最近几年来，地理信息系统无论是在理论上还是应用上都处在一个飞速发展的阶段。 GIS被应用于多个领域的建模和决策支持，如城市管理、区划、环境整治等等，地理信息成为信息时代重要的组成部分之一； “数字地球”概念的提出，更进一步推动了作为其技术支撑的GIS的发展。 与此同时，一些学者致力于相关的理论研究，如空间感知、空间数据误差、空间关系的形式化等等。 这恰好说明了地理信息系统作为应用技术和学科的两个方面，并且这两个方面构成了相互促进的发展过程。
9.35.1. Brief introduction ¶
File processing can not be explained intuitively through the application, we can understand the file processing of IOS from the following examples.
The operation of files in IOS. Because the application is in the sandbox, the access to read and write to the file is restricted, and you can only read and write the file in several directories.
9.35.2. Methods used in file processing ¶
The following is a list of methods used to access and manipulate files.
In the following example you must replace the FilePath1, FilePath, and FilePath strings with the full file path to get the desired operation.
Check whether the file exists
NSFileManager *fileManager = [NSFileManager defaultManager]; //Get documents directory NSArray *directoryPaths = NSSearchPathForDirectoriesInDomains (NSDocumentDirectory, NSUserDomainMask, YES); NSString *documentsDirectoryPath = [directoryPaths objectAtIndex:0]; if ([fileManager fileExistsAtPath:@""]==YES) { NSLog(@"File exists"); } Compare the contents of two files
if ([fileManager contentsEqualAtPath:@"FilePath1" andPath:@" FilePath2"]) { NSLog(@"Same content"); } Check for writable, readable, and executable files
if ([fileManager isWritableFileAtPath:@"FilePath"]) { NSLog(@"isWritable"); } if ([fileManager isReadableFileAtPath:@"FilePath"]) { NSLog(@"isReadable"); } if ( [fileManager isExecutableFileAtPath:@"FilePath"]){ NSLog(@"is Executable"); } Move Fil
if([fileManager moveItemAtPath:@"FilePath1" toPath:@"FilePath2" error:NULL]){ NSLog(@"Moved successfully"); } Copy a file
if ([fileManager copyItemAtPath:@"FilePath1" toPath:@"FilePath2" error:NULL]) { NSLog(@"Copied successfully"); } Delete a file
if ([fileManager removeItemAtPath:@"FilePath" error:NULL]) { NSLog(@"Removed successfully"); } Read a file
NSData *data = [fileManager contentsAtPath:@"Path"]; Write to a file
[fileManager createFileAtPath:@"" contents:data attributes:nil];