If i have an object form interface in my class, how i can pass it to activity?
My solution was to change it as static object, it's work fine but sometimes it create a memory leaks because of all the old references which the garbage collector cannot collect, and i cannot implement 'Serializable' on my interface.
public class MyClass {
protected OnStringSetListener onstringPicked;
public interface OnStringSetListener {
void OnStringSet(String path);
}
//......//
public void startActivity(){
Intent intent=new Intent(context,Secound.class);
// ?! intent.putExtra("TAG", inter);
context.startActivity(intent);
}
}
In my opinion, using Bundles would be a nice choice. Actually bundles internally use Parcelables. So, this approach would be a good way to go with.
Suppose you would like to pass an object of type class MyClass to another Activity, all you need is adding two methods for compressing/uncompressing to/from a bundle.
To Bundle:
public Bundle toBundle(){
Bundle bundle = new Bundle();
// Add the class properties to the bundle
return bundle;
}
From Bundle:
public static MyClass fromBundle(Bundle bundle){
MyClass obj = new MyClass();
// populate properties here
return obj;
}
Note: Then you can simply pass bundles to another activities using putExtra. Note that handling bundles is much simpler than Parcelables.
Passing in custom objects is a little more complicated. You could just mark the class as Serializable
and let Java take care of this. However, on the android, there is a serious performance hit that comes with using Serializable. The solution is to use Parcelable.
Extra info
Related
How to pass origin object from one activity to another on Android?
For sure, we can serialized (Serializable, Parcelable, to/from JSON) and pass a copy of the object's data and a new object having the same data could be created; but it will NOT have the same references.
Here is some solution:
Code for the first activity:
final Object objSent = new Object();
final Bundle bundle = new Bundle();
bundle.putBinder(OBJECT_KEY, new ObjectWrapperForBinder(objSent));
startActivity(new Intent(this, SecondActivity.class).putExtras(bundle));
Code for the second activity:
final Object objReceived = ((ObjectWrapperForBinder)getIntent().getExtras().getBinder(OBJECT_KEY)).getData();
but the minimum API Level required 18
Are there other ways?
SOLUTION:
BundleCompat allows to use putBinder/getBinder for all Android versions.
ActivityA:
final Bundle bundle = new Bundle();
BundleCompat.putBinder(bundle,KEY, new ObjectWrapperForBinder(callback));
intent.putExtras(bundle);
ActivityB:
object = ((ObjectWrapperForBinder)BundleCompat.getBinder(intent.getExtras(),KEY)).getData();
It depends on your goals.
If you're going to work inside one process, you can just simply use Singleton pattern.
But if you want to pass your real object to, for example Service, which has attribute android:isolatedProcess="true" :
<service
android:name=".service.SomeService"
android:enabled="true"
android:exported="false"
android:isolatedProcess="true"/>
Then you can't pass your origin object to another process.
You can't. Apps in one process cannot hold objects from another
process, let alone "invoke operations" upon them.
Source: Passing Objects in IPC using Messenger in Android
So, as I can see you are're trying to pass your origin object using Intent mechanism. In my opinion, it's impossible to do it through the Intent's, because Bundle, which contained in Intent doesn't store references to real objects. So, it's impossible.
In such case,EventBus will be a great choice.It's something like global Subscribe-Observer and it can help to pass origin object between any objects.
Do this in the activity where you want to pass an object:
EventBus.getDefault().register(this);
EventBus.getDefault().post(new MessageEvent());
Do this in the activity where you want to receive the object:
First,register the activity:
EventBus.getDefault().register(this);
Second,define an method with #Subscriber to receive the object:
#Subscribe
public void onMessageEvent(MessageEvent event)
Hope this will help.
Sample object should be Parcelable.
SampleObject objSent=new SampleObject();
Intent intent=new Intent(mContext,NewActivity.class);
intent.putExtra(objSent);
startActivity(intent);
I want to pass a data object to Fragment, here are two ways to do this:
public class MyFragment extends Fragment {
private Serializable way1;
private Serializable way2;
public void setDataWay1(Serializable way1) {
this.way1 = way1;
}
public void setDataWay2(Serializable way2) {
Bundle data = new Bundle();
data.putSerializable("data", way2);
setArguments(data);
}
}
So, what is the difference between the 2 ways? Sometimes, way1 may cause NullPointerException,why? If I want to pass a OnClickListener to Fragment, what should I do?
While both methods can set the appropriate data to your fragment for first time initialization. Note that fragments will be recreated and destroyed by the system (for example on screen rotation). When that happens the system will not really call the setter way (method 1) hence, it will be a giant FAIL. Therefore, it is recommended to use the setArguments() way.
I have a data of custom List type (finalHolder.data)
Earlier I had to send this data to a Fragment constructor it is working fine
Fragment fragment;
fragment = new RouteMap(finalHolder.data);
((Activity)getContext()).getFragmentManager().beginTransaction().replace(R.id.content_frame,fragment).commit();
The Fragment constructor code
public RouteMap() {
// Required empty public constructor
}
public RouteMap(MyListEntity data) {
this.data = data;
}
Activity constructor :
public Map() {
}
public Map(MyListEntity data) {
this.data = data;
}
But now I want this same data to reach a Activity (Map2)
I tried putExtra with intent but Intent but it doesnt work
In Short I want the "finalHolder.data" to be send to Activity constructor while calling it .
