MyAndroidSchool

I will be pushing all the android applications I develop as a part of pursuing the Android starter course with Kotlin in Udacity and the Kotlin android fundamentals codelab

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Random notes :)

Activities

• An activity represents a single screen in your app with an interface the user can interact with.

Intents

• Each activity is started or activated with an Intent, which is a message object that makes a request to the Android runtime to start an activity or other app component in your app or in some other app.
• In addition to simply starting one Activity from another Activity, you also use an Intent to pass information from one Activity to another.
• Intents can be explicit or implicit:

• Implicit: You do not specify a class to recieve the intent. Instead, you declare a general action to perform, and the Android system matches your request to an activity/other component that can handle the requested action.
• Explicit: You specify the receiving activity (or other component) using the activity's fully qualified class name.

• To get data back from a launched Activity, start that Activity with the startActivityForResult() method instead of startActivity()
• Call finish() to close the Activity and resume the originating Activity

Broadcast

Broadcasts are messages that the Android system and Android apps send when events occur.

• System broadcasts are delivered by the system.
• Custom broadcasts are delivered by your app.

System broadcasts

• A system broadcast is a message that the Android system sends when a system event occurs.
• System broadcasts are wrapped in Intent objects.

Examples:

• When the device boots, the system broadcasts a system Intent with the action ACTION_BOOT_COMPLETED
• When the device is disconnected from external power, the system sends a system Intent with the action field ACTION_POWER_DISCONNECTED.

Custom broadcasts

• Custom broadcasts are broadcasts that your app sends out.
• Use a custom broadcast when you want your app to take an action without launching an activity.
• To create a custom broadcast, define a custom Intent action.

There are three ways to deliver a custom broadcast:

1. For a normal broadcast, pass the intent to sendBroadcast().

• The sendBroadcast() method sends broadcasts to all the registered receivers at the same time, in an undefined order.
• Most efficient way to send a broadcast

2. For an ordered broadcast, pass the intent to sendOrderedBroadcast()

To send a broadcast to one receiver at a time, use the sendOrderedBroadcast() method:

• The android:priority attribute that's specified in the intent filter determines the order in which the broadcast is sent.
• If more than one receiver with same priority is present, the sending order is random.
• The Intent is propagated from one receiver to the next.
• During its turn, a receiver can update the Intent, or it can cancel the broadcast. (If the receiver cancels the broadcast, the Intent can't be propagated further.)

3. For a local broadcast, pass the intent to LocalBroadcastManager.sendBroadcast().

• Sends broadcasts to receivers within your app.
• This method is efficient, because it doesn't involve interprocess communication.
• Also, using local broadcasts protects your app against some security issues

Click here for broadcast methods in java

Broadcast receivers

• Broadcast receivers are app components that can register for system events or app events.
• When an event occurs, registered broadcast receivers are notified via an Intent.

Use broadcast receivers to respond to messages that have been broadcast from apps or from the Android system. To create a broadcast receiver:

1. Define a subclass of the BroadcastReceiver class and implement the onReceive() method.
2. Register the broadcast receiver, either statically or dynamically.