Android: retrieving all Drawable resources from Resources object

Question

In my Android project, I want to loop through the entire collection of Drawable resources. Normally, you can only retrieve a specific resource via its ID using something like:

InputStream is = Resources.getSystem().openRawResource(resourceId)

However, I want to get all Drawable resources where I won't know their ID's beforehand. Is there a collection I can loop through or perhaps a way to get the list of resource ID's given the resources in my project?

Or, is there a way for me in Java to extract all property values from the R.drawable static class?

Answer 1

Okay, this feels a bit hack-ish, but this is what I came up with via Reflection. (Note that resources is an instance of class android.content.res.Resources.)

final R.drawable drawableResources = new R.drawable();
final Class<R.drawable> c = R.drawable.class;
final Field[] fields = c.getDeclaredFields();

for (int i = 0, max = fields.length; i < max; i++) {
    final int resourceId;
    try {
        resourceId = fields[i].getInt(drawableResources);
    } catch (Exception e) {
        continue;
    }
    /* make use of resourceId for accessing Drawables here */
}

If anyone has a better solution that makes better use of Android calls I might not be aware of, I'd definitely like to see them!

Answer 2

I guess the reflection code will work but I don't understand why you need this.

Resources in Android are static once the application is installed so you can have a list of resources or an array. Something like:

<string-array name="drawables_list">
    <item>drawable1</item>
    <item>drawable2</item>
    <item>drawable3</item>
</string-array>

And from your Activity you can get it by doing:

getResources().getStringArray(R.array.drawables_list);

Answer 3

If you find yourself wanting to do this you're probably misusing the resource system. Take a look at assets and AssetManager if you want to iterate over files included in your .apk.

Answer 4

i used getResources().getIdentifier to scan through sequentially named images in my resource folders. to be on a safe side, I decided to cache image ids when activity is created first time:

    private void getImagesIdentifiers() {

    int resID=0;        
    int imgnum=1;
    images = new ArrayList<Integer>();

    do {            
        resID=getResources().getIdentifier("img_"+imgnum, "drawable", "com.mobilebabytoys.babyfaces");
        if (resID!=0)
            images.add(resID);
        imgnum++;
    }
    while (resID!=0);

    imageMaxNumber=images.size();
}