IOS持久化数据----（保存数据的一系列方法)

http://superman474.blog.163.com/blog/static/1206614620118525537389/

数据持久存储到IOS文件系统中有三种不同的机制：属性列表，对象归档，嵌入式数据库SQLite3（另外还有其他方法，可以用传统的C
IO函数读取或者写入数据，也可以使用Cocoa的低级文件管理工具）

每 一个应用程序支持三个文件夹 Documents, Library 和 tmp。应用程序将其数据存储在Documents中，（但基于NSUserDefaults的首选设置除外，它存储在 Library/Preferences文件夹中），当ios设备同步时，不会去备份/tmp中的文件。

1。 下面这句话将返回Documents目录
NSString *Path = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) objectAtIndex:0]
我们可以通过在这个路径结尾附加一个字符串来创建一个文件名，用于执行读取或者写入操作。
NSString *filename = [Path stringByAppendingPathComponent:@"test.txt"];
上面这句话结束之后会filename将包含test.txt文件的完整路径，该文件位于应用程序的Documents目录下，我们可以用filename来创建读取和写入文件。

2。获取对应应用程序临时目录的引用比较方便，
NSString *tmpPath = NSTemporaryDirectory();

3，下面是基本的代码把一个数组写入文件中，（属性列表）
wiriteToFile

NSString *str = @"abc";

NSString *astr = @"efg";

NSArray *Array = [NSArray arrayWithObjects:str, astr, nil];

//Save

NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);

NSString *documentsDirectory = [paths objectAtIndex:0];

if (!documentsDirectory) {

NSLog(@"Documents directory not found!");

}

NSString *appFile = [documentsDirectory stringByAppendingPathComponent:@"Savedatas.plist"];

[[NSArray arrayWithObjects:Array,nil] writeToFile:appFile atomically:NO];

//load

if([[NSFileManager defaultManager] fileExistsAtPath:appFile])

self.SaveDataArray = [NSMutableArray arrayWithContentsOfFile:appFile];

else

self.SaveDataArray = [NSMutableArray arrayWithContentsOfFile:[[NSBundle mainBundle] pathForResource:@"Savedatas" ofType:@"plist"]];

NSArray *strArray = [self.SaveDataArray objectAtIndex:0];

str = [strArray objectAtIndex:0];

astr = [strArray objectAtIndex:1];

4.归档 例子（NSKeyedArchiver）
NSString *str = @"abc";

NSString *astr = @"efg";

NSArray *Array = [NSArray arrayWithObjects:str, astr, nil];

//Save

NSString *Path = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) objectAtIndex:0]; NSString *filename = [Path stringByAppendingPathComponent:@"test"];

[NSKeyedArchiver archiveRootObject:Array toFile:filename];

str = @"a";

astr = @"";

//load

NSArray *arr = [NSKeyedUnarchiver unarchiveObjectWithFile: filename];

str = [arr objectAtIndex:0];

astr = [arr objectAtIndex:1];

NSLog(@"str:%@",str);

NSLog(@"astr:%@",astr);

5.例子（NSUserDefaults）
NSString *str = @"abc";

NSString *astr = @"efg";

NSArray *Array = [NSArray arrayWithObjects:str, astr, nil];

//Save

NSUserDefaults *SaveDefaults = [NSUserDefaults standardUserDefaults];

[SaveDefaults setObject:Array forKey:@"SaveKey"];

str = @"a";

astr = @"";

//load

Array = [SaveDefaults objectForKey:@"SaveKey"];

str = [Array objectAtIndex:0];

astr = [Array objectAtIndex:1];

NSLog(@"str:%@",str);

NSLog(@"astr:%@",astr);

6。下面是从论坛中找的两个便利的方法，用于从存储和读取数据。
如下：
-(BOOL) writeApplicationData:(NSDictionary *)data writeFileName:(NSString *)fileName

{

NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);

NSString *documentsDirectory = [paths objectAtIndex:0];

if (!documentsDirectory) {

NSLog(@"Documents directory not found!");

return NO;

}

NSString *appFile = [documentsDirectory stringByAppendingPathComponent:fileName];

return ([data writeToFile:appFile atomically:YES]);

}

-(id) readApplicationData:(NSString *)fileName

{

NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);

NSString *documentsDirectory = [paths objectAtIndex:0];

NSString *appFile = [documentsDirectory stringByAppendingPathComponent:fileName];

NSDictionary *myData = [[[NSDictionary alloc] initWithContentsOfFile:appFile] autorelease];

return myData;

}

7.最简单的方法将从网络上下载的图片保存到本地~

//将图片保存到本地
+ (void)SaveImageToLocal:(UIImage*)image Keys:(NSString*)key {
NSUserDefaults* preferences = [NSUserDefaults standardUserDefaults];
//[preferences persistentDomainForName:LocalPath];
[preferences setObject:UIImagePNGRepresentation(image) forKey:key];
}

//本地是否有相关图片
+ (BOOL)LocalHaveImage:(NSString*)key {
NSUserDefaults* preferences = [NSUserDefaults standardUserDefaults];
//[preferences persistentDomainForName:LocalPath];
NSData* imageData = [preferences objectForKey:key];
if (imageData) {
return YES;
}
return NO;
}

//从本地获取图片
+ (UIImage*)GetImageFromLocal:(NSString*)key {
NSUserDefaults* preferences = [NSUserDefaults standardUserDefaults];
//[preferences persistentDomainForName:LocalPath];
NSData* imageData = [preferences objectForKey:key];
UIImage* image;
if (imageData) {
image = [UIImage imageWithData:imageData];
}
else {
NSLog(@"未从本地获得图片");
}
return image;
}

8.这是老外分享的一段代码，保存照片的，很简单，呵呵

参数说明：

NSData to retrieve the image from the URL

NSDocumentDirectory to find Document folder’s Path

UIImagePNGRepresentation to save it as PNG

UIImageJPEGRepresentation to save it as JPEG

代码：
NSLog(@”Downloading…”);

// Get an image from the URL below

UIImage *image = [[UIImage alloc] initWithData:[NSData dataWithContentsOfURL:[NSURL URLWithString:@"http://www.objectgraph.com/images/og_logo.png"]]];

NSLog(@”%f,%f”,image.size.width,image.size.height);

// Let’s save the file into Document folder.

// You can also change this to your desktop for testing. (e.g. /Users/kiichi/Desktop/)

// NSString *deskTopDir = @”/Users/kiichi/Desktop”;

NSString *docDir = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) objectAtIndex:0];

// If you go to the folder below, you will find those pictures

NSLog(@”%@”,docDir);

NSLog(@”saving png”);

NSString *pngFilePath = [NSString stringWithFormat:@"%@/test.png",docDir];

NSData *data1 = [NSData dataWithData:UIImagePNGRepresentation(image)];

[data1 writeToFile:pngFilePath atomically:YES];

NSLog(@”saving jpeg”);

NSString *jpegFilePath = [NSString stringWithFormat:@"%@/test.jpeg",docDir];

NSData *data2 = [NSData dataWithData:UIImageJPEGRepresentation(image, 1.0f)];//1.0f = 100% quality

[data2 writeToFile:jpegFilePath atomically:YES];

NSLog(@”saving image done”);

[image release];