Lifecycle of Android Services
Lifecycle of Android Services
An Android activity is a component of an application that represents a single screen with a user interface. Activities in Android are responsible for managing the user interface 
and responding to user interactions, such as button clicks, swipes, and other touch gestures. Each activity has a lifecycle that allows it to be created, started, paused, resumed, stopped, and destroyed as needed.
Activities can be launched by other activities, by the system, or by other applications. When a new activity is launched, it is placed on top of the current activity stack and becomes the active activity. The previous activity is then pushed down the stack, and its state is saved so that it can be restored later if needed.
Activities can communicate with each other using intents, which are messages that request an action to be performed. Intents can be used to start a new activity, pass data between activities, or start a service or broadcast receiver.
In summary, activities are the basic building blocks of an Android application, responsible for managing the user interface and handling user interactions. They are essential for creating engaging and interactive mobile applications.
The concept of android activity
An Android activity is a key component of an Android application that represents a single screen with a user interface. Activities are responsible for managing the user interface and responding 
to user interactions, such as button clicks, swipes, and other touch gestures.
Each activity has a lifecycle that defines how it is created, started, paused, resumed, stopped, and destroyed. The lifecycle methods of an activity allow it to save and restore its state, handle configuration changes, and manage its interaction with other activities and the Android system.
Activities are typically defined in the AndroidManifest.xml file and can be launched by other activities, by the system, or by other applications. When a new activity is launched, it is placed on top of the current activity stack and becomes the active activity. The previous activity is then pushed down the stack, and its state is saved so that it can be restored later if needed.
Activities can communicate with each other using intents, which are messages that request an action to be performed. Intents can be used to start a new activity, pass data between activities, or start a service or broadcast receiver.
In summary, activities are essential components of an Android application that allow developers to create engaging and interactive mobile applications with a user-friendly interface. They play a crucial role in managing the user interface, responding to user interactions, and communicating with other activities and the Android system.
Configuring the manifest in android app
The AndroidManifest.xml file is an important configuration file in an Android app that describes the app’s components and their characteristics. It includes information about the app’s activities, services, broadcast receivers, and permissions.
To configure the manifest in an Android app, follow these steps:
- Open the AndroidManifest.xml file in your Android Studio project.
- Define the app’s package name. This should be unique to your app and follow the Java package naming conventions.
- Define the app’s minimum and target SDK versions. This specifies the minimum version of Android that the app supports and the target version that it is designed for.
- Declare the app’s activities, services, and broadcast receivers. Each component must have a unique name, a label for display purposes, and an intent filter that describes the types of intents it can handle.
- Define the app’s permissions. Permissions are used to control access to sensitive system resources, such as the camera or microphone. You must declare any permissions that your app requires in the manifest.
- Configure the app’s icon and label. These are used to identify the app in the launcher and in other parts of the system.
- Define any app-wide settings or features, such as hardware requirements or the app’s theme.
- Save the manifest file and rebuild the app to apply the changes.
In summary, configuring the manifest in an Android app involves defining the app’s package name, SDK versions, components, permissions, icon, label, and other settings. It is an essential step in the app development process and helps ensure that the app functions correctly and meets the necessary requirements.
Declare activities in android with code implementation:
1. Create a new Java class that extends the Activity class. For example:
public class MainActivity extends Activity
{
// Your code here
}
2. Add the necessary imports for the Activity class:
import android.app.Activity; import android.os.Bundle;
3. Override the onCreate() method to set the content view for the activity:
@Override
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
4. Define any additional methods and properties that the activity requires.
5. Open the AndroidManifest.xml file and add the following code to declare the activity:
<activity android:name=".MainActivity" android:label="@string/app_name"> </activity>
NOTE: Save the manifest file and rebuild the app to apply the changes.
In summary, to declare an activity in Android with code implementation, you need to create a new Java class that extends the Activity class, override the onCreate() method to set the content view, define any additional methods and properties, and add the activity declaration to the AndroidManifest.xml file.
Declare intent filters in android with code implementation:
To declare intent filters in Android with code implementation, follow these steps:
1. Open the Java class that you want to add an intent filter to.
2. Create a new IntentFilter object and add the desired actions and categories:
IntentFilter filter = new IntentFilter(); filter.addAction(Intent.ACTION_SEND); filter.addCategory(Intent.CATEGORY_DEFAULT);
This code creates an intent filter that will match any intent with the ACTION_SEND action and the CATEGORY_DEFAULT category.
3. Optionally, add any additional data or MIME types that the intent filter should match:
filter.addDataScheme("http");
filter.addDataScheme("https");
filter.addDataType("text/plain");
This code adds two data schemes (http and https) and one data type (text/plain) to the intent filter.
4. Register the intent filter with the system by calling registerReceiver():
registerReceiver(receiver, filter);
This code registers a BroadcastReceiver object (named “receiver”) with the system, along with the intent filter that was defined.
5. Optionally, unregister the BroadcastReceiver and intent filter when they are no longer needed:
unregisterReceiver(receiver);
This code unregisters the BroadcastReceiver object and intent filter that were previously registered.
In summary, to declare intent filters in Android with code implementation, you need to create a new IntentFilter object and add the desired actions, categories, data, and MIME types, register the intent filter with the system using registerReceiver(), and optionally unregister the intent filter using unregisterReceiver() when it is no longer needed.
