Android：intent.putExtra（）会更改对象吗？

Question

I want to pass myObject to the NewActivity class. For this I use the putExtra() and getExtras() methods from Intent . It appears however that the object changes somehow? I'm printing the object both before and after I pass it.

Is this normal? I'm running into problems because I'm using myObject in a HashMap, and since the object in NewActivity is essentially an entirely different object I can't use it as a key anymore.

Passing the object:

Intent myIntent = new Intent(context, NewActivity.class);
MyClass myObject = new MyClass();
myIntent.putExtra("test", myObject);
System.out.println("OBJECT BEFORE: " + myObject);

Retrieving the object:

MyClass myObject = (MyClass) getIntent().getExtras().getSerializable("test");
System.out.println("OBJECT AFTER: " + myObject);

The (different) prints:

I/System.out: OBJECT BEFORE: my.project.MyClass@8fe5ae4
I/System.out: OBJECT AFTER: my.project.MyClass@9f1fb7b

Answer 1

change this

getIntent().getExtras().getSerializable()

to

getIntent().getSerializableExtra("test")

Answer 2

Serializing and de-serializing does create new objects.

If that's an issue for you because you use it as a key into a HashMap , you should implement the boolean equals(Object other) and the int hashCode() methods in your class.

Check out Java hashCode() on Wikipedia and public int hashCode() in Oracle's documentation to learn how to implement a "hashable" object.

If your object doesn't depend on identity anymore when being used as a key your problem should be solved.

Answer 3

That is how Serializable objects work. 100% basic Java.

They serialize objects into raw data, and then when they're un-serialized, it will create a completely new object of the same type, and set all the values that the old object had onto the new one.

So the object references won't be the same, which is also why a different hashCode is printed out when you call System.out.println .

The internal values of the object will be the same.

Answer 4

For passing object one activity to another, Your object class should implement "Serializable".

public class MyClass implements Serializable{
// 
}

pass data

Intent myIntent = new Intent(context, NewActivity.class);
MyClass myObject = new MyClass();
myIntent.putExtra("test", myObject);

Retrieve data

MyClass myObject = (MyClass) getIntent().getSerializable("test");

Hope this will work :)