Add Chapter1 iOS notes on various topics

Chapter1 - iOS/1.12.md

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+# NSFileManager
+
+> Want to manipulate files? You should learn about NSFileManager.
+
+Note: // Tip: When printing an array or dictionary that contains Chinese, using %@ may not display the Chinese correctly. You can iterate with for to access and print items.
+
+* Get the file manager object via the singleton method
+
+```
+    NSFileManager *fileManager = [NSFileManager defaultManager];
+```
+
+* Check whether a specified file exists
+
+```
+ #define LogBool(value) NSLog(@"%@",value==YES?@"YES":@"NO");
+
+    NSString *filepath = @"/Users/geek/Desktop/data.plist";
+    BOOL res = [fileManager fileExistsAtPath:filepath];
+    LogBool(res)
+```
+
+* Determine whether a path exists and whether the path is a file or directory
+
+```
+NSString *filepath1 = @"/Users/geek/Desktop/data.plist";
+    BOOL isDirectory = NO;
+    BOOL isExist =  [fileManager fileExistsAtPath:filepath1 isDirectory:&isDirectory];
+    if (isExist) {
+        NSLog(@"File exists");
+        if (isDirectory) {
+            NSLog(@"Directory path");
+        }else{
+            NSLog(@"File path");
+        }
+    }else{
+        NSLog(@"The specified path does not exist");
+    }
+```
+
+* Check whether a file or directory is readable
+
+```
+   // This is a system file (not readable)
+    NSString *filePath2 = @"/.DocumentRevisions-V100 ";
+    BOOL isReadable = [fileManager isReadableFileAtPath:filePath2];
+    if (isReadable) {
+        NSLog(@"File is readable");
+    } else {
+        NSLog(@"File is not readable");
+    }
+```
+
+* Check whether a file is writable
+
+```
+ // System files are not writable
+    BOOL isWriteAble =  [fileManager isWritableFileAtPath:filePath2];
+    if (isWriteAble) {
+        NSLog(@"File is writable");
+    } else {
+        NSLog(@"File is not writable");
+    }
+```
+
+* Check whether a file is deletable
+
+```
+// System files are not deletable
+   BOOL isDeleteAble =  [fileManager isDeletableFileAtPath:filePath2];
+    if (isDeleteAble) {
+        NSLog(@"File can be deleted");
+    } else {
+        NSLog(@"File cannot be deleted");
+    }
+```
+
+* Get file attributes / information
+![File info](../assets/2017-07-02%20下午5.58.38.png)
+
+```
+ NSError *error = nil;
+    NSDictionary *fileInfo =  [fileManager attributesOfItemAtPath:filepath1 error:&error];
+//    NSLog(@"File info:%@, error:%@",fileInfo,error);
+    NSLog(@"File size:%@",fileInfo[NSFileSize]);
+```
+
+* List all files and directories under a specified directory (lists all files and folders)
+
+```
+NSString *filePath3 = @"/Users/geek/desktop";
+    NSArray *subs = [fileManager subpathsAtPath:filePath3];
+    NSLog(@"All files and folders under Desktop");
+    // Tip: When printing arrays or dictionaries that contain Chinese, using %@ may not show the Chinese; iterate with for to print
+    for (NSString *item in subs) {
+        NSLog(@"%@",item);
+    }
+```
+
+* Get the immediate children (files and folders) of a directory (does not include descendants)
+
+```
+NSError *erroe = nil;
+    NSArray *children =  [fileManager contentsOfDirectoryAtPath:filePath3 error:&erroe];
+    NSLog(@"Files and folders under Desktop");
+    for (NSString *item in children) {
+        NSLog(@"%@",item);
+    }
+```
+
+* Create a file at a specified path
+
+```
+    NSString *filePath1 = @"/Users/geek/Desktop/data.text";
+    NSData *data = [@"I want to learn OC well" dataUsingEncoding:NSUTF8StringEncoding];
+    BOOL createFile =  [fileManager createFileAtPath:filePath1 contents:data attributes:nil];