If it isnt possible then please suggest solution
Thanks
It is not recommended to use Activity constructor. To send data object to activity you can use Intent extras with Parcelable. For that you need to do the follow way.
Implement your data class from Parcelable
Ex: MyListEntity implements Parcelable
Override the following methods in your data class(MyListEntity) writeToParcel(), readFromParcel()
3.Implement the CREATOR class in your data class(MyListEntity)
Reference link for Parcelable example: passing object to activity
Send the data object using Intent as mentioned below
Intent i = new Intent(this,Activity(Map2).class);
i.putExtra("mylistdata",finalHolder.data);
startActivity(i);
And finally get the same data at your Activity(Map2) onCreate() method as mentioned below
MyListEntity listEntry = getIntent().getParcelableExtra("mylistdata");
Now your object is ready at your second activity.
Hope this will help for you.
To send an object in intent the object's class must be serializable so make your
MyListEntity implements serializable then use the Intent's putExtra(String name, Serializable value) and in the other activity use the intent's getSerializableExtra (String name) but don't forget to cast the returned value
One option could be letting your custom class implement the Serializable interface and then you can pass object instances in the intent extra using the putExtra(Serializable..) variant of the Intent#putExtra() method.
Your data should implement Serializable ie
MyListEntity implements Serializable
//Use this to send the data
intent.putExtra("MyClass", finalHolder.data);
// To retrieve object in second Activity
getIntent().getSerializableExtra("MyClass");
Regarding your Fragment: it is not smart to pass data via c-tor to fragments!
Use arguments mechanism:
Fragment f = new SomeFragment();
Bundle args = new Bundle();
args.putExtra("data", someData);
f.setArguments(args);
And retreive them:
getArguments().getParcelableExtra("data")
More info here.
But (to return to your question), for that, your data have to implement Serialisable (Java approach) or, by Google advised Parcelable (Android style)
More info about Parcelable here.
Implementing Parcelable interface can be boring and error prone, so some cool people created this: http://www.parcelabler.com/
I am trying to pass an object from an activity to another activity. Here is what i do:
MyApplication.db= dbToOpen;
Intent i = new Intent(mContext, OpenDbActivity.class);
i.putExtra("PARENT_GROUP", dbToOpen.root);
mContext.startActivity(i);
Here, MyApplication is the class that extends application, and db object is a static object. My extra object dbToOpen.root is an object of the class DBGroupv1.
Then i get this extra in onCreate method of OpenDbActivity class:
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_opendb);
db = MyApplication.db;
groupToOpen = (DBGroupv1) getIntent().getSerializableExtra("PARENT_GROUP");
}
Then i try this boolean expression:
MyApplication.db.root == groupToOpen
and it returns false. When i look at the objects dbToOpen.root and groupToOpen, every single value of the variables inside those objects are the same. But they are are different objects. Why is this happening? Is it because of casting, or does Intent.putextra() method passes a copy of an object, not a reference? If that is the case how can i pass the object as a reference?(Except using static variables)
Thanks
You should use the .equals()-method to compare instances of objects. if you use == you will only get true if the two objects are exactly the same reference. Since the instance in your intent is newly created when deserialized from the bundle, it is no longer a reference to the same instance (although the two objects contains the same data).
So, instead of
MyApplication.db.root == groupToOpen //bad
use
MyApplication.db.root.equals(groupToOpen) //good
Also make sure that if you made the root-object, you implement the equals method properly, so it takes all appropriate variables into consideration.
You can read a bit more here: What is the difference between == vs equals() in Java?
According to what i have learnt from passing data using Intents is that when you pass Object O from Activity A to Activity B via intents, activity B receives a COPY of object O. The way things work is that The object O gets serialized (converted to a sequence of bytes) and that sequence of bytes is then passed to Activity B. Then activity B recreates a copy of object O at the moment it was serialized.
I would like to know if it would be efficient if one extends the Intent class to create a custom Intent and have references to the objects that are required by the other activities and pass the data to the other activities. For example:
public class CustomIntent extends Intent {
private Object o;
public CustomIntent() {
super();
// TODO Auto-generated constructor stub
}
public Object getObject () {
return o;
}
public void setObject(Object object) {
this.o = object;
}
}
In the receiving activity i get the intent and cast the intent to the CustomIntent type and retrieve the object required by the activity. Would this improve the efficiency by reducing the need for Serialization? Kindly throw some light on this. Thanks in advance.
No. Intents are dispatched by the Android system and are always serialized as they can be sent to any activity, service, etc in the system.
For your problem you could probably workaround this issue by creating an Application class and storing your data in it:
class CustomApplication extends Application {
private Object data;
public Object getData() {
return data;
}
public void setData(Object data) {
this.data = data;
}
}
You activate it by updating AndroindManifest.xml setting the android:name property on the application tag you your class name.
To use in your activities:
CustomApplication app = (CustomApplication) getApplicationContext();
app.setData(yourDataObject);
I think it would be better if you let the android handle everything for you. Do not customize it, if it is not very essential.
If you want to have the reference of the object in another activity then there are other ways too.
You can make your object static and directly access it from other activity.
You can make a new object of same type and replace it after coming again back to the first activity(in onActivitResult() method.).
or there may be many more ways to do it.
Thanks.