How to store Image Resource/Name in preferences

Question

I have a scenario:

Suppose, there are two images: one.png and two.png. User will have to select an image, I have to save image's name or Resource ID in preferences. Later when user will open the app, I will load the image user selected last time.

So my Question is how am I going to save it in preferences? Is saving Resource ID for image correct? Does R.java contents remain same once app is installed? I just don't want to save bitmap anywhere since it is already present in drawables.

Please help me clear my concept. Thanks.

"Does R.java contents remain same once app is installed?" Its contents do not change after it's being compiled to an APK. HOWEVER, the integer ID assigned to each variable may well change when you modify your code to create a new APK in the future, so no you shouldn't store the integer ID. — Kai, Dec 11 '14 at 08:52
@Kai Thanks for information. I wish I could give u +1 for this :) — NightFury, Dec 11 '14 at 09:45

score 3 · Accepted Answer · answered Dec 11 '14 at 08:47

3

You should save the name, i.e (one, two in your case)

Later, you can get IDs of resources by name

String imageNameFromPreferences= getLastUsedImageFromPref();
//get resource id by name
final int resourceIdOfLastUsedImage = resources.getIdentifier(imageNameFromPreferences, "drawable", 
   context.getPackageName());
//use this id to set the image anywhere
imageView.setBackgroundResource(resourceIdOfLastUsedImage)

answered Dec 11 '14 at 08:47

Vinay W

9,912
8
41
47

Sure that the id will never change on an update? I won't be sure. – rekire Dec 11 '14 at 08:55
It will change, every time the app compiles. That is why we are retrieving the dynamically generated id using a fixed string identifier every time we run the app. – Vinay W Dec 11 '14 at 09:15
Thanks. This is technique I was looking for. – NightFury Dec 11 '14 at 09:43

score 1 · Answer 2 · edited Dec 11 '14 at 08:52

I would just save a hint which image was displayed the last time. I would use something like "img1" and "img2". Then the next time in onCreate load the correct image. In general, saving the resource id should work fine, but if you add and remove new images, it is possible that the ids change. However this can only happen after an update.

Try this code in your onCreate method:

SharedPreferences prefs = context.getSharedPreferences(BuildConfig.APPLICATION_ID + "_preferences", Context.MODE_PRIVATE);
String lastImg = settings.getString("image");
if("img1".equals(lastImg) {
    imageView.setDrawable(R.drawable.img1);
} else if("img2".equals(lastImg) {
    imageView.setDrawable(R.drawable.img2);
}

Thanks for your answer. But this will make my app very complex to handle, since it have tons of images. — NightFury, Dec 11 '14 at 09:44

Kelevandos · Answer 3 · 2014-12-11T08:47:57.640

Do something like this:

public List<Integer> myImagesList;

public void createMyImagesList{
    //Here put all the image ids you need into the list
    myImagesList.put(R.id.one);
    myImagesList.put(R.id.two);
}

And later, when you want to store the user selection, simply store the List position of the selected image.

public Integer obtainUserSelectedImage(int theIdStoredInPrefs){
    return myImageList.get(theIdStoredInPrefs);
}

This way you create a wrapper id, independent from the R.drawable id, as the list will be repopulated with valid ids each time the app is re-run (and possibly, re-built).

Thanks for answer, but this doesn't suit my situation. – NightFury Dec 11 '14 at 09:42 — NightFury, Dec 11 '14 at 09:42

How to store Image Resource/Name in preferences

3 Answers3