给定文件在本地存储中的路径，将文件转换为字节数组？

Question

The following collection contains image paths in the local storage

public ObservableCollection<string> Paths;

These file paths are selected by the user and on the Xamarin Android Player they appear like this:

/storage/emulated/0/Download/img1.jpg
/storage/emulated/0/Download/img2.jpg

Now the problem is the following - I want to convert these selected images (based on their paths) to byte arrays for uploading them to server. In WPF/ ASP.Net this would be easily accomplished by the following code:

byte[] Convert = File.ReadAllBytes("somepath...");

However it appears that there is no such thing available in Xamarin.Forms.

What functions do I need to use in order to in Xamarin.Forms convert image, based on its physical path in local storage to byte array?

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UPDATE

@asp_net Trying to implement your solution:

In my PCL project I've added the following two files:

public interface IFileSystem
{
    byte[] ReadAllByteS(string path);
}

and

public static class FileUtility
{
    public static IFileSystem FileSystem { get; set; }

    public static void SetUp(IFileSystem fs)
    {
        FileSystem = fs;
    }
}

On Android I've added the following file:

class SharedFileSytem : IFileSystem
{
    public byte[] ReadAllByteS(string path)
    {
        return File.ReadAllBytes(path);
    }
}

And I'm kinda lost at the initialization/registering part - I'm pretty sure I need to add something in my MainActivity.cs file.

base.OnCreate(bundle);
Xamarin.Forms.Forms.Init(this, bundle);
//?
LoadApplication(new App());

Because currently, when I'm trying to execute the following code in my PCL code

FileUtility.FileSystem.ReadAllByteS(somepath);

I get the following error message:

"object reference not set to an instance of an object"

Answer 1

To clarify things: System.IO is not available in Portable Class Libraries, which you seem to use. But it is of course available "in Xamarin.Forms".

Options:

1. Use Shared Projects instead of PCL.
2. Call platform-specific code from your PCL.

Example

Define an interface within your PCL.

public interface IFileSystem
{
    byte[] ReadAllByteS(string path);
}

Implement it on each platform (or within a shared project for all platforms in this case).

// Could also be "IosFileSystem" or "SharedFileSytem"
public class DroidFileSystem : IFileSystem
{
    public byte[] ReadAllbytes(string path)
    {
        return File.ReadAllBytes(path);
    }
}

Register your implementation when your app starts (there are libraries out there helping you with that).

public static class Utils
{
    public IFileSystem FileSystem { get; set; }

    public static void SetUp(IFileSystem fs)
    {
        FileSystem = fs;
    }
}

( Utils lives in your PCL but its SetUp method is being called from AppDelegate or your Main Activity.)

Use it:

Utils.FileSystem.ReadAllBytes(...)

Answer 2

You can load image into Memory stream and convert in to array,Something like this should work

using (var streamReader = new StreamReader(path))
 {   
   using (var memoryStream = new MemoryStream())
    {
        streamReader.BaseStream.CopyTo(memoryStream);
        return memoryStream.ToArray();
    }

}

Answer 3

public async static Task<IFile> AsStorageFileAsync(this byte[] byteArray, string fileNameEx)
    {
        IFile file = await StorageData.LocalStorage().CreateFileAsync(fileNameEx, CreationCollisionOption.ReplaceExisting);
        using (var fileHandler = await file.OpenAsync(FileAccess.ReadAndWrite))
        {              
            byte[] dataBuffer = byteArray;
            await fileHandler.WriteAsync(dataBuffer, 0, dataBuffer.Length);
        }
        return file;
    }