CODEWITHSUNDEEP
androidandroid-resources
Don Subert
Don Subert

Reputation: 2676

Android resources problem: How to getIdentifier for a res/drawable-hdpi folder?

In an Android application, I am trying to get a list of files that are in res/drawable-hdpi

My understanding is that I should be able to get the unique identifier for a subfolder of res, and then iterate through the fields of R to filter files that aren't within a range of the folder's ID.

int directoryId = getResources().getIdentifier("drawable-hdpi", "drawable", getPackageName());

Field[] fields = R.drawable.class.getFields();
for (Field field : fields) {
    int resourceId = field.getInt(null);
    if (resourceId >= directoryId && resourceId < (directoryId + 100)) {
        // resourceId is a file in the drawable-hdpi directory
    }
}

However, the directoryId is set to 0. I understand that this is the expected behavior if

  1. The directory doesn't exist
  2. The name of the directory doesn't fit the pattern
  3. The directory is being explicitly excluded

However, none of these things is the case, so I'm really confused. Here's the folder structure

res
├── drawable
│   ├── ic_launcher_background.xml
│   ├── ic_launcher_foreground.xml
│   └── ic_wallpaper_black_24dp.xml
├── drawable-hdpi
│   ├── img1.jpg
│   ├── img2.jpg
│   └── img3.jpg
...

It's the img1.jpg, img2.jpg, and img3.jpg, that I'm interested in. I can see them in the list of fields of R, so the folder must be being included. I've triple checked that the folder meets the naming requirements.

What am I doing wrong?

Upvotes: 1

Views: 142

Answers (1)

CommonsWare
CommonsWare

Reputation: 1006859

I am trying to get a list of files that are in res/drawable-hdpi

That is not possible at runtime. You could create a Gradle task or other compile-time script that examines your hard drive and generates something that contains this information (Java code using JavaPoet, JSON file as an asset, etc.). Or, instead of using res/, you could put your images in assets/, then use getAssets().list() on a Context to iterate over the assets (warning: libraries may also package assets, so don't assume they are all yours).

My understanding is that I should be able to get the unique identifier for a subfolder of res, and then iterate through the fields of R to filter files that aren't within a range of the folder's ID.

There are some problems with this:

  • Resource directories do not have IDs

  • From your standpoint, resource IDs are random numbers that can change from build to build

  • R represents all resources in a unified identifier space, not ones tied to some particular set of resource qualifiers (e.g., your strings, drawables, layouts, dimensions, and so on all get R values, in semi-arbitrary order).

I understand that this is the expected behavior

It is the expected behavior all the time. I do not know where you saw otherwise.

Upvotes: 2

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