[android] What's the difference between commit() and apply() in SharedPreferences

I am using SharedPreferences in my android app. I am using both commit() and apply() method from shared preference. When I use AVD 2.3 it shows no error, but when I run the code in AVD 2.1, apply() method shows error.

So what's the difference between these two? And by using only commit() can I store the preference value without any problem?

tl;dr:

• commit() writes the data synchronously (blocking the thread its called from). It then informs you about the success of the operation.
• apply() schedules the data to be written asynchronously. It does not inform you about the success of the operation.
• If you save with apply() and immediately read via any getX-method, the new value will be returned!
• If you called apply() at some point and it's still executing, any calls to commit() will block until all past apply-calls and the current commit-call are finished.

More in-depth information from the SharedPreferences.Editor Documentation:

Unlike commit(), which writes its preferences out to persistent storage synchronously, apply() commits its changes to the in-memory SharedPreferences immediately but starts an asynchronous commit to disk and you won't be notified of any failures. If another editor on this SharedPreferences does a regular commit() while a apply() is still outstanding, the commit() will block until all async commits are completed as well as the commit itself.

As SharedPreferences instances are singletons within a process, it's safe to replace any instance of commit() with apply() if you were already ignoring the return value.

The SharedPreferences.Editor interface isn't expected to be implemented directly. However, if you previously did implement it and are now getting errors about missing apply(), you can simply call commit() from apply().

• commit() is synchronously, apply() is asynchronous

• apply() is void function.

• commit() returns true if the new values were successfully written to persistent storage.

• apply() guarantees complete before switching states , you don't need to worry about Android component lifecycles

If you dont use value returned from commit() and you're using commit() from main thread, use apply() instead of commit()

The difference between commit() and apply()

We might be confused by those two terms, when we are using SharedPreference. Basically they are probably the same, so let’s clarify the differences of commit() and apply().

1.Return value:

apply() commits without returning a boolean indicating success or failure. commit() returns true if the save works, false otherwise.

2. Speed:

apply() is faster. commit() is slower.

3. Asynchronous v.s. Synchronous:

apply(): Asynchronous commit(): Synchronous

4. Atomic:

apply(): atomic commit(): atomic

5. Error notification:

apply(): No commit(): Yes

commit() writes the data synchronously and returns a boolean value of success or failure depending on the result immediately.

apply() is asynchronous and it won’t return any boolean response. Also if there is an apply() outstanding and we perform another commit(). The commit() will be blocked until the apply() is not completed.

The docs give a pretty good explanation of the difference between apply() and commit():

Unlike commit(), which writes its preferences out to persistent storage synchronously, apply() commits its changes to the in-memory SharedPreferences immediately but starts an asynchronous commit to disk and you won't be notified of any failures. If another editor on this SharedPreferences does a regular commit() while a apply() is still outstanding, the commit() will block until all async commits are completed as well as the commit itself. As SharedPreferences instances are singletons within a process, it's safe to replace any instance of commit() with apply() if you were already ignoring the return value.

Use apply().

It writes the changes to the RAM immediately and waits and writes it to the internal storage(the actual preference file) after. Commit writes the changes synchronously and directly to the file.

I'm experiencing some problems using apply() instead commit(). As stated before in other responses, the apply() is asynchronous. I'm getting the problem that the changes formed to a "string set" preference are never written to the persistent memory.

It happens if you "force detention" of the program or, in the ROM that I have installed on my device with Android 4.1, when the process is killed by the system due to memory necessities.

I recommend to use "commit()" instead "apply()" if you want your preferences alive.

From javadoc:

Unlike commit(), which writes its preferences out to persistent storage synchronously, apply() commits its changes to the in-memory SharedPreferences immediately but starts an asynchronous commit to disk and you won't be notified of any failures. If another editor on this SharedPreferences does a regular commit() while a > apply() is still outstanding, the commit() will block until all async commits are completed as well as the commit itself