Android, getting resource ID from string?

Question

I need to pass a resource ID to a method in one of my classes. It needs to use both the id that the reference points to and also it needs the string. How should I best achieve this?

For example:

R.drawable.icon

I need to get the integer ID of this, but I also need access to the string "icon".

It would be preferable if all I had to pass to the method is the "icon" string.

Kessiah

is it possible in similar way to getId of files saved to internal storage? I have problem cause I should supply array of ids instead of locations to my gallery (thought it's adapter).. thanks – Onrush

@Ewoks: They don't have IDs on internal storage. They're just images, if anything you need to load them into a bunch of Image objects and pass those, you might want to start a new question though. – Kessiah

possible duplicate of How to get a resource id with a known resource name? – Pendulous

Answer 1

@EboMike: I didn't know that Resources.getIdentifier() existed.

In my projects I used the following code to do that:

public static int getResId(String resName, Class<?> c) {

    try {
        Field idField = c.getDeclaredField(resName);
        return idField.getInt(idField);
    } catch (Exception e) {
        e.printStackTrace();
        return -1;
    } 
}

It would be used like this for getting the value of R.drawable.icon resource integer value

int resID = getResId("icon", R.drawable.class); // or other resource class

I just found a blog post saying that Resources.getIdentifier() is slower than using reflection like I did. Check it out.

WARNING: This solution will fail in the release build if code/resource shrinking is enabled as suggested by Google: https://developer.android.com/build/shrink-code
Also, it might fail for some other cases, e.g. when you have <string name="string.name">…</string> the actual field name will be string_name and not the string.name

Immediate

@Macarse: Presently, getIdentifier() has to do two reflection lookups. In your example above, getIdentifier() would use reflection to get Drawable.class, then another reflection lookup to get the resource ID. That would account for the speed difference. That being said, neither are especially quick and therefore really need to be cached (particularly if used in a loop, or for rows in a ListView). And the reflection approach's big problem is that it makes assumptions about the internals of Android that might change in some future release. – Glaucescent

@CommonsWare: That's right. I was checking how android implemented and it ends ups being a native call. gitorious.org/android-eeepc/base/blobs/… => gitorious.org/android-eeepc/base/blobs/… – Immediate

Sorry guys, I still don't see an acceptable answer. I want to minimize parameters not increase them. how about if I pass the resource Id (R.drawable.icon) as an integer, can I then use the id to get the resource name and strip just the part I need to get "icon"? – Kessiah

@Hamid: If you can pass R.drawable.icon to your method you can just do it like you said: methodName(int R.drawable.icon, "icon");. I don't know why you want to do that, thought. – Immediate

@Marcarse: I just want to pass the one, myMethod(int R.drawable.icon) and the method will use the int as the resource to load, and find "icon" as the string to identify it. – Kessiah

@Hamid: Well, maybe you should tell us exactly what you want? You wanted to convert a string to an ID, you got two solutions for that. Tell us what you're trying to do, what data you have and what you don't have, and we can adjust the answers. If you have the ID as an int, then why do you need to convert a string to an int? – Impatient

I'm loading some images, I need a string to identify each image, and I need the id (int) that will let me get the image from the resources. I would like the identifying string to be the filename (minus extension) that is at the end of the R.drawable.filename (int) that I can pass to the method. – Kessiah

I would use an integer array with the IDs instead. Using strings for IDs doesn't sound like the right approach. – Impatient

I accept this answer because of the solutions suggested in the comments by EboMike. Integer IDs was definately the way to go. – Kessiah

Why the context parameter? – Juetta

Always return -1 for me. – Dina

Calling should be getId("icon", R.drawable.class); not getResId("icon", context, Drawable.class); – Cumin

How do I use this look up a string? Which class should I pass as the second parameter – Athome

you should follow this #3476930 – Retortion

to help others: if this flexible solution works for a while but it starts to throw NoSuchFieldException, it can be caused by proguard obfuscator: the class in question is being obfuscated. (more resources are mapped to the same class/field). In my case the error happend only when installed from the play store (aab). Solution: in the catch try to get it by Resources.getIdentifier() or disable proguard. – Mneme

DON'T use this! This solution might look neat, but it will come back to bite you. As mentioned by CommonsWare "the reflection big problem is that it makes assumptions about the internals of Android that might change in some future release". And if you check SO comments that's already happened to quite a few people who discovered the method above fails in production, if minification is enabled. One should either map string names to int ids in the code, or if absolutely needed use the Resources.getIdentifier provided by the Android SDK combined with the @SuppressLint("DiscouragedApi") – Bradstreet

Answer 2

You can use this function to get resource ID.

public static int getResourceId(String pVariableName, String pResourcename, String pPackageName) 
{
    try {
        return getResources().getIdentifier(pVariableName, pResourcename, pPackageName);
    } catch (Exception e) {
        e.printStackTrace();
        return -1;
    } 
}

So if you want to get for drawable call function like this

getResourceId("myIcon", "drawable", getPackageName());

and for string you can call it like this

getResourceId("myAppName", "string", getPackageName());

Read this

Reparative

What is the point of making a function that simply calls another one and "handles" a possible exception? Call getResources().getIdentifier() directly. – Etch

Upvoted for clarifying how to pass in the type to get different kinds or resources. The android dev documentation does not have details and "id" from a prior answer does not work for strings. – Bona

Is there also the opposite? Meaning from R.string.some_string to "some_string" ? – Tiliaceous

Use of getIdentifier is discouraged because resource reflection makes it harder to perform build optimizations and compile-time verification of code – Nolte

Answer 3

This is based on @Macarse answer.

