Loading files within android

问题:

Android seems to make life pretty easy for loading resources of certain types. Once I leave the beaten path a little bit, it seems less helpful. I can load in images, sounds and other objects from the assets folder if and only if they are of certain types. If I try to load a binary file of my own format, I get a less than helpful 'file not found' exception, even though listing the directory shows that it is clearly there.

I've tried using the following methods to read a binary file of a custom format from the assets directory:

File jfile = new File("file://android_asset/"+filename); //tried to get the URI of the assets folder
JarFile file = new JarFile("assets/"+filename); //tried assuming the assets folder is root
fd = am.openNonAssetFd( filename); //tried getting my file as an non asset in the assets folder (n.b. it is definitely there)
fs = am.open(filename, AssetManager.ACCESS_BUFFER); //tried loading it as an asset

I'm thinking that there's something fundamental about android file I/O that I don't understand yet. The documentation for asset management seems incomplete and there must be some reason for deliberately making this unintuitive (something to do with security?). So, what's the fool proof, canonical way of loading a binary file of my own format within an android app?

UPDATE:

I tried file:///android_asset/ but still no joy.

String fullfilename = "file:///android_asset/"+filename;
File jfile = new File(fullfilename);
if (jfile.exists())
{
    return new FileInputStream(jfile);
}
else
{
return null;  //the file does exist but it always says it doesn't. 
}

Are there any permissions for the file or in the project manifest that I need?

Thanks

回答1:

I think the best way to load a file from the Assets folder would be to use AssetManager.open(String filename) - this gives you back an InputStream which you can then wrap in a BufferedInputStream and otherwise call read() to get the bytes. This would work regardless of the file type. What kind of problems have you had with this approach specifically?

回答2:

I think you have left out the slash as in

File jfile = new File("file:///android_asset/"+filename);

There's three forward slashes, not two. :)

回答3:

For me the solution was to uninistall the application, clean the project in Eclipse and run it again. The problem was Android couldn't find the new files I put in the asset folder. I ended up reading this question so I hope this can be helpful to someone else.