Question

I have a android project and within that project I have a folder that contain some images.Now what i want is to access that folder within a jni function. So how should I do that?

Answer 1

An Android application is essentially a zip file, but there are a lot of nice helpers to get to those resources. First thing you need to remember is that these files are not actually in a folder, unless you put them there.

That said, there are a number of possible solutions for you situation.

JNI (almost) all the way

The most JNI-y way to go about things is to use have a method like

private native void processResources(AssetManager assets);

in your Activity, and use JNI to pry all the necessary resources from it, put them somewhere on disk, and process them.

Mix in a bit of Java

Probably an easier way is to have some Java code that helps with the resource management; something like

private void processAll() {
    for (String resource : getResources().getAssets().list(mydir)) {
        process(getResources().getAssets().open(resource));
    }
    // exception handling omitted for readability
}

private void process(InputStream in) throws IOException {
    ByteArrayOutputStream out = new ByteArrayOutputStream();
    byte[] buf = new byte[1024];
    for (int read = in.read(buf); read > 0; read = in.read(buf)) {
        out.write(buf, 0, len);
    }
    process(out.toByteArray());
}

private native void process(byte[] resource);

and do the native processing based on the byte[].

Prepare files on the file system

A third solution is to move the files out of your bundle and onto the file system, and then point your native code to that directory.

So?

In the end, it all depends on what you exactly want to do with your resources, and whether or not they really need to be on the file system. I would keep things as close to Java as possible, and only go native when you really have to (e.g., your image manipulation code).