Access to Application.persistentDataPath within hololens app?

ckesterson · August 2016

Hello!!

In my application, I would like to be able to take a picture, and then access the picture within the same code. I have the picture being taken successfully, and I can look at it through the Hololens web portal. But when I try to access the picture using the file path and file name the picture was JUST saved to, I get the following error:

"Exception thrown: 'System.IO.FileNotFoundException' in System.IO.FileSystem.dll
FileNotFoundException: Could not find file 'C:\Data\Users\"

et cetera. What could be the issue here? I'm storing the initial file path and file name in a variable, and then using that same variable to try and access the picture a few lines down. Is this an issue with accessing Application.persistentDataPath? That's where I'm currently storing the picture once it is taken.

Thank you so much for any help or ideas!

Patrick · August 2016

you need: using System.Linq;

Moving the code block down (into the other function) is probably what you want to do.

here's why you would need to move it:
1. You call TakePhotoAsync. That function returns immediately, but the photo hasn't been taken yet. Who knows when the photo will be taken and saved to disk. It could be immediate, and it could be several seconds.
2. But then you try to read the file even though it probably hasn't been made yet. So you get a file not found.
3. The callback function is called after the file is made, so in there the file should exist, and if it's in the applicationData folder you should be able to read it in to upload.

ahillier · August 2016

Hi @ckesterson,
You might try saving your pictures to one of the 'Known Folders':
https://developer.microsoft.com/en-us/windows/holographic/App_model.html#app_file_storage

I would suggest saving pictures to the 'PicturesLibrary' and then edit your appxmanifest capabilities to include access to that folder.

ckesterson · August 2016

Patrick · August 2016

Would you mind posting your script? I can take a look.

ckesterson · August 2016

@Patrick Sure, this was the function I'm having trouble with... A lot of it is actually from the code that you had posted on the other forum you just answered my question on. I was hoping to avoid using your workaround way of storing a picture to persistentDataPath and THEN moving it somewhere else, so I was thinking maybe I could hard code the path to the Pictures folder on the hololens? Or just somewhere that I can then send it to an API after, so it needs to be somewhere that is accessible. Do you think CameraRoll would be better for this, and if so, how can I get the file path to it?

private void OnPhotoModeStarted(PhotoCapture.PhotoCaptureResult result)
{
string filePath = null;
if (result.success)
{
// capturing a frame to memory---
string filename = string.Format(@CapturedImage{0}_n.jpg, Time.time);
filePath = System.IO.Path.Combine(Application.persistentDataPath, filename);

            try
            {
                photoCaptureObject.TakePhotoAsync(filePath, PhotoCaptureFileOutputFormat.JPG, OnCapturedPhotoToDisk);

            }
            catch (System.ArgumentException e)
            {
                Debug.LogError("System.ArgumentException:\n" + e.Message);
            }
        }
        else
        {
            Debug.LogError("Unable to start photo mode!");
        }

        // ADDING IN API CODE CALL
        if (!(filePath == null)) {
            Debug.Log ("Starting Coroutine UploadJPG");
            string uploadURL = "https://theAPI.com";
            StartCoroutine (UploadJPG (filePath, uploadURL));
        } else
            Debug.Log ("API cannot be run, no file path set.");
    }

Patrick · August 2016

Where does UploadJPG come from? I'm assuming that's where the file not found is hitting occuring.

ckesterson · August 2016

Here is my UploadJPG function, it's below the OnPhotoModeStarted function in the same class. I definitely think that's where it's occurring as well, I'm guessing it's unable to find the file path when it tries to convert the JPG file there into bytes.

IEnumerator UploadJPG (string localFilePath, string uploadURL) {

        // Read bytes from JPG file
        string bytes = System.Convert.ToBase64String (System.IO.File.ReadAllBytes(localFilePath));

        // Create form containing Base64String representation of JPG
        WWWForm form = new WWWForm ();
        form.AddField ("image_bytes", bytes);

        // Upload form to web
        WWW upload = new WWW(uploadURL,form);        
        yield return upload;
        if (upload.error == null)
            Debug.Log("upload done :" + upload.text);
        else
            Debug.Log("Error during upload: " + upload.error);

    }

Patrick · August 2016

Is the failure happing on this line?

 // Read bytes from JPG file
        string bytes = System.Convert.ToBase64String (System.IO.File.ReadAllBytes(localFilePath));

Give me a few and I'll see if I can get you past this line.

and to answer your other question...

you can't just save to the pictures folder from an API that runs inside of the Unityplayer.dll because the UnityPlayer.dll doesn't have the same 'capabilities' as your actual application. It's also likely that a unity api also cannot read from the pictures folder for the same reason.

ckesterson · August 2016

@Patrick well so I don't want to save to the pictures folder FROM the API, I am able to take pictures from within my app currently. What I haven't been able to do yet is then take that picture, convert it to a base64 string of bytes, and then send THAT to an API. It's currently saving the photo correctly, and I can see the photo from the Web Portal, but it seems like my application is unable to get back to where the photo was stored.

Patrick · August 2016

Do you care if the picture ever is stored on the device?

ckesterson · August 2016

@Patrick I think that it's preferable that it be stored, but if it'd be easier to not have it stored (or if it isn't possible to do what I'm trying to do), then I would certainly welcome not storing it as a temporary fix. I guess the only parts that _definitely _ need to happen are that the picture get taken, that the picture is stored as a base64 string of bytes, and that the string of bytes is then sent to the API. So if not storing the picture is an easy workaround, then I'm all ears

Patrick · August 2016

It's way easier if you don't want to store the picture. It looks something like:

photoCaptureObject.TakePhotoAsync((memoryResult, memoryData) =>
            {
                if (memoryResult.resultType == PhotoCapture.CaptureResultType.Success)
                {
                    List<byte> buffer = new List<byte>();
                    memoryData.CopyRawImageDataIntoBuffer(buffer);
                    string bytes = System.Convert.ToBase64String(buffer.ToArray());

// and now you have your bytes as a string, you can upload them or whatever.

                }
            });

Patrick · August 2016

OHHHHHHH!!!!!!!!

I see a major problem with the code you posted.

This block:

        if (!(filePath == null)) {
            Debug.Log ("Starting Coroutine UploadJPG");
            string uploadURL = "https://theAPI.com";
            StartCoroutine (UploadJPG (filePath, uploadURL));
        } else
            Debug.Log ("API cannot be run, no file path set.");

should really be in the OnPhotoCapturedToDisk function.

ckesterson · August 2016

@Patrick I'll try that now and get back to you, thank you!!!

--------------------edit-----------------------------

would you recommend simply moving that block of code down instead? Also what is the reasoning behind moving that block of code?

Patrick · August 2016

you need: using System.Linq;

Moving the code block down (into the other function) is probably what you want to do.

here's why you would need to move it:
1. You call TakePhotoAsync. That function returns immediately, but the photo hasn't been taken yet. Who knows when the photo will be taken and saved to disk. It could be immediate, and it could be several seconds.
2. But then you try to read the file even though it probably hasn't been made yet. So you get a file not found.
3. The callback function is called after the file is made, so in there the file should exist, and if it's in the applicationData folder you should be able to read it in to upload.

ckesterson · August 2016

@Patrick ahhhh okay that makes a lot of sense!! Wow that's frustrating, thank you so much for your help! So persistentDataPath should be okay for what I need to do then? I shouldn't need to change that?

Patrick · August 2016

I think so.

ckesterson · August 2016

It worked!!!!!!!!!!!! Thanks so much, you rock!!

Access to Application.persistentDataPath within hololens app?

Best Answer

Answers