Develop Reference

How should I store common strings?

I can store them in res/strings
<resources>
<string name="str1">app</string>
</resources>
And I can store them in static const
public static final string str1 = "app"
Which one is better?
I mean that which one will use more memory and which one will make package larger.

If you have to change some text in your app's view, then you don't have to find where you have written that text. You simply go to the strings.xml in res folder and can change the string. For that reason, the first option will always be the better option.
If you want a string that will be used as a key in your app then you can store it in a static constant variable. Like: If you want to pass data through intent or in any other way, at that time you have to pass a key. That key will be a string and can be stored in a static constant variable.

it's really depend if you treat strings as constants or not.
If you string are constants (e.g. string that will be sent as key of intent) then you can either create some Constants class or define it as a constant in your activity/fragment class. If those string are texts that will be displayed on your application UI then they should be defined as resources in your application.
BTW all the resources string can be localized to different languages
If you need more info or examples please let me know.

The package size:
I believe that "Ran Hassid"'s comment describes well about the package size.
Memory usage:
Just create an android apk file with some static final strings and then decompile it. You will see that the variable has no initial value in the compiled version and the value is replaced in all references!
For example check this sample from my decompiled apk which is also obfusicated by proguard:
public static String f10850f;
...
...
...
hashMap.put(C1554f.m14687a("\u0014]SCVQ^V"), str);
here is the actual code I have written:
public static String packageName="\u0014]SCVQ^V";
...
...
...
hashMap.put(EncryptorClass.decrypt(packageName), str);
In this case, the static final String variable in my written code has value of "\u0014]SCVQ^V" but it is not used in run-time and just copy/pasted in related pieces of code.
So using static final String variables needs no memory because variable has no initial value.
Have a look at android docs about using static final variables
Also take a look at this post regarding memory of variables with no value
Overally, I use static final variables and string resources for different purposes like code encryption, language support and whether I want to access the variable using a Context or not.

How to store resource file with same name but different extensions in android

I am working on one static custom Android Media Player Application where i have many media files stored in raw folder.
Where as some files have same name but different extensions, here android is giving me
res\raw\then.mp4:0: error: Resource entry then is already defined.
res\raw\then.mp3:0: Originally defined here..
Can anybody please suggest me something on this?
Also there are few media files with java keywords like if, else, return, switch, case,class, else, final, long, new, this,true... where android is giving me error of invalid symbol.
Please suggest me solution for that also.
Thanks in advance...

As #blackbelt said, it's not possible, I'll just add that you can instead put your files in the assets directory instead of res.
You will not be able to use them like R.id.file, but you will get more flexibility.

simply you can't. Raw is build at compile-time inside R.java, and the name key must follow the java convention for naming. Since
if, else, return, switch, case,class, else, final, long, new,
this,true
are reserved keywords you can not use them.
Edit: R.java would look lie:
public static final class raw {
public static final int if=0x70000;

Handle soft labels in Android

I am building an application and use labels in the following areas.
1. Component Names (TextView, Buttons etc)
2. Buttons in alert boxes
3. Parameters to AsyncTask
4. Key names in Intent extras
5. Log tags
I have got strings.xml files to store and use labels. I am using using it for category 1. What do you think is the best option for others?
res/strings.xml or
Constants class ?

I'll suggest to you what I normally do:
For everything that the user will read on the screen or be referenced in anyway from a XML layout, use strings.xml. I reckon that includes your 1 and 2. But remember that for AlertDialogues you can also use android.R.string.ok or android.R.string.cancel, etc; that will vary from use to use.
Also for project config values, or API keys, you could have a config.xml with String, Integers, etc. Something that makes easy to later on change those values without diving into the code.
For AsyncTask, it varies a lot of what work it is doing, but usually a network, DB or disk operation, and I try to include private static final String URL_PT1 = "http://..."; etc, in the classes themselves, as they are the only interested in knowing that address (or DB columns, or file prefix)
For key names (both in Intent and Fragment arguments) I use private static final String KEY_VALUE = "renjith.Key.MyClassName.VALUE"; and then create a public static Bundle getIntentExtras(String value) inside that class that will properly allocate the value in the extra. That's because only that one class needs to know about it's KEY values, there's no reason to make those public accessible, that will just create errors for outside classes doing it wrong.
For Logs (5), create on every class a private static final String TAG = "Renjith.ThisClassName"; (and for Fragments make the TAG public to be used in transactions). That way you can create a filter in LogCat Renjith.* and you can easily identify from where this log is coming from
edit:
For sharedpreferences it depends:
for GlobalSharedPreferences I would create one class to handle them with static set/get methods that must receive Context and all keys private static inside that class.
For local shared preferences (that only one class is interested in saving/retrieving) I would handle in a SharedPreferences file with the same name as that class and all the keys as private static inside that one class.
Again, same philosophy, only the classes that really need to know about those details will know about them, and abstracting to the rest of the classes with direct method calls.

How can I initialize the Sender ID for Android C2DM without using a hard-coded value in a static variable?

I'm adding Android C2DM to a Android library project. I started with the com.google.android.c2dm package that is included with JumpNote and Chrome To Phone. In order to use this package, you have to subclass the C2DMBaseReceiver service which takes the Sender Id as an argument to it's constructor. In JumpNote, this argument is initialized using a hard-coded static variable in a config class. However, in an Android library project, which may be used by multiple concurrently running apps I don't think I can use a hard-coded static variable (that is, I believe it could lead to problems when/if multiple apps are trying to access/modify the static variable).
I tried to think of a way to initialize the Sender Id without using a static variable and am stumped so far.
The obvious solution would be to use the Manifest or a Resource string or a combination of the 2. For example, in strings.xml I might have a "ac2dmSender" string, which is accessed in a meta-data child of the C2DMReceiver service declaration in the manifest. However, it seems that you cannot get a reference to the PackageManager or ResourceManager from a static context, so there is no way for me to then retrieve the meta data in such a way as to pass it in to the constructor of C2DMBaseReceiver.
Please let me know that I'm missing something! Thanks in advance.

We had same problem.
We solved it by using properties file under the assets folder.
Can load the properties staticly by using static configuration helper class.
On the first time the application is loaded can get the properties file using the Application context.
for example:
1. init the static configuration
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
myConfig = new WLConfig(getApplication());
}
Then use in the configuration class:
myProperties.load(context.getAssets().open("myclient.properties"));
And get the sender email:
return myProperties.getProperty(WL_C2DM_SENDER)

However, in an Android library project, which may be used by multiple concurrently running apps I don't think I can use a hard-coded static variable (that is, I believe it could lead to problems when/if multiple apps are trying to access/modify the static variable).
"Multiple concurrently running apps" each have their own copy of the static variable, since each runs in its own process.

Cannot get resource from android application

I am building an Android app, and I have a problem to get resource from string.xml.
I need to have a URL in String.xml that will be used several times through the app.
I tried Resources.getText("my_url"), but this does not work. Eclipse complains when I use this.
Do you think this is the best way to do ?

What you probably want is:
String myUrl = getString(R.string.my_url);
The getString() method is in Context which means that it's available directly in your Activity class since Activity is a subclass of Context. (The getString() method is also in Resources but it's easier to call on it directly on your Activity.)
What happens with your XML resources is that each is given a unique integer ID and this is added to the automatically generated R class as a public static final int. You then use these IDs to reference the resources. Have a look in the gen folder in your Eclipse project and you'll find the R class in there.

Do you ever refer this page: https://developer.android.com/guide/topics/resources/available-resources.html ?
If you want to retrieve the String represented by a resource ID, you can call the Context.getString() method.
Or, you have to post Eclipse's complains.