How can i find binder object in a android parcel? i want to marshall a parcel which has got a bitmap but i got Runtime exception says that the parcel has got binder object.
Sadly, you can't. A Parcel is unfortunately sometimes more than just a stream of bytes. Occasionally it contains an intelligent object, called a Binder. These objects can be passed around using IPC and have methods called by different processes in different parts of the Android system.
That's what's happening in this case. When you called Bitmap.writeToParcel() it's putting some intelligent object in there, which needs to be queried by other parts of the OS. That means that this Parcel simply can't be reduced to a stream of bytes.
(Specifically I think what's happening is this - but I could be wrong. I believe that this code:
http://androidxref.com/4.1.1/xref/frameworks/native/libs/binder/Parcel.cpp#736
is writing the bitmap data to an area of shared memory, and putting a reference to that shared memory area into the parcel. This means that the data doesn't need to be copied so often, which is great when you're passing the Parcel to another process using IPC, but not so good if you're just using it to serialize data.)
Using Parcel.marshall sometimes suggests bad design... as the comment says,
The data you retrieve here must not be placed in any kind of persistent storage (on local disk, across a network, etc). For that, you should use standard serialization or another kind of general serialization mechanism. The Parcel marshalled representation is highly optimized for local IPC, and as such does not attempt to maintain compatibility with data created in different versions of the platform.
If you are using it for local IPC, then you shouldn't need to call Parcel.marshall - because normally it would be part of an AIDL interface where these things are handled automatically.
Sorry there's no immediate solution! If you're using it for IPC, then use AIDL. If you're using it for something else, then don't use Parcel.marshall - instead you'll have to go to more effort to write the bitmap bytes to your own data format.
Related
Why does Android use parcels to pass data between components (e.g. two Activities)? Why not just a reference to the object?
Parcel is a container for a message(data and object references). In transmission, Parcel contains a byte stream version of a chosen Java Object that contains information about it's attributes. Such data is written to Parcel at sending component, and is read at receiving component. Because the protocol is also designed to support IPC(Inter-Process Communication), only a reference wouldn't suffice. If you really want to use just a reference you can declare your object containing data public static, although I wouldn't recommend this because of the global scope & tight coupling of components.
If we look at common ways of sharing data between activities, we can make a reasonable guess at why this is the case.
Alternatives include using singletons and SharedPreferences - entities that basically act as "owners" of the state stored by the data. The use of a third party keeps the activities decoupled, as compared to activities simply giving each other references.
We want activities to be decoupled since any two activities should be fairly distinct entities, with possibly independent lifecycles. This is why if we can simply pass information by value (rather than keep a live reference dependency), we should. This is also why it's comparable to Inter-Process Communication, which works around the lack of shared memory.
I want to know exact ,
whether should I used parcelable or serialization technique
for sending data from one activity to other?
is it compulsory to
use one of them for sending data from one to other?
when should I use them?
and the exact difference between them and performance
of both of them in java aspects.
Thanks in advance.
public class GetSetClass implements Serializable {
private int dt = 10;
/** pass any object, drwabale */
public int getDt() {
return dt;
}
public void setDt(int dt) {
this.dt = dt;
}
}
These concepts are related to Inter Process Communication (IPC).
When sending data between two applications, we have to make sure that both applications should understand the format of the data that is being sent.
Especially when you are sending non primitive data type values like classes and objects between two applications, We have to convert them into Operating System understandable format. O.S understands only primitive types (ints, chars etc). The reason for conversion is we have to O.S communication channel to transmit the data.
This process of converting Non primitive types to primitives and sending across to other application over some communication channel is called as Serialization. The reverse process is called as De Serialization.
In Java, IPC depends heavily on Serializables for serialization. But serialization is designed by keep desktop applications in mind. When you are doing IPC in mobile applications we have to make sure that the process of IPC is not too heavy.
In simple terms serialization is a heavy concept for IPC.
