Create New Android Activity

Create New Activity
ANDROID MOBILE APPLICATION
TRAINING VIDEO - 3
Copyright © 2020 Transpose Solutions. All Rights Reserved.

OVERVIEW
In this tutorial, we will learn how to create
new activity to an exisiting android project,
send user input from one activity to another
and add navigation button to the app bar for
the user to return to parent screen.

OPEN AN EXISTING PROJECT
From your task bar/start menu, click open “Android
Studio”
In the Welcome to Android Studio window:
 Click Open an existing Android Studio project.
In the Open File or Project window:
 Go to Android Studio Projects Folder and Select My Mobile App – the project
we created in our earlier tutorial and click OK.
Note: If you have not viewed our earlier tutorial – create new layout, please
view that before starting this tutorial.

OPEN MAIN ACTIVITY CLASS
Android Studio main window appears after some process. We
need to open MainActivity class (Jave file) – code behind the
main_activity.xml:
Click Open app > java > com.transposesolutions.mymobileapp >
MainActivity.
Add a Method “displayMessage”
Note: This training material uses Android Studio v3.6.1. Package name
“com.transposesolutions.mymobileapp” is our domain and app name, you
should have your own package name.

ADDING A METHOD
We need to create the displayMessage() in the MainActivity class, this method will be used to
start a new activity when app user clicks the submit button.
Click open – app > java > com.transposesolutions.mymobileapp > MainActivity
Add the following displayMessage() method stub inside AppCompactActivity:
Note: You might see an error because Android Studio cannot resolve the View class used as the method argument. To clear the error, click the View declaration,
place your cursor on it, and then press Alt+Enter, or Option+Enter on a Mac, to perform a Quick Fix. If a menu appears, select Import class.

DEFINE - CLICK EVENT HANDLER
Now, let us define the click event handler for the “Submit” button in the file
activity_main.xml by adding the android:onClick:
Open app > res > layout > activity_main.xml.
Select the button in the Layout Editor.
In the Attributes window, locate the onClick property
Select “displayMessage” from its drop-down list.
Now when the “Submit” button is tapped, the system calls the displayMessage() method.
Note: We need to add few lines of code to the displayMessage(), so that the system
can read the contents of the EditText (User input) and deliver that text to another
activity which we will create next by adding a new activity to display the user input
from main_activity_xml.

ADD NEW ACTIVITY
Let us add new activity to the project to display the user input from
main_activity.xml.
Please follow the following steps to add a new activity:
In the Project window, right-click the app folder and select New > Activity >
Empty Activity.
In the Configure Activity window, enter "DisplayActivity" for Activity Name.
Leave all other properties set to their defaults and click Finish.
Now, main window appears after some processes with activity_display.xml opened
with the layout editor.

OPEN – LAYOUT EDITOR
Let us open the layout editor, set the margin to the display_activity.xml:
If your editor shows the XML source, click the Design tab.
Click Select Design Surface and select Blueprint.
Click Show in the Layout Editor toolbar and make sure that Show All
Constraints is checked.
Make sure Autoconnect is off.
Click Default Margins in the toolbar and select your margin to “24”. If needed,
you can adjust the margins for each view later.
Click Device for Preview in the toolbar and select 5.5, 1440 × 2560, 560 dpi
(Pixel XL).

ADD WIDGETS
Let us add new UI string to app “app_message”, add the following widgets to the
display_activity.xml and apply styles:
TextView with ID: “welcome_message” – To display a welcome message and set the
following:
Set layout width: 0dp; layout margin top: 20dp
Set widget property to “Center - Horizontally”
Locate the text property, which is currently set to “Name” and delete the value. Then, click
“Pick a Resource” and select “app_message” from the list.
Set text gravity to “Center”; Set text size: 30 sp and text color: @color/colorAccent
TextView with ID: “user_input” – To display the text entered by the app user in the main
activity
Set layout width: 0dp; layout margin top: 20dp
Set widget property to “Center - Horizontally” and layout_constraint top to bottom
Set text gravity to “Center”; Set text size: 30 sp and text color: @color/colorPrimary

ADD NAVIGATION
Let us add a navigation button to app bar for the app user to return to
main_activity.xml, to do that we need to declare “main_activity.xml is the parent screen in
the AndroidManifest.xml:
 Open the file at app > manifests > AndroidManifest.xml
 locate the <activity> tag for DisplayMessageActivity replace <activity> tag with
below code:
Next, we need to go