Absolute fastest way to save and read data from text file or binary file
Read and write a file using a StorageFile object. Also see the File access sample. You can learn how to get a file by using a file picker in Open files and folders with a picker. Here's how to write to a writable file on disk using the StorageFile class.
The common first step for each of the ways of writing to a file unless you're writing to the file immediately after creating it is to get the file with StorageFolder. First, call ConvertStringToBinary to get a buffer of the bytes based on an arbitrary string that you want to write to your file. First, open the file by calling the StorageFile. It returns a stream of the file's content when the open operation completes.
Next, get an output stream by calling the GetOutputStreamAt method from the stream. Put this in a using statement to manage the output stream's lifetime.
Now add this code within the existing using statement to write to the output stream by creating a new DataWriter object and calling the DataWriter. Lastly, add this code within the inner using statement to save the text to your file with StoreAsync and close the stream with FlushAsync. Here's how to read from a file on disk using the StorageFile class. The common first step for each of the ways of reading from a file is to get the file with StorageFolder.
Then use a DataReader object to read first the length of the buffer and then its contents. Open a stream for your file by calling the StorageFile. It returns a stream of the file's content when the operation completes. Get an input stream by calling the GetInputStreamAt method.
Put this in a using statement to manage the stream's lifetime. Specify 0 when you call GetInputStreamAt to set the position to the beginning of the stream. Lastly, add this code within the existing using statement to get a DataReader object on the absolute fastest way to save and read data from text file or binary file then read the text by calling DataReader.
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IO classes to work with files and directories in iOS that you would use in any. However, despite the familiar classes and methods, iOS implements some restrictions on the files that can be created or accessed and also provides special features for certain directories. This article outlines these restrictions and features, and demonstrates how file access works in a Xamarin. You can use Xamarin. IO classes in the. The File class lets you create, delete, and read files, and the Directory class allows you to create, delete, or enumerate the contents of directories.
You can also use Stream subclasses, which can provide a greater degree of control over file operations such as compression or position search within a file. This article discusses the features and restrictions of the iOS file system in detail, and includes a sample application that demonstrates how to use Xamarin.
IO classes for file system operations on iOS. The following code snippets illustrate some common file operations. This code enumerates the subdirectories in the current directory specified by the ". Your output will be a list of all the files and folders that are deployed with your application displayed in the console window while you are debugging.
To read a text file, you only need a single line of code. This example will display the contents of a text file in the Application Output window. Although working with the complete System. Xml namespace is beyond the scope of this article, you can easily deserialize an XML document from the file system by using a StreamReader like this:.
Xml namespace for more information about serialization. You should also review the Xamarin. This sample shows how to use the Environment class to access the Documents folder where we can create files and directories.
For more information about the System. Working with Json data in a Xamarin. Simply add the NuGet package to your application's project:. Finally, create an instance of the Account class, serialize it to json data and write it to a file:. NET's documentation for more information about working with json data in a. Despite the similarities between Xamarin. NET in some important ways. In order to include a file in the assembly, you must mark it with a special build action, called Content. This could be confusing for.
This means if your filename casing differs between the file itself and the references to it in code, your code might still work in the simulator but that it would fail on a real device.
Combine method, which adjusts for the current platform, rather than hardcode a particular path separator. This is a simple step that makes your code more portable to other platforms. This restriction is known as the Application Sandbox. In terms of the file system, your application is limited to creating and deleting files and directories in its home directory. The home directory is a unique location in the file system where your application and all its data are stored. You cannot choose or change the location of the home directory for your application; however iOS and Xamarin.
The Application Bundle is the folder that contains your application. It is distinguished from other folders by having the. Your Application Bundle contains your executable file and all the content files, images, etc. When you browse to your Application Bundle in Mac OS, it appears with a different icon than you see in other directories and the. Right-click on this icon and choose View Package Contents to browse the contents of the Application Bundle directory.
The contents appear just like the contents of a regular directory, as shown here:. When your application is installed on a device, the operating system creates its home directory and places your Application Bundle inside.
Your code can access the Application Bundle to read data, but nothing should be written to that root directory, as it is signed and any modifications will invalidate your application and prevent it from launching. So, although nothing should be written to the root directory, in iOS 7 and earlier creates a number of directories within the application root directory that are available for use. The earlier directory and file examples accessed the Documents directory. To write to another directory you must construct a path using the ".
These files can be accessed in iTunes when the device is connected and the user chooses the Apps tab. For example, the following screenshot shows the files in selected app shared via iTunes:. Users can only access the top-level items in this directory via iTunes. They cannot see the contents of any subdirectories although they can copy them to their computer or delete them. Your application should take this into consideration and be resilient to destructive updates of the Documents folder.
The sample code for this article creates both a file and a folder in the Documents folder in SampleCode. This screenshot shows how these appear in iTunes:. Refer to the Working with Images article for information about how to set icons for the application and for any custom document types you create. If the UIFileSharingEnabled key is false or not present, then file sharing is, by default, disabled and users will not be able to interact with your Documentsdirectory.
Backing up a large amount of data can take a long time. If you decide you need to back up any particular document or data, your application should only use the Documents and Library folders for this. For transient data or files that can be easily retrieved from the network, use either the Caches or the tmp directory. Apple introduced iCloud Backup functionality with iOS 5.
This feature provides the user with a complete backup in case their device is lost, stolen or damaged. To comply with the iOS Data Storage Guidelines you should limit the amount of data that gets backed up by adhering to the following items:.
When SetSkipBackupAttribute is true the file will not be backed-up, regardless of the directory it is stored in even the Documents directory. You can query the attribute using the GetSkipBackupAttribute method, and you can reset it by calling the SetSkipBackupAttribute method with falselike this:.
