[android] What is a "bundle" in an Android application

What is a bundle in an Android application? When to use it?

Pass data between activities by using Bundle and Intent objects.

Your first create a Bundle object

Bundle b = new Bundle();

Then, associate the string data stored in anystring with bundle key "myname"

b.putString("myname", anystring);

Now, create an Intent object

Intent in = new Intent(getApplicationContext(), secondActivity.class);

Pass bundle object b to the intent

in.putExtras(b);

and start second activity

startActivity(in);

In the second activity, we have to access the data passed from the first activity

Intent in = getIntent();

Now, you need to get the data from the bundle

Bundle b = in.getExtras();

Finally, get the value of the string data associated with key named "myname"

String s = b.getString("myname");

Bundle is used to pass data between Activities. You can create a bundle, pass it to Intent that starts the activity which then can be used from the destination activity.

First activity:

String food = (String)((Spinner)findViewById(R.id.food)).getSelectedItem();
RadioButton rb = (RadioButton) findViewById(R.id.rb);
Intent i = new Intent(this,secondActivity.class);
i.putExtra("food",food);
i.putExtra("rb",rb.isChecked());

Second activity:

String food = getIntent().getExtras().getString("food");
Boolean rb = getIntent().getExtras().getBoolean("rb");

Bundle:- A mapping from String values to various Parcelable types.

Bundle is generally used for passing data between various activities of android.

when we call onPause() then onStop() and then in reverse order onStop() to onPause().

The saved data that the system uses to restore the previous state is called the "instance state" and is a collection of key-value pairs stored in a Bundle object.

Bundle is not only to transfer data between two different components but more importantly it is used to restore the values stored before activity is destroyed into new activity.

such as the text in an EditText widget or the scroll position of a ListView.

I have to add that bundles are used by activities to pass data to themselves in the future.

When the screen rotates, or when another activity is started, the method protected void onSaveInstanceState(Bundle outState) is invoked, and the activity is destroyed. Later, another instance of the activity is created, and public void onCreate(Bundle savedInstanceState) is called. When the first instance of activity is created, the bundle is null; and if the bundle is not null, the activity continues some business started by its predecessor.

Android automatically saves the text in text fields, but it does not save everything, and subtle bugs sometimes appear.

The most common anti-pattern, though, is assuming that onCreate() does just initialization. It is wrong, because it also must restore the state.

There is an option to disable this "re-create activity on rotation" behavior, but it will not prevent restart-related bugs, it will just make them more difficult to mention.

Note also that the only method whose call is guaranteed when the activity is going to be destroyed is onPause(). (See the activity life cycle graph in the docs.)

bundle is used to share data between activities , and to save state of app in oncreate() method so that app will come to know where it was stopped ... I hope it helps :)

use of bundle send data from one activity to another activity with the help of intent object; Bundle hold the data that can be any type.

Now I tell that how to create bundle passing data between two activity.

Step 1: On First activity

Bundle b=new Bundle();

b.putString("mkv",anystring);

Intent in=new Intent(getApplicationContext(),secondActivity.class);

in.putExtras(b);

startActivity(in);

Step 2: On Second Activity

Intent in=getIntent();

Bundle b=in.getExtras();

String s=b.getString("mkv");

I think this is useful for you...........

Just create a bundle,

Bundle simple_bundle=new Bundle();
simple_bundle.putString("item1","value1");
Intent i=new Intent(getApplicationContext(),this_is_the_next_class.class);
i.putExtras(simple_bundle);
startActivity(i);

IN the "this_is_the_next_class.class"

You can retrieve the items like this.

Intent receive_i=getIntent();
Bundle my_bundle_received=receive_i.getExtras();
my_bundle_received.get("item1");
Log.d("Value","--"+my_bundle_received.get("item1").toString);

Bundles can be used to send arbitrary data from one activity to another by way of Intents. When you broadcast an Intent, interested Activities (and other BroadcastRecievers) will be notified of this. An intent can contain a Bundle so that you can send extra data along with the Intent.

Bundles are key-value mappings, so in a way they are like a Hash, but they are not strictly limited to a single String / Foo object mapping. Note that only certain data types are considered "Parcelable" and they are explicitly spelled out in the Bundle API.

A Bundle is very much like a Java Map object that maps String keys to values. It's used to pass information between activities and other application components. It's also used by the framework to capture and restore state information.

The reason Android doesn't use plain old Map objects for this is that Map is too flexible; it can contain objects (such as, say, I/O streams) that cannot be serialized. The Bundle API restricts the types of objects that can be added to a bundle in such a way that the bundle's contents are guaranteed to be serializable. The Android framework relies on this property.

I suggest that you read the documentation on Application Fundamentals. This explains, among other things, what bundles and intents are and what they are used for.