I want to share object from one activity to another activity. I know of 2 good ways:
Using bundle: By making object's class implement Parcelable, can pass object in bundle via intent.
Using singleton pattern: saving the object instance in this class and then fetch it where ever required.
Which of the above mentioned is better or recommended way? Kindly also tell if there is some other better way.
Singleton isn't a good ideia on Activities, because it will produce memory leak (redundancy of information of an Activity).
Parcelable it's a good idea, because you will not use disk IO or Network when you create a local object from a form in the first Activity.
If you retrieve an object from Network or local database, you don't need anyone, because you can retrieve the object in the next Activity.
Related
The only way that I see is to use a static variable, but it's not okay as I want to keep the ability to start multiple Activites.
In my case, I want to keep a reference of Dagger 2 Component.
It will provide objects like Navigator. I can't just store it into Bundle.
For now, I can't use Retain MainFragment instead of MainActivity because of this bug.(I'm at 23 API level)
Is there any Retain Activity implementation?
Huh, well you have two built in solutions in android to fix this problem:
1) If the object is serializeable or parcelable you can override onSaveInstanceState() and read the value out in onCreate. Here are the google developer docs for the specifics on that.
2) If your object is not serializable you can instead override onRetainNonConfigurationInstance() and return that object. You can then get the object back in onCreate. Look at this SO post for how to use this approach (don't persist your activity though! persist the object.). The drawback of this is that you can only persist one object at a time.
I have a more in depth write up of these two approaches and third, declarative approach that you can roll. It relies on onRetainNonConfigurationInstance and allows you to use annotations to declare what variables in your activity should be persisted. check it out here. That said, I wouldn't recommend using this unless you have more than one non-serializeable/parcelable object to persist.
Edit: clarified point that you shouldn't persist your whole activity using onRetainNonConfigurationInstance().
I am quite new in Android. So, please help me this question.
I have Fragment which I show to user an Email. I put the email content to a Model Object.
Should I put the model object to the bundle in onSaveInstanceState method or how can I persist the model object for Fragment recreate ?
Maybe it is a simple question but please help me.
If you want to save the object in a bundle, it should be a parcelable object. You can use putParcelable and getParcelable for saving and restoring object. Usually it's discouraged to save large data since it will make recreation slower. Only save what you absolutely need.
I'm on the situation where I have to share variables between activities... but I have one doubt. Which is better: Parcelable object or set it on a custom Application object.
When something is just going to be used in next activity I just pass it as a Parcelable object, and when it is going to be used in more than one activity, I put it on Application context.
What do you think? Is it right? Which is better in performance?
Thanks!
I think your approach is completely valid.
If it is something like a user object that is accessed in every Activity store it in a custom Application object, but be sure to have a way to recreate the object if the application object gets destroyed while the app is in background.
If it is something like a path or a choice the user made that determines how the next activity works send it with the Intent.
There are also some classes that are not easy to put in an Intent. I have an ImageCache that is attached to the application class that allows to keep images like a user profil image in memory between activity changes without the need to decode the bitmap multiple times. If they are designed in a way that they don't fill up all available memory those are also a good fit for a custom app class.
I recommend sharing data between activies with extras. If it's a own class, it must implement Serializible.
If you are feeling lazy, go with Application's singleton pattern.
But, if you want to code smarter, go with Parcelable.
How do you pass an instance of ArrayList<ArrayList<HashMap<String, String>>> from one Android activity to another via an instance of Bundle?
(I could use JSON strings. I'd like to know if there are better ways.)
Thanking you kindly in advance.
You can pass it as an extra in the Intent that you use to fire up the new activity. Since ArrayList implements Serializable, you don't have to do anything special to feed it to Intent.putExtra().
In general it is not good to pass too many or too large data between activities via Intents. It's better to store them somewhere centrally and pass a lightweight identifier or something like this, so the other activity can retrieve them from the store.
E.g. you can use an Application class to store these data. An application class is always available as long as you application is running. You get it from each Activity by calling the getApplication() method.
I have read some question here but I didn't find a solution. I have read about Parcelable, Intents, and sharing specific data within Activities from the android dev docs (both dev guide and reference).
Here's the scenario:
I have one ListActivity that fills in an object parsing an xml file, it shows a list of values, and when clicked I want to return the object that represents the item clicked to the activity that has called it, for then, call another activity with this object.
I read on how to implement Parcelable but seems not being the way. Implementing Parcelable receives a Parcel for the constructor and then reads the values from it (or at least that was what I understood). This makes no sense for me and I can't see how to implement basing on that issue. I build the object parsing the xml file, not having a Parcel.
I appreciate some clarifications on this, regards.
I believe you have three options here:
Pass some arbitrary 'id' of the object to the new activity in the intent extras, which obtains the object in the same way as the first activity. This I would recommend as it is in harmony with the way Android is designed to work.
Serialize the object using Java Serializable, then put it into the intent as an extra.
Have the object be a JSONObject and send it as a string in the intent extras.
That depends on whether the activities belong to the same process or different ones...if it is the same process then the answer is Within an application what is the best way to pass custom objects between activities? but if they belong to different processes then you are better of implementing parcelable.