Since App Extensions run as part of a host application as opposed to their containing appthe sharing of data isn't automatic included so extra work is required. App Groups are the mechanism iOS uses to allow different apps to share data. If the applications have been properly configured with the correct entitlements and provisioning, they can access a shared directory outside of their normal iOS sandbox.
This value must also be referenced in each project's Entitlements. The iOS app and the extension can also share files using a common file path given they have been properly configured with the correct entitlements and provisioning:. If the Group Path returned is nullcheck the configuration of the entitlements and the provisioning profile and make sure that they are correct. When a new version of your application is downloaded, iOS creates a new home directory and stores the new Application Bundle in it.
This article showed that file system operations are as simple with Xamarin. It also introduced the Application Sandbox and examined the security implications that it causes. Next, it explored the concept of an Application Bundle. Finally, it enumerated the specialized directories available to your application and explained their roles during application upgrades and backups.
Our new feedback system is built on GitHub Issues. For more information on this change, please read our blog post. General File Access Xamarin. Working with directories This code enumerates the subdirectories in the current directory specified by the ". Xml namespace is beyond the scope of this article, you can easily deserialize an XML document from the file system by using a StreamReader like this: Creating Files and Directories This sample shows how to use the Environment class to access the Documents folder where we can create files and directories.
WriteAllText filename, "Write this text into a file" ; Creating a directory is a very similar process: Combine documents, "NewDirectory" ; Directory. CreateDirectory directoryname ; For more information about the System. Serializing Json Working with Json data in a Xamarin. Simply add the NuGet package to your application's project: WriteAllText filename, json ; Refer to Json.
Special Considerations Despite the similarities between Xamarin. The contents appear just like the contents of a regular directory, as shown here: Application Directories When your application is installed on a device, the operating system creates its home directory and places your Application Bundle inside.
These directories and their purposes are listed below: If you need to access the content files inside your Application Bundle, the path to this directory is available via the NSBundle. The contents of this directory can be made available to the user through iTunes file sharing although this is disabled by default. As long as sensitive files remain hidden, these files will not be exposed and potentially moved, modified, or deleted by iTunes if file sharing is enabled in a future version.
You can use the Environment. MyDocuments method to get the path to the Documents directory for your application. The contents of this directory are backed up by iTunes. The contents of this directory are never exposed to the user via iTunes. You can create your own subdirectories in Library; however, there are already some system-created directories here that you should be aware of, including Preferences and Caches.
The contents of this directory except for the Caches subdirectory are backed up by iTunes.
The standard approach for getting information from a text file is using the openreadand close functions. When you've finished with the file, you should close the connection, using:. However, the recommended way to read a file in Julia is to wrap any file-processing functions inside a do block:. The open file is automatically closed when this block finishes. See Controlling the flow for more about do blocks. Or you can use readlines to read in the whole file as an array, with each line an element:.
You might find the chomp function useful — it removes the trailing newline from a string. The eachline function turns a source into an iterator. This allows you to process a file a line at a time:. Another approach is to read until you reach the end of the file. Typically you also want to keep track of which line you're on:. An easier approach is to use enumerate on an iterable object — you'll get the line numbering for free:.
If you have a specific function that you want to call on a file, you can use this alternative syntax:. This opens the file, runs the bigUpFunc function on it, then closes it again, assigning the processed contents to the variable. You can use readcsv and readdlm functions to read lines from CSV files or files delimited with certain characters, such as data files, arrays stored as text files, and tables.
And if you use the DataFrames package, there's also a readtable specifically designed to read data into a table. To work on a restricted selection of files in a directory, use filter and an anonymous function to filter the file names and just keep the ones you want. If you want to match a group of files using a regular expression, then use ismatch. To examine a file hierarchy, use walkdirwhich lets you work through a directory, and examine the files in each directory in turn.
If you want information about a specific file, use stat "pathname"and then use one of the fields to find out the information. Here's how to get all the information and the field names listed for a file "i":. To work on specific files that meet conditions — all IPython files modified after a certain date, for example — you could use something like this:.
The cpmvrmand touch functions have the same names and functions as their Unix shell counterparts. To convert filenames to pathnames, use abspath. You can map this over a list of files in a directory:. To restrict the list to filenames that contain a particular substring, absolute fastest way to save and read data from text file or binary file an anonymous function inside filter — something like this:. To write to a text file, open it using the "w" flag and make sure that you have permission to create the absolute fastest way to save and read data from text file or binary file in the specified directory:.
The convenient writedlm and readdlm functions let you write an array or collection to a file. The elements are separated absolute fastest way to save and read data from text file or binary file tabs unless you specify another delimiter. Here, a colon is used to delimit the numbers:. Since it's so common to use files where the elements are separated with commas rather than tabs CSV filesJulia provides "-csv" versions of these "-dlm" functions, writecsv and readcsv.
As ever, refer to the official documentation for options and keywords. There are also a number of Julia packages specifically designed for reading and writing data to files, including DataFrames. Look through the Julia package directory for these and more. From Wikibooks, open books for an open world. A Scandal in Bohemia 4 II. A Case of Identity 6 IV. The Boscombe Valley Mystery A Scandal in Bohemia 29II.
A Case of Identity 35IV. The Boscombe Valley Mystery … 62the island of Mauritius. As to Miss Violet Huntermy friend 60Holmesrather to my disappointmentmanifested no further 66interest in her when once she had ceased to be the centre of one 65of his problemsand she is now the head of a private school at 70Walsallwhere I believe that she has met with considerable success.