Declare permissions in android with code implementation:
To declare permissions in Android with code implementation, follow these steps:
1. Open the AndroidManifest.xml file in your Android Studio project.
2. Define the permission using the <permission> element. For example:</permission>
<permission android:name="com.example.myapp.PERMISSION" />
This code defines a permission named “com.example.myapp.PERMISSION”.
3. Define the protection level for the permission using the android:protectionLevel attribute. There are two possible values for this attribute: “normal” and “dangerous”. For example:
<permission android:name="com.example.myapp.PERMISSION" android:protectionLevel="dangerous" />
This code sets the protection level of the permission to “dangerous”.
4. Optionally, define a permission group using the android:permissionGroup attribute. For example:
<permission android:name="com.example.myapp.PERMISSION" android:protectionLevel="dangerous" android:permissionGroup="android.permission-group.CAMERA" />
This code places the permission in the “CAMERA” permission group.
5. Save the manifest file and rebuild the app to apply the changes.
6. To check whether the permission is granted at runtime, call the checkSelfPermission() method:
if (checkSelfPermission(Manifest.permission.CAMERA) == PackageManager.PERMISSION_GRANTED)
{
// Permission is granted
}
else
{
// Permission is not granted
}
This code checks whether the “CAMERA” permission is granted to the app. If it is granted, the first block of code is executed. If it is not granted, the second block of code is executed.
7. To request permission from the user at runtime, call the requestPermissions() method:
String[] permissions = {Manifest.permission.CAMERA};
int requestCode = 123;
requestPermissions(permissions, requestCode);
This code requests the “CAMERA” permission from the user, using a request code of 123. The user will see a dialog asking whether they want to grant the permission.
8. Handle the user’s response to the permission request by overriding the onRequestPermissionsResult() method:
@Override
public void onRequestPermissionsResult(int requestCode, String[] permissions, int[] grantResults)
{
if (requestCode == 123)
{
if (grantResults.length > 0 && grantResults[0] == PackageManager.PERMISSION_GRANTED)
{
// Permission is granted
}
else
{
// Permission is not granted
} } }
This code checks whether the user granted the “CAMERA” permission in response to the request. If the permission is granted, the first block of code is executed. If the permission is not granted, the second block of code is executed.
In summary, to declare permissions in Android with code implementation, you need to define the permission in the AndroidManifest.xml file, set the protection level and optional permission group, check whether the permission is granted at runtime using checkSelfPermission(), request the permission from the user using requestPermissions(), and handle the user’s response using onRequestPermissionsResult().
Managing the activity lifecycle in android
Managing the activity lifecycle in Android is important to ensure that your app behaves as expected and responds appropriately to changes in the device state. The activity lifecycle consists of several stages, each of which is important to manage correctly:
- onCreate(): This method is called when the activity is first created. It is here that you should initialize any resources that the activity will need.
- onStart(): This method is called when the activity becomes visible to the user. It is here that you should prepare the activity to be shown on screen.
- onResume(): This method is called when the activity is ready to interact with the user. It is here that you should start any animations or other interactions that require user input.
- onPause(): This method is called when the activity loses focus. It is here that you should stop any animations or other interactions that require user input.
- onStop(): This method is called when the activity is no longer visible to the user. It is here that you should release any resources that the activity no longer needs.
- onDestroy(): This method is called when the activity is about to be destroyed. It is here that you should clean up any resources that the activity has created.
Code implementation of activity lifecycle
To manage the activity lifecycle in Android, you should implement the appropriate methods to handle each stage of the lifecycle. For example:
public class MyActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
// Initialize resources needed by the activity
}
@Override
protected void onStart()
{
super.onStart();
// Prepare the activity to be shown on screen
}
@Override
protected void onResume()
{
super.onResume();
// Start any animations or other interactions that require user input
}
@Override
protected void onPause()
{
super.onPause();
// Stop any animations or other interactions that require user input
}
@Override
protected void onStop()
{
super.onStop();
// Release any resources that the activity no longer needs
}
@Override
protected void onDestroy()
{
super.onDestroy();
// Clean up any resources that the activity has created
} }
Code implementation to save and restore activity
In addition to these methods, you can also save and restore the state of your activity using the onSaveInstanceState() and onRestoreInstanceState() methods. These methods allow you to save and restore the state of any variables that your activity needs to remember between instances.
public class MyActivity extends AppCompatActivity
{
private int counter = 0;
@Override
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
if (savedInstanceState != null)
{
counter = savedInstanceState.getInt("counter");
}
// Initialize resources needed by the activity
}
@Override
protected void onSaveInstanceState(Bundle outState)
{
super.onSaveInstanceState(outState);
outState.putInt("counter", counter);
}
@Override
protected void onRestoreInstanceState(Bundle savedInstanceState)
{
super.onRestoreInstanceState(savedInstanceState);
counter = savedInstanceState.getInt("counter");
}
}
In summary, managing the activity lifecycle in Android is important to ensure that your app behaves as expected and responds appropriately to changes in the device state. You should implement the appropriate methods to handle each stage of the lifecycle, as well as save and restore the state of your activity using the onSaveInstanceState() and onRestoreInstanceState() methods.
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