Develop Reference

Where are the resources' IDs?

Android will allocate ids for each pics in the res/drawable directory. Where are they?
I want to dynamically choose one pic form the pool and show it. How can I do that?

They are stored in the res/drawable folder.
If the file name is demo.png, then they can be accessed by R.drawable.demo
If you want to access a random drawable, store all the resource identifiers in a Integer ArrayList, and programatically generate a random function using Random(), and get that particular item from the arraylist. Then you'll have a random drawable every time.

Autogenerated ids are in the gen file, but not advisable to use them. It would be better to use the filenames directly through some predefined array of R.drawable.filename and randomly pick them.

There IDs are stored in the R.java file, but you cannot edit it, as your changes are over written each time.
You can also access resources by name, which may be a viable approach to solving your problem if you know the names of the resources or can derive them according to some pre-defined naming scheme. (for example images are named in the sequence image1, image2 and so on.
You have to map the name to the identifier using the getIdentifier() method of the Resources class.
String name = "resource" + rng.nextInt(count);
int resource = getResources().getIdentifier(name, "drawable", "com.package");
The documentation for this method says:
Note: use of this function is
discouraged. It is much more efficient
to retrieve resources by identifier
than by name.
This is true but need not be a problem if you are doing it in code that isn't performance sensitive.
Alternatively, if you don't mind listing the resources in XML, you could create a typed array that you can then randomly select from.

How to add R.drawable resources to an array for android?

I would like to have sequence of set R.drawable been called in integer array so that it can be accessed later with choice.But I'll like to load to the R.drawable dynamically which corresponds to different names.It names needs to be had as per the external value input not hardcoded.I tried this in making many but like use list,set,array conversion etc.Kindly guide me with a snippet or example on this regard.Thank you.

I suppose, that best way to achieve this funcionality is by using ArrayAdapter of Integer.
You will simply add drawble resources by id.
If you need to get resource id, but you will get string input from user, you can use this code:
Android, getting resource ID from string?

Changing value of R.String Programmatically

Can you change the values of a R.string programmatically in an android program? I need to pull some API information (for example battery state, battery percentage, android os version) and would like to save it a R.string value. I know how to read it:
String helloValue= getResources().getString(R.string.hello);
I've also looked at: Change value of R.string programically? but it seems that only involves changing language and he ended up doing it a different way. Can anyone lend a hand please? I've also looked here: http://developer.android.com/guide/topics/resources/string-resource.html and found nothing to help out either :(

You can't change strings.xml dynamically since it's a compiled resource. There are other mechanisms for saving data in Android, here's a nice post that covers this topic: Data Storage. Hope this helps.

If you need to save small amounts of String information you should be using SharedPreferences that's exactly what it's for :)

There are many ways to finish your ideas. But, you cannot change your String resource, (as well as R.java resource), or layout resource,... and any other resource. You can do this by change resource to assets. this can read and write :)

You can get value from res/string value by this way.
String str = getResources().getString(R.string.<name_of_value>);
Now you can further use this value of this(str) String variable.
But according to me there is no way to set value of res/string

Keep Strings into .txt file or put them into a Database?

Hey, I have a lot of Strings that I use into my app, the .txt file that I use has ~14000 lines.. and each 3-10 lines are divided into sections like <String="Chapter I"> ... </String> ..
Speaking of performance/speed, should I put the sections into a Database, Or read line by line through the .txt file and check if the section number is the current one? Will this affect speed/performance?
I could also divide each ~2000 lines into a different .txt file so there would be less lines to go through. Is this a bad way of storing data? Thanks

I think sqlite would do the trick. It will probably be way faster than parsing a text file, plus you wont have to maintain the headache of your own ad hoc text database, or build a parser in the first place. Basically, use it, its way easier.

The standard way to deal with Strings in Android is to put them into res/values/strings.xml (I'm pretty sure you can have multiple String files in that directory if you like). If you are developing in Eclipse it will automatically populate the R class (the resource class) with constants that you can use to reference these Strings in your code:
R.string.mystring
Or in XML layouts:
#string/mystring
Or if you're doing something more custom you can use:
String string = getString(R.string.hello);
I would definitely choose this over a .txt file. It's much easier. All the work is done for you! Have a read of this Android article about it.

This is what a database is for. Use it.

Android Bitmap syntax

I want to load bitmaps into ImageViews in Android, but I don't want to use the R.drawable syntax because I have a lot of images with a standard naming convention so it's much easier to get the image with some logic. For example, all my images are named:
img1.png
img2.png
img3.png
So if a user selects a value, let's say x, I show "img" + x + ".png" in the ImageView. Looks like Bitmap.decodeFile is what I need, but I need to know the syntax of how to get to my drawables folder since that's where the images are. Or if there's perhaps a better way.
I realize I could do this with a switch statement instead of concatenating the image name but that would be a lot of lines since I have so many images.

One alternative is to use reflection to load images from R. You can looking static variables by string name. Keep in mind that reflection can be slow though. If you are going to be loading the same image multiple times, you might want to keep a cache of name -> R id.
Edit:
You can also access them by URI. See referring to android resources using uris.

The R.drawable value is a number by itself. You just need to use the first image id and add a fixed value to find the right image. For example:
R.drawable.image1 = 1234;
R.drawable.image2 = 1235;
etc.
So to get image 2 I would to R.drawable.image1 + 1.
Every time the R.java file is regenerated the numbers may change but the sequence will be the same. If you don't want to depend in this then you will have to look at the "assets" folder.

Looks like I've found a solution. The real problem is that I generate the resource names at runtime, but I can get the resource id like this:
getResources().getIdentifier("string1" + string2, "id", "com.company.package")
I can then pass that value to setImageResource or any other method that accepts a resource id.