Use this to get the resources Id in a more faster and code friendly way.

public static int getId(String resourceName, Class<?> c) {
    try {
        Field idField = c.getDeclaredField(resourceName);
        return idField.getInt(idField);
    } catch (Exception e) {
        throw new RuntimeException("No resource ID found for: "
                + resourceName + " / " + c, e);
    }
}

Example:

getId("icon", R.drawable.class);

Haukom

Answer 4

How to get an application resource id from the resource name is quite a common and well answered question.

How to get a native Android resource id from the resource name is less well answered. Here's my solution to get an Android drawable resource by resource name:

public static Drawable getAndroidDrawable(String pDrawableName){
    int resourceId=Resources.getSystem().getIdentifier(pDrawableName, "drawable", "android");
    if(resourceId==0){
        return null;
    } else {
        return Resources.getSystem().getDrawable(resourceId);
    }
}

The method can be modified to access other types of resources.

Sidekick

now .getResources().getDrawable is deprecated if(android.os.Build.VERSION.SDK_INT >= android.os.Build.VERSION_CODES.LOLLIPOP){ return mContext.getDrawable(resourceId); } else { return mContext.getResources().getDrawable(resourceId); } – Tomlinson

also use of getIdentifier is discouraged because resource reflection makes it harder to perform build optimizations and compile-time verification of code – Nolte

Answer 5

If you need to pair a string and an int, then how about a Map?

static Map<String, Integer> icons = new HashMap<String, Integer>();

static {
    icons.add("icon1", R.drawable.icon);
    icons.add("icon2", R.drawable.othericon);
    icons.add("someicon", R.drawable.whatever);
}

Whaling

Answer 6

Simple method to get resource ID:

public int getDrawableName(Context ctx, String str){
    return ctx.getResources().getIdentifier(str,"drawable", ctx.getPackageName());
}

Endodontics

Would be better if you just give some more information to your answer. – Mihalco

Use of getIdentifier is discouraged because resource reflection makes it harder to perform build optimizations and compile-time verification of code – Nolte

Answer 7

I did like this, it is working for me:

    imageView.setImageResource(context.getResources().
         getIdentifier("drawable/apple", null, context.getPackageName()));

Jugoslavia

Thanks. Works as expected. I used the following: view.context.resources.getIdentifier("drawable/item_car_$position", null, context.packageName). – Moulton

Use of getIdentifier is discouraged because resource reflection makes it harder to perform build optimizations and compile-time verification of code – Nolte

Answer 8

You can use Resources.getIdentifier(), although you need to use the format for your string as you use it in your XML files, i.e. package:drawable/icon.

Impatient

My answer below is the reverse of this. Pass in the resource id, and then use getResourceEntryName(id) to find the string name. No messing to find "icon" from the longer text. – Judgeship

Answer 9

Since you said you only wanted to pass one parameter and it did not seem to matter which, you could pass the resource identifier in and then find out the string name for it, thus:

String name = getResources().getResourceEntryName(id);

This might be the most efficient way of obtaining both values. You don't have to mess around finding just the "icon" part from a longer string.

Judgeship

Answer 10

A simple way to getting resource ID from string. Here resourceName is the name of resource ImageView in drawable folder which is included in XML file as well.

int resID = getResources().getIdentifier(resourceName, "id", getPackageName());
ImageView im = (ImageView) findViewById(resID);
Context context = im.getContext();
int id = context.getResources().getIdentifier(resourceName, "drawable",
context.getPackageName());
im.setImageResource(id);

Burra

Answer 11

The Kotlin approach

inline fun <reified T: Class<*>> T.getId(resourceName: String): Int {
            return try {
                val idField = getDeclaredField (resourceName)
                idField.getInt(idField)
            } catch (e:Exception) {
                e.printStackTrace()
                -1
            }
        }

Usage:

val resId = R.drawable::class.java.getId("icon")

Or:

val resId = R.id::class.java.getId("viewId")

Disquietude

This works but what exactly is this doing? It has a very weird syntax. How is it performance wise? – Laborsaving

This doesn't work with proguard/minify enabled. – Louvenialouver

Answer 12

In your res/layout/my_image_layout.xml

<LinearLayout ...>
    <ImageView
        android:id="@+id/row_0_col_7"
      ...>
    </ImageView>
</LinearLayout>

To grab that ImageView by its @+id value, inside your java code do this:

String row = "0";
String column= "7";
String tileID = "row_" + (row) + "_col_" + (column);
ImageView image = (ImageView) activity.findViewById(activity.getResources()
                .getIdentifier(tileID, "id", activity.getPackageName()));

/*Bottom code changes that ImageView to a different image. "blank" (R.mipmap.blank) is the name of an image I have in my drawable folder. */
image.setImageResource(R.mipmap.blank);  

Syndic

Answer 13

In MonoDroid / Xamarin.Android you can do:

 var resourceId = Resources.GetIdentifier("icon", "drawable", PackageName);

But since GetIdentifier it's not recommended in Android - you can use Reflection like this:

 var resourceId = (int)typeof(Resource.Drawable).GetField("icon").GetValue(null);

where I suggest to put a try/catch or verify the strings you are passing.

Hutchens

Answer 14

For getting Drawable id from String resource name I am using this code:

private int getResId(String resName) {
    int defId = -1;
    try {
        Field f = R.drawable.class.getDeclaredField(resName);
        Field def = R.drawable.class.getDeclaredField("transparent_flag");
        defId = def.getInt(null);
        return f.getInt(null);
    } catch (NoSuchFieldException | IllegalAccessException e) {
        return defId;
    }
}

Antiicer

Answer 15

    ImageId.substring(0, ImageId.length()-1);

    imageMessage = (ImageView) findViewById(R.id.imageMessage);

    int resID = getResources().getIdentifier(ImageId , "drawable", getPackageName());

    imageMessage.setImageResource(resID);

Dont forget to add substring

Largo