

#import <UIKit/UIKit.h>

@interface ViewController : UIViewController<UIImagePickerControllerDelegate,UINavigationControllerDelegate,UIActionSheetDelegate>

@property (retain, nonatomic) IBOutlet UIImageView *imageView;
@property (retain, nonatomic) UIButton *saveToFileButton;

//打开相册
- (IBAction)openAlbum:(id)sender;

//从文件夹读取图片
- (IBAction)readImage:(id)sender;

@end

下面是ViewController.m文件

#import "ViewController.h"
//保存到文件夹按钮的标签，选取图片前，这个按钮是隐藏的
#define SAVE_BUTTON_TAG 101

@interface ViewController ()

@end

@implementation ViewController
@synthesize imageView = _imageView;
@synthesize saveToFileButton = _saveToFileButton;

- (void)viewDidLoad
{
    [super viewDidLoad];
    //根据设置的tag获取按钮控件
    self.saveToFileButton = (UIButton *)[self.view viewWithTag:SAVE_BUTTON_TAG];
    //添加对象事件
    [self.saveToFileButton addTarget:self action:@selector(saveToFileBtnTapped:) forControlEvents:UIControlEventTouchUpInside];
    //设置为不可见
    self.saveToFileButton.hidden = YES;
}

- (void)viewDidUnload
{
    [self setImageView:nil];
    [self setSaveToFileButton:nil];
    [super viewDidUnload];
    // Release any retained subviews of the main view.
}

- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation
{
    return (interfaceOrientation != UIInterfaceOrientationPortraitUpsideDown);
}

- (void)dealloc {
    [self.imageView release];
    [self.saveToFileButton release];
    [super dealloc];
}

- (IBAction)openAlbum:(id)sender {
    UIActionSheet *actionSheet = [[UIActionSheet alloc] initWithTitle:@"选择图片" delegate:self cancelButtonTitle:@"取消" destructiveButtonTitle:nil otherButtonTitles:@"拍照",@"相册", nil];
    [actionSheet showInView:self.view];
    [actionSheet release];
}

//从文件夹读取图片
- (IBAction)readImage:(id)sender {
    NSString *imagePath = [self imageSavedPath:@"image.png"];
    NSFileManager *fileManager = [NSFileManager defaultManager];
    //判断文件是否存在
    if (![fileManager fileExistsAtPath:imagePath]) {
        UIAlertView *alertView = [[UIAlertView alloc] initWithTitle:@"Note" message:@"文件不存在" delegate:self cancelButtonTitle:@"OK" otherButtonTitles:nil, nil];
        [alertView show];
        [alertView release];
    }else {
        //从指定目录读取图片
        UIImage *image = [UIImage imageWithContentsOfFile:imagePath];
        self.imageView.image = image;
    }
}

//保存到文件按钮事件
- (void)saveToFileBtnTapped:(id)sender {
    NSString *imagePath = [self imageSavedPath:@"image.png"];
    BOOL isSaveSuccess = [self saveToDocument:self.imageView.image withFilePath:imagePath];
    
    if (isSaveSuccess) {
        UIAlertView *alertView = [[UIAlertView alloc] initWithTitle:@"操作结果" message:@"保存图片成功" delegate:self cancelButtonTitle:@"OK" otherButtonTitles:nil, nil];
        [alertView show];
        [alertView release];
    }else {
        UIAlertView *alertView = [[UIAlertView alloc] initWithTitle:@"操作结果" message:@"保存图片失败" delegate:self cancelButtonTitle:@"OK" otherButtonTitles:nil, nil];
        [alertView show];
        [alertView release];
    }
}

//将选取的图片保存到目录文件夹下
-(BOOL)saveToDocument:(UIImage *) image withFilePath:(NSString *) filePath
{
    if ((image == nil) || (filePath == nil) || [filePath isEqualToString:@""]) {
        return NO;
    }
    
    @try {
        NSData *imageData = nil;
        //获取文件扩展名
        NSString *extention = [filePath pathExtension];
        if ([extention isEqualToString:@"png"]) {
            //返回PNG格式的图片数据
            imageData = UIImagePNGRepresentation(image);
        }else{
            //返回JPG格式的图片数据，第二个参数为压缩质量：0:best 1:lost
            imageData = UIImageJPEGRepresentation(image, 0);
        }
        if (imageData == nil || [imageData length] <= 0) {
            return NO;
        }
        //将图片写入指定路径
        [imageData writeToFile:filePath atomically:YES];
        return  YES;
    }
    @catch (NSException *exception) {
        NSLog(@"保存图片失败");
    }
    
    return NO;
    
}

//根据图片名将图片保存到ImageFile文件夹中
-(NSString *)imageSavedPath:(NSString *) imageName
{
    //获取Documents文件夹目录
    NSArray *path = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *documentPath = [path objectAtIndex:0];
    //获取文件管理器
    NSFileManager *fileManager = [NSFileManager defaultManager];
    //指定新建文件夹路径
    NSString *imageDocPath = [documentPath stringByAppendingPathComponent:@"ImageFile"];
    //创建ImageFile文件夹
    [fileManager createDirectoryAtPath:imageDocPath withIntermediateDirectories:YES attributes:nil error:nil];
    //返回保存图片的路径（图片保存在ImageFile文件夹下）
    NSString * imagePath = [imageDocPath stringByAppendingPathComponent:imageName];
    return imagePath;
}

#pragma Delegate method UIImagePickerControllerDelegate
//图像选取器的委托方法，选完图片后回调该方法
-(void)imagePickerController:(UIImagePickerController *)picker didFinishPickingImage:(UIImage *)image editingInfo:(NSDictionary *)editingInfo
{
    if (image != nil) {
        //选定照片后在界面显示照片并把保存按钮设为可见
        self.imageView.image = image;
        self.saveToFileButton.hidden = NO;
    }
    //关闭图像选择器
    [self dismissModalViewControllerAnimated:YES];
}

-(void)actionSheet:(UIActionSheet *)actionSheet clickedButtonAtIndex:(NSInteger)buttonIndex
{
    //获取图片选取器
    UIImagePickerController *imagePicker = [[UIImagePickerController alloc] init];
    //指定代理
    imagePicker.delegate = self;
    //打开图片后允许编辑
    imagePicker.allowsEditing = YES;
    
    //判断图片源的类型
    if (buttonIndex == 0) {
        if ([UIImagePickerController isSourceTypeAvailable:UIImagePickerControllerSourceTypeCamera]) {
            //相机
            imagePicker.sourceType = UIImagePickerControllerSourceTypeCamera;
        }
    }else if (buttonIndex == 1) {
        if([UIImagePickerController isSourceTypeAvailable:UIImagePickerControllerSourceTypePhotoLibrary]){
            //图片库
            imagePicker.sourceType = UIImagePickerControllerSourceTypePhotoLibrary;
        }
//        if([UIImagePickerController isSourceTypeAvailable:UIImagePickerControllerSourceTypeSavedPhotosAlbum]) {
//            //相册
//            imagePicker.sourceType = UIImagePickerControllerSourceTypeSavedPhotosAlbum;
//        }
    }else if (buttonIndex == [actionSheet cancelButtonIndex]) {
        return;
    }
    
    //打开图片选择模态视图
    [self presentModalViewController:imagePicker animated:YES];
    [imagePicker release];

}

@end

中间有些操作过程我就没有一一例举了，比如如何将控件与代码关联，如何设置控件的TAG等。需要代码的朋友可以给我留言，我发你们邮箱！

欢迎关注我的新浪微博和我交流：@唐韧_Ryan