So in place of Serialization Android opted for Binders for achieving light weight Inter process communication. Binders internally depends heavily on parcels, to do the IPC.
Parcels are light weight serializables. It is preferred to use parcels for marshaling objects into byte streams.
Note: Binder IPC heavily depends on Shared memory concept to make sure that there is not much data duplication while sharing between applications.
whether should i used parcelable or serialization technique for sending data from one activity to other.
If you are sending a non-primitive type data/Object to another activity through the intent you have to either Serialize or implement Parcelable for that object. The preferred technique is Parcelable since it doesn't impact the performance.
is it compulsory to use one of them for sending data from one to other. / when should i use them.
It is only compulsory/used for sending non-primitive type data objects.
and the exact difference between them and performance of both of them in java aspects.
Serialization does impact the performance. For more details check this link Android Parcelable and Serializable
Got a very good explanation of difference between Parcelable and Serialization.
To start with your question though its been a long time, it may help others:
whether should I used parcelable or serialization technique for sending data from one activity to other?
Ans: Parcelable is best choice (why explained later).
is it compulsory to use one of them for sending data from one to other?
Ans: Yes, as sending data (object) from one to other requires streams of bytes to be written and retrieved and that can be done either through parcelable or serialization.
when should I use them?
Ans: This part you arleady answered i.e, passing data from one activity to another.
and the exact difference between them and performance of both of them in java aspects.
Ans: 1. Parcelable is well documented in the Android SDK; serialization on the other hand is available in Java.
In Parcelable, developers write custom code for marshaling and unmarshaling so it creates less garbage objects in comparison to Serialization. The performance of Parcelable over Serialization dramatically improves (around two times faster), because of this custom implementation.
Serialization is a marker interface, which implies the user cannot marshal the data according to their requirements. In Serialization, a marshaling operation is performed on a Java Virtual Machine (JVM) using the Java reflection API. This helps identify the Java objects member and behavior, but also ends up creating a lot of garbage objects. Due to this, the Serialization process is slow in comparison to Parcelable.
Answer taken from:
this link
See also:serialization explained
Java Serializable:-
Serializable comes from standard Java and is much easier to implement all you need to do is implement the Serializable interface and add override two methods.
The problem with Serializable is that it tries to appropriately handle everything under the sun and uses a lot reflection to make determine the types that are being serialized. So it becomes a beefy Object.
Androids Parcelable:-
Android Inter-Process Communication (AIPC) file to tell Android how is should marshal and unmarshal your object.It is less generic and doesn't use reflection so it should have much less overhead and be a lot faster.
Read More from http://www.3pillarglobal.com/blog/parcelable-vs-java-serialization-android-app-development
both parceling and serializing are ways to marshall and unmarshal data. in android this is used to pass non-primitive data types between components and processes. in general, android allows either serializable or parcelable objects, so you can choose your method. the exception to that is with AIDL interfaces. objects must be parcelable to be passed / returned.
serialization uses reflection to automatically marshall and unmarshal data. in most cases implementing the marker interface is enough to make it just work. with parceling, you have to write the code to marshall and unmarshal the data yourself.
and hence, that is why parceling is faster. the object does not need to be reflected to discover the fields. it's the reflection that makes it slow.
serialization also has in-built versioning ... if you try to unmarshal to a different version of the object's class that was marshalled, the process will fail in a predictable way. with parceling, you can do the same thing but you need to implement it yourself by adding a "version field to your object, and code that checks the version when unmarhsaling.
that being said, i typically use serialization. with simple objects you won't notice the difference. you can always change to use parceling later in development if you discover performance issues.
I know this question has been asked multiple number of times and i have been through a lot of these questions......almost all of these questions throw up the use of the parcelable interface for your class.
