Develop Reference

Android Wear: How to send multiple items with MessageApi?

So i want to use the MessageApi and not the DataApi to send multiple items to the wearable. However the sendMessage() of the MessageApi only allows a byte array to be sent.
For reference:
Wearable.MessageApi.sendMessage(mGoogleApiClient,
String id,
String path,
byte[] bytes)
My guess would be to create an array of byte arrays and then serialize that into one big byte array and send it off.
To make things clearer these are the steps in pseudo code:
byte[][] arrayOfByteArrays;
String a --> convert to byte[];
Bitmap b --> convert to byte[];
Add a and b byte[]'s to arrayOfByteArrays;
Serialize arrayOfByteArrays to just a byte[] and send it off;
Is this the correct approach? or Should I just call sendMessage() multiple times? Thanks.

In general, it is more efficient (battery, bandwidth, ...) to send one message instead of multiple ones. However, there may be other factors involved in your specific case that may warrant sending multiple messages. Looking at your pseudo code, I noticed you are also trying to send a bitmap using the MessageApi. That, in general, is not the best approach to send across an image, or other types of assets; you can use Assets or you can use ChannelApi. Otherwise, the approach of serializing a bunch of small objects and putting them into one byte array and then desrializing at the other end would work; one simple way to do so (if dealing with simple objects) is to use json as a serialization means.

How to store and manipulate chunks of byte[] data in Java for Android (AudioRecord)

I am in no way a seasoned programmer. I have been successful at getting AudioRecord to write microphone data directly to file (as a readable .wav file) as it comes in from the mic, with the help of many code snippets from the internet.
However, for what I want to do with my app, I need to save only portions of what comes in from the mic, and I thought I would be able to do that by saving the byte data into some sort of an array first so I could selectively use what I want and save to file. Like many examples do, my class for reading microphone data reads the data into a byte array defined as:
byte data[] = new byte[audioBuffer];
and is read in with
read = audio.read(data, 0, audioBuffer);
My idea was to save each byte data array after it is read in to some sort of another array, and then read back each individual byte data array later to save to file when the user requests it. I tried an ArrayList to hold the data arrays:
private ArrayList<byte[]> grabArray = new ArrayList<byte[]>(grabArraySize);
but I am apparently only getting the last byte data array from the microphone for the whole .wav file. I am guessing I am misusing the ArrayList, but it's description sounded like the best chance of being able to do what I need. I have tried to find another way to do what I want including ByteBuffer, but that does not seem to provide the type of control that an array provides, where I can overwrite old data with new, and then at any point retrieve any or all of the data.
Basically, I know how to do this if it were simple primitives like integers or floats, but byte arrays are apparently throwing me for a loop. On top of that, there is a byte primitive, then there is the Byte class which can be wrapper... all a bunch of ??? to someone who doesn't make a living programming in Java. What is the best way to manhandle byte arrays (or just bytes for that matter) like you would do with just plain numbers?
Some more code to show how I save the audio data (in my AudioRecord thread) to a temporary holding array, then try to retrieve the data (in another class) so I can save to file: (My code is a big mess right now with comments and me trying various methods, commenting out things I'm not currently using... it would be too much to put it all here and I don't have the time to clean it up. I'm hoping this description of how I am trying to handle byte arrays will be enough to the help I need.)
Reading audio data and saving to my temporary holding array:
while(recordState){
read = audio.read(data, 0, audioBuffer);
if(AudioRecord.ERROR_INVALID_OPERATION != read){
if(i_read == grabArraySize){
i_read = 0; // reset index to 0 if hit end of array size
}
grabArray.set(i_read, data);
i_read += 1;
}
}
When asked to, reading audio data back from temporary holding array so I can save to file:
while(i < grabArraySize - 1){ // not writing the whole array - leaving out the last chunk
if(i_write == grabArraySize){
i_write = 0;
}
os.write(tempArray.get(i_write));
i += 1;
i_write += 1;
}
My FileOutputStream os works fine - I am successfully writing to file with the .wav header. I need to figure out how to store the data[ ] byte arrays from the AudioRecorder somewhere other than directly to a file, so that I can then retrieve them whenever I want, and then write them to file. I am successfully getting audio data, but the whole file is repeating one piece of that audio data (of size audiobuffer) over and over into whole file. The file is the correct length; everything else seems to be working; I can even recognize the sound I was making in the little bit that gets saves over and over...
Update again - It appears that ArrayLists are just pointers, as opposed to holding values like a normal array of values. I am now defining grabArray and tempArray both as byte[ ][ ]. Example - if I want to hold 10 separate byte arrays, with each byte array of size audioBuffer, I would define my array as such:
byte[][] grabArray = new byte[10][audioBuffer];
Now, in my AudioRecord thread, I am looping through my grabArray, setting each index = to the incoming audio byte array:
grabArray[i] = data;
Then, when I'm ready to write out to file, (after setting tempArray = grabArray ; I do this in case the AudioRecord thread writes a new audio chunk to the grabArray before I get to write to file) I loop through my tempArray:
os.write(tempArray[i]);
I am still getting only one instance of data[ ] (the audio chunks) repeated all throughout the file. Am I at least on the right track?

getting image from byte array in JSON object to android app

Heres my situation:
I have a RESTful WCF service running on my server, the service is meant to get various types of data about people from a database and makes that data available as a single JSON object. It works great!
[EDIT]There is another service that maintains an image cache in the file system on the server. When a request is sent to the RESTful service, that service then requests an image from the image service. If the image is already in the cache (same width, height and person as the request), it returns that (as a byte array). We MUST use this service to retrieve images.
Now what I want is the image of that person. In our database, the image is a long raw (ew). However, I have dealt with that issue already (previous paragraph). The image is now a Byte array. I am pretty new to android and I am not sure what the best way to retrieve this image is. What I thought I could do was add the byte array to the JSON object and then use the base64 decoder to convert it into a drawable image. However, everytime I try, it times out and tells me it expected ',' or ']' at some arbitrary index of the char buffer for the JSON object.
I have been able to pull the small bits of data out of the JSON object without an issue, but now that there is a huge byte array in it, the JSONObject hates me. What would be a better way to get this image from my service?

