How can I add a watch for getSharedPreferences (Where is it stored?)

Question

I've been testing out a few sample weather app code projects looking for a 3 to 5 day forecast one that easily compiles in android studio. I can't find a simple one that is at my level of understanding yet but working with one that might help. (If anyone knows of a simple up to date weather forecast app then note it below please)

First line in question.

if (getSharedPreferences(KEY_PREF, 0).getBoolean(KEY_PREF, true)
            && servicesConnected())

From:

private static final String KEY_PREF = "firstrun";

if (getSharedPreferences(KEY_PREF, 0).getBoolean(KEY_PREF, true)
            && servicesConnected()) {
    if (getSharedPreferences(KEY_PREF, 0).getBoolean(KEY_PREF, true)
            && servicesConnected()) {
        // get current city lat lon
        buildGoogleApiClient();
        mClient.connect();
        CommonUtils.showToast("Retrieving your current location...");
        // this will be done one time only
        getSharedPreferences(KEY_PREF, 0).edit()
                .putBoolean(KEY_PREF, false).apply();
    } else if (savedInstanceState == null) {
        if (DBHelper.getInstance().getCityCount() == 0) {
            // called only if the cities array is empty too add a city
            getSupportFragmentManager()
                    .beginTransaction()
                    .add(R.id.container, new AddCityFragment(),
                            AddCityFragment.class.getSimpleName()).commit();
        } else {
            getSupportFragmentManager().beginTransaction()
                    .add(R.id.container, new WeatherFragment()).commit();
        }
    }

}

According to developer.android.com

boolean getBoolean (String key, boolean defValue) Parameters: (1) String key: The name of the preference to retrieve. (2) defValue boolean: Value to return if this preference does not exist.

My original questions asked:

1. What exactly is getBoolean doing?

2. The documentation doesn't say what mode 0 means in the 2nd parameter of getSharedPreferences (String name, int mode). Any idea what?

3. How can I add a watch for getSharedPreferences to Android Studio's debugging

The Solution that I deduced with the help of you guys:

1. getSharedPreferences(KEY_PREF, 0) is looking for a KEY_PREF preference file on the android device. It returns an object to it which allows us to use getBoolean to determine if there is a key inside it with the same name. In this case it was looking for a "firstrun" file which doesn't exist during first run of the app on the actual android devices storage (saved as cache). Since the key didn't exist on the first run it sets the boolean value as true and continues running inside the if statement. If the key "firstrun" existed and it was set to false then it would return false and skip executing inside that part of the if statement.

2. Mode 0 is MODE_PRIVATE = the default mode, where the created file can only be accessed by the calling application (or all applications sharing the same user ID).

3. When I was trying to debug the issue I noticed that I can add a debugger watch for getSharedPreferences(KEY_PREF, 0) and drill inside the resulting preference file from withing the debugger to see that the mMap parameter to the SharedPreferences object creates a "firstrun" key with the value of "false". It was a first for me to see how it adds this value.

I also found a cool plug-in for android studio for mac and windows which is faster than going into the android device or virtual device and clearing the apps cache. It's called ADB idea and used with the CTRL+ALT+SHIFT+A hotkey combo.

Thanks everyone!

Answer 1

SharedPreference is just a way to store some small-size data.

1) Meaning why would it return true if it doesn't exist?

You can have it return false if you want. That's just the default value for that key. You should set default to true/false depending on the data logic. For their particular case, setting the default true for that key goes with their app logic.

For example, AFAIK android sdk doesn't provide us with any apis that would say that app is running for the first time. So, to know that if the app is running for the first time or not, you could get the boolean value for a key like "is_first_run" and have the default value be true. If the app is run for the first time, then this value would not exist in shared preference because you've not set it yet. So, the default value true makes sense. And if you find it to be true then set it to false, so that the next time the app is run, it'll return false. If you clear the cache, the value will be true once again because the cache is destroyed and the variable no longer exists.

2) question what is operating mode 0 for SharedPreferences getSharedPreferences (String name, int mode)

Operating mode 0 is just the PRIVATE_MODE. The developer should have used the variable instead of just setting it to zero. Their are multiple modes for the sharedpreference. You can look into the docs for more. Private mode means that this data can be accessed by this application only.

3) How can I add a watch for getSharedPreferences (Where is it stored?)

Not sure what you mean by adding a watch. Are you talking about an event listener on the sharedPreference? AFAIK, you can't do that. Also, shared preference is stored in app's cache directory which can be /data/app/appname/cache or something else (idk for sure)

Answer 2

Shared Preferences store data till you delete and reinstall the app

getBoolean( "this is the key" , true);

if getBoolean returns null then this whole statement evaluates to true

If getBoolean( "this is the key" , false);

This means that if it returns null then evaluate it to false

Meaning why would it return true if it doesn't exist?

This was your question right ?

It is the coder's choice to make it true or false like

At first when user has logged in when you did not even touch sharedPreferences then it would probably return the second argument

like

if(SharedPreferences.getBoolean('isUserOld' , true)){

Toast.make( Context , "Welcome to Our App" , Long).show()


}

Here it is checking whether user is old or not If user is not old then if blocks gets executed because the second param returns true

And this indicates that a new user has logged in