However in a couple of questions i came across a quotation:
"NOTE: Seeing Parcelable might have triggered the question, why is Android not using the
built-in Java serialization mechanism? It turns out that the Android team came to the conclusion
that the serialization in Java is far too slow to satisfy Android’s interprocess-communication
requirements. So the team built the Parcelable solution. The Parcelable approach requires
that you explicitly serialize the members of your class, but in the end, you get a much faster
serialization of your objects.
Also realize that Android provides two mechanisms that allow you to pass data to another
process. The first is to pass a bundle to an activity using an intent, and the second is to pass a
Parcelable to a service. These two mechanisms are not interchangeable and should not be
confused. That is, the Parcelable is not meant to be passed to an activity. If you want to start
an activity and pass it some data, use a bundle. Parcelable is meant to be used only as part of
an AIDL definition."
This quote can also be found in the book Pro Android 2.
Now seeing that all activities within the same application run in the same process(Every Activity in Android is a Process,or One Application is one process),unless otherwise specified in the manifest,communication within the activities of the same application is not Interprocess communication per se.So is it really faster to use the parcelable class or is it just enough to pass your object attributes through bundle via intent ?
Shedding any light on this aspect will be largely appreciated.
Cheers !!
There's a FAQ for that. :)
The short answer is that the Android team recommends three techniques for passing data between activities and services within an app: a singleton class; a public static field or method; a HashMap of WeakReferences to Objects (and you pass the key in the intent). The major issue to keep in mind is how your data is going to behave under various lifecycle events. (For instance, if the user turns the phone, by default your activities will be destroyed and recreated; your data handling method needs to be designed with that in mind.)
The Parcelable construct is designed to be very fast at passing data across application memory boundaries: within an application you are MUCH better served using Bundle because all the memory locations the data is stored in are accessible to both the sender and the receiver. Since the in-memory objects are accessible there is no need to incur the cost of reconstruction: just use the Bundle, which is really just a glorified HashMap with type-specific put/get methods.
For AIDL and IPC purposes you can't (by default) share memory locations so you need an efficient way of moving data: this is where Parcelable kicks in. Unless one of the components of your application is using the remote process capability then there is no need to use Parcelable.
From docs:
Parcelables
The Parcelable protocol provides an extremely efficient (but
low-level) protocol for objects to write and read themselves from
Parcels. You can use the direct methods writeParcelable(Parcelable,
int) and readParcelable(ClassLoader) or writeParcelableArray(T[], int)
and readParcelableArray(ClassLoader) to write or read. These methods
write both the class type and its data to the Parcel, allowing that
class to be reconstructed from the appropriate class loader when later
reading.
There are also some methods that provide a more efficient way to work
with Parcelables: writeTypedArray(T[], int), writeTypedList(List),
readTypedArray(T[], Parcelable.Creator) and readTypedList(List,
Parcelable.Creator). These methods do not write the class information
of the original object: instead, the caller of the read function must
know what type to expect and pass in the appropriate
Parcelable.Creator instead to properly construct the new object and
read its data. (To more efficient write and read a single Parceable
object, you can directly call Parcelable.writeToParcel and
Parcelable.Creator.createFromParcel yourself.)
Bundles
A special type-safe container, called Bundle, is available for
key/value maps of heterogeneous values. This has many optimizations
for improved performance when reading and writing data, and its
type-safe API avoids difficult to debug type errors when finally
marshalling the data contents into a Parcel. The methods to use are
writeBundle(Bundle), readBundle(), and readBundle(ClassLoader).
I'm in need to serializing a comprehensive application (game) state to be transmitted over a network or saved to disk and retrieved at a later time.
Bundles, of course, are used to save/restore states in several use cases, so using them would be ideal. However, for some reason, Bundle isn't serializable.
Searching for a solution has only turned up the unacceptable hack of turning the Bundle into a Parcel and then marshalling that, but it is not an acceptable solution because there is no guarantee that it will be possible to unmarshall the data at a later date or on a remote device.
So as it looks now, the only solution appears to be to get the entire set of keys from the Bundle, get each contained Object, do a rather huge switch/case on each Object.Class and manually construct a giant ByteBuffer or similar from all this data, along with size and type information in order to successfully reconstruct the whole thing on the other side.
