Lecture 4 Handling Runtime Changes and Intents

8/13/2019 Lecture 4 Handling Runtime Changes and Intents

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Lecture 4HANDLING RUNTIME CHANGES AND INTENTS


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Handling Runtime Changes

Saving StateUsing onSaveInstanceState & onRestoreInstanceState

Retain an object during a configuration change

Using onRetainNonConfigurationInstance() & getLastNonConfigurationInstance(

Handle the configuration change yourself

Prevent the system from restarting your Activity


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Method 1 : SavingState


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Saving Application State : Saveprotected void onSaveInstanceState (Bundle outState)

{

// TODO Auto-generated method stub

super.onSaveInstanceState(outState);

outState.putInt("color", Color.GREEN);

}


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Saving Application State Restore@Override

protected void onRestoreInstanceState(Bundle savedInstanceState)

{

// TODO Auto-generated method stub

super.onRestoreInstanceState(savedInstanceState);

int color = savedInstanceState.getInt("color");

//myWidget.setBackgroundColor(color);

}


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Saving State and BundlesOverriding the onSaveInstanceState and onRestoreInstanceState

save and restore the application state after restart.

E.g. when the screen rotates. Not when using the back key


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Saving State Notes Called by default for all widgets

Text in EditText and CheckBox state are saved automatically but you have to make

you should always call the superclass implementation

You should NOT use saveInstanceState for persistence purposes


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Method 2 : Retain anobject


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Retaining a stateful ObjectImplement onRetainNonConfigurationInstance()

to return an object carrying your data and then retrieve the data

when your Activity starts again with getLastNonConfigurationInstance()

For example:


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Method 3 : Handling configurations changesAndroid


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Handling configurations changes byAndroid

You can stop activity from being restarted by adding the following in the manifeast


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Handing runtime changes referehttp://static.meizu.com/m9sdk/guide/topics/resources/runtime -changes.html


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Intents


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What is an intent An intent is an abstract description of an operation to be performed

It can be used to

Start another activity, using startActivity()

Broadcast a message to interested broadcast receivers, using sendBroadCast()

Starting a service, using startService() or bindService()


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Intents: starting another activityIntent myAct2 = new Intent(this,MyActivity2.class);

startActivity(myAct2);

The manifest file needs to know about the activity

Add this entry inside the application element


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Implicit and explicit intentsExplicit intents

designate the target component by its name

Implicit intents

do not name a target. Implicit intents are often used to activate components in otapplications.


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Intent StructureAction -- The general action to be performed, such as

ACTION_VIEW

ACTION_EDIT

ACTION_MAIN

Data -- The data to operate on, such as a person record in the contacts database, ea Uri.

E.g. Open contact from contacts named John Steve

Intent with ACTION_VIEW and data name of contact


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Intent Example : View Contact(s)


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Examples of Data/Action Pairs


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ExerciseMake an application that takes a phone number as input and click a button to call.

immediately, do not show the dialer


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Intents Secondary Attributes (coCategory

Categories provide additional detail about the action the intent is perform

When resolving an intent, only activities that provide all of the requested categoriused.

Components

Components classes (optional). explicit name of a component class to handle the

TypesTypes of data/message related to the intents as we saw in previous examples

Extras

Extra information needed for handling the intent by the intent receiver


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Intents ExamplesSome times the action/data pairs are not enough information to the activity. E.g. s

Action : SendSMS

Data : to whom

What about the message itself ?

Thats why there are Secondary attributes.


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Intents Examples (cont.)Show images


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Intents Examples (cont.)Launching Music Player


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Intents Examples (cont.)Play Music File


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Intents Examples (cont.)Sending MMS


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Intents Examples (cont.)Sending Mails

Intent sendMail = new Intent(Intent.ACTION_SEND);


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Assignment : Email Sender

Documents

Lecture 4 Handling Runtime Changes and Intents