Base64 encode the byte array to get a string.
Add the string to JSON object and send it.
When JSON is received, get out the string.
Base64 decode it to get back the byte array.
Use byte array to create Image.

See this question on storing images, it's always better to store this sort of data on file system. If possible deprecate that field, and create a script to move existing images to file system.
You should then store the images on a file system (or some sort of content management system) which can be retrieved by a URL.
Then store the URL in the database. you can then send this in your json object.
{
...
image_url:<url from database>
...
}
When the client receives this it will make a call to that URL and download the image.
Your client will have to make a separate call to retrieve the image but it's generally better than filling your database with binary data. This can also work to your advantage if you want to display data fast while allowing the image to be downloaded in the background.

Better than using Base64 encoding is this way of returning Stream (from WCF RAW programming)
[OperationContract, WebGet]
public Stream GetTestImage(Image image)
{
MemoryStream stream = new MemoryStream();
image.Save(stream, System.Drawing.Imaging.ImageFormat.Jpeg);
stream.Position = 0;
WebOperationContext.Current.OutgoingResponse.ContentType = "image/jpeg";
return stream;
}

Include Small Image in JSON for Android App

My app currently requests a JSON file with some text and other data from my server. I want to add functionality so that it also downloads a very small image (like an icon) through the same file [without creating an additional request]. Is it possible to do so, and how would I go about it (base64?)

Should be eminently reasonable: look at http://developer.android.com/reference/android/util/Base64.html. All you'd need to do is:
Read your icon into a byte[] array on the server.
(Assuming your server is in java) Use something like http://iharder.sourceforge.net/current/java/base64/ to write the byte[] array into a StringOutputStream through http://iharder.sourceforge.net/current/java/base64/api/index.html?Base64.OutputStream.html.
Add the contents of the String to the JSON file.
On the android device call http://developer.android.com/reference/android/util/Base64.html#decode%28java.lang.String,%20int%29 to convert the JSON attribute into a byte[] array.
You can then pass the byte array to http://developer.android.com/reference/android/graphics/BitmapFactory.html#decodeByteArray%28byte[],%20int,%20int,%20android.graphics.BitmapFactory.Options%29 or one of its brethren functions (you may have to play with image formats/encodings to get it to swallow your byte array correctly).
Voila! You have a Bitmap you can use.
Let me know how that works out.

Can large String Arrays freeze my program?

I recently created a program that gets medi-large amounts of xml data and converts it into arrays of Strings, then displays the data.
The program works great, but it freezes when it is making the arrays (for around 16 seconds depending on the size).
Is there any way I can optimize my program (Alternatives to string arrays etc.)

3 optimizations that should help:
Threading
If the program freezes it most likely means that you're not using a separate thread to process the large XML file. This means that your app has to wait until this task finishes to respond again.
Instead, create a new thread to process the XML and notify the main thread via a Handler when it's done, or use AsyncTask. This is explained in more detail here.
Data storage
Additionally, a local SQLite database might be more appropriate to store large amounts of data, specially if you don't have to show it all at once. This can be achieved with cursors that are provided by the platform.
Configuration changes
Finally, make sure that your data doesn't have to be reconstructed when a configuration change occurs (such as an orientation change). A persistent SQLite database can help with that, and also these methods.

You can use SAX to process the stream of XML, rather than trying to parse the whole file and generating a DOM in memory.

If you find that you really are using too much memory, and you have a reason to keep the string in memory rather than caching them on disk, there are certainly ways you can reduce the memory requirements. It's a sad fact that Java strings use a lot of space. They require two objects (the string itself and an underlying char array) and use two bytes per char. If your data is mostly 7-bit ASCII, you may be better of leaving it as a UTF-8 encoded byte stream, using 1 byte per character in the typical case.
A very effective scheme is to maintain an array of 32k byte buffers, and append the UTF-8 representation of each new string onto the first empty space in one of those arrays. Your reference to the string becomes a simple integer: PTR = (buffer index * 32k) + (buffer offset). "PTR/32k" yields the index of the desired byte buffer, and "PTR % 32k" yields the location within the buffer. Use either an initial length byte or a null terminator to keep track of how long the string is. When you need to access one of the strings, don't allocate a new String object: unpack it into a mutable StringBuilder or work directly with the UTF-8 byte representation.
The above approach is obviously a lot more work, but can save you between a factor of 2 and 6 in memory usage (depending on the length of your strings). However, you should beware of premature optimization. If your problem is with the processing time to parse your input, or is somewhere else in your program, you could find that you've done a lot of work to fix something that isn't your bottleneck and thus get no improvement at all.