Not exactly smooth.
Does anyone know of a better way? Perhaps someone has already created a utility function for Bundle that does this?
Great Question! I wonder if you need to serialize the whole bundle or just information contained? Probably you only need the information which you you can save in just any type (String, List or Array). Take a look at the subclasses of java.io.Serializable, which is humongous.
This is a question I've now had for a few different apps I've built, and I have yet to be satisified with any of the solutions I've come up with. I thought I'd put it out there to the community to see other solutions there might be.
Let's say you have an Activity that downloads a complex tree of data (in this case via json, but it could be anything), unmarshalls that data to a set of java objects (in this case using gson, but again, could be whatever), then spawns additional activities to view different parts of that data. There might be one activity to view Trips in your response, and another to view Flights in those trips, and maybe another to view Passengers of those flights.
My initial implementation of this app was to unmarshall all the Trips in the first activity, then pass them by value (as an extra in the intent) to the TripActivity. The TripActivity then passes individual flights to the FlightActivity, and so on.
The problem with this is that there's a noticeable pause between activities while the app serializes and deserializes the data. We're talking several seconds. The pause is quite noticeable when my tree uses Serialization or Parcelable to pass data around. Initial performance testing with using google's Parcelable instead show a roughly 30% speedup over serialization, but Parcelable is difficult to work with and doesn't seem to handle circular object references well like Serialization does, and besides it still pauses for almost as many seconds, so I've put that experiment on the backburner while I try other things.
So then I tried moving the tree of objects directly into the Application class. Each activity just gets the tree directly from the app whenever it needs it. This makes performance quite snappy, but handling corner cases like unexpected activity start/stops (either due to activity crashes or because the activity has been closed temporarily to make more memory available, or whatever other cause) seems tricky. Perhaps it's no more than implementing onSaveInstanceState(), I'm not sure, but the solution seems a bit hacky so I haven't investigated further yet.
So in search of a less cobbled-together solution, I tried creating a custom ContentProvider to store and retrieve my objects. Since ContentProviders can be configured to run in-process using multiprocess=true, I thought that would be an excellent way to avoid serialization costs while doing something more "standard" than storing data in the Application object. However, ContentProviders were clearly not intended to return arbitrary object types -- they only support types such as numbers, strings, booleans, etc. It appears I can finagle one to store arbitrary objects by using ContentResolver.getContentProviderClient().getLocalContentProvider() and accessing my custom class directly, but I'm not sure that's less hacky than storing data in the Application object.
Surely someone must have a good solution to this problem. What am I doing wrong?
In addition to fiXedd's solution, another one is to use a local service. Have the service "own" the objects, with activities calling service APIs to get whatever it needs. The service can also be responsible for fetching and parsing the data, encapsulating that bit of logic.
The Application object is the "red-headed step-child" of Android components. Members of the core Android team have come out against the practice of creating custom Application subclasses, though it is certainly supported by the API. Having engineered one ADC2 200 application that leveraged a custom Application subclass, I can say that I should have gone with a service in my case as well. Live and learn...
By using the local binding pattern, your service will automatically be created and destroyed as needed, so you don't have to worry about that. And, by definition, a local service runs in the same process/VM as your activities, so you don't have to worry about marshaling overhead like you would in the ContentProvider scenario.
The way I'm handling this in one of my apps is downloading the data then shoving it into a database. This way I don't have to carry all those objects around (which, IIRC, eat about 1kb each just for the object instantiation) and I can easily pull just the data that I need. I don't know if this will work for you, but it worked for my use-case.
Another approach would be to save the data objects to a shared preferences file. That's how we implemented one of our apps, but I didn't like that approach because it seems too slow.
It's bad coding practice, but the fastest way may be to just use a service to parse the data and save the data to a static class that you can use for the rest of the app's life.