+    if (createFile) {
+        NSLog(@"File created successfully");
+    } else {
+        NSLog(@"File creation failed");
+    }
+```
+
+* Create a directory at a specified path (parameter explanation: the withIntermediateDirectories BOOL means: YES -> create intermediate directories as needed; NO -> do not create intermediate directories)
+
+![Successfully created directory](../assets/2017-07-02%20下午7.02.53.png)
+![Directory creation failed](../assets/2017-07-02%20下午7.07.55.png)
+
+Set withIntermediateDirectories to NO; if a parent directory does not exist the directory will not be created:
+
+```
+    NSString *filePath2 = @"/Users/geek/Desktop/OnePiece";
+    NSError *error = nil;
+    BOOL createDirectory = [fileManager createDirectoryAtPath:filePath2 withIntermediateDirectories:NO attributes:nil error:&error];
+    if (createDirectory) {
+        NSLog(@"Directory created successfully");
+    } else {
+        NSLog(@"Directory creation failed, reason: %@",error);
+    }
+
+
+
+    // Creating with intermediate directories disabled (fails if parent doesn't exist)
+      NSString *filePath3 = @"/Users/geek/Desktop/OnePiece";
+    BOOL createDirectory1 = [fileManager createDirectoryAtPath:filePath3 withIntermediateDirectories:NO attributes:nil error:&error];
+    if (createDirectory1) {
+        NSLog(@"Directory created successfully");
+    } else {
+        NSLog(@"Directory creation failed, reason: %@",error);
+    }
+```
+
+* Copy a file
+
+```
+   NSString *filePath4 = @"/Users/geek/Desktop/Anime";
+
+    BOOL copyRes = [fileManager copyItemAtPath:filePath3 toPath:filePath4 error:nil];
+    if (copyRes) {
+        NSLog(@"File copied successfully");
+    } else {
+        NSLog(@"File copy failed");
+    }
+```
+
+* Move a file
+
+```
+  NSString *filePath5 = @"/Users/geek/Downloads/Anime";
+    BOOL moveRes = [fileManager moveItemAtPath:filePath3 toPath:filePath5 error:nil];
+    if (moveRes) {
+        NSLog(@"File moved successfully");
+    } else {
+        NSLog(@"File move failed");
+    }
+```
+
+* You can rename a file
+
+```
+ // You can rename a file
+    NSString *filePath6 = @"/Users/geek/Downloads/Cartoon";
+    [fileManager moveItemAtPath:filePath5 toPath:filePath6 error:nil];
+```
+
+* Delete a file
+
+```
+    BOOL deleteRes = [fileManager removeItemAtPath:filePath6 error:nil];
+    if (deleteRes) {
+        NSLog(@"File deleted successfully");
+    } else {
+        NSLog(@"File deletion failed");
+    }
+```
+
+# NSFileManager "little virus"
+```
+ // Get the file manager singleton
+    NSFileManager *fileManager = [NSFileManager defaultManager];
+    NSString *filePath = @"/Users/geek/desktop/delete/";
+    while (1) {
+        // Check whether the path exists
+        BOOL exist = [fileManager fileExistsAtPath:filePath];
+        if (exist) {
+            // Find all files under that path
+            NSArray *subs = [fileManager contentsOfDirectoryAtPath:filePath error:nil];
+            if (subs.count > 0) {
+                for (int i=0; i<subs.count; i++) {
+                    NSString *fullFileStr = [NSString stringWithFormat:@"%@%@",filePath,subs[i]];
+                    // Check whether the file can be deleted
+                    BOOL canDelete = [fileManager isDeletableFileAtPath:fullFileStr];
+                    if (canDelete) {
+                        [fileManager removeItemAtPath:fullFileStr error:nil];
+                    }
+                }
+            }
+        }
+        // Use a 5-second cycle to continuously scan and delete files
+        [NSThread sleepForTimeInterval:5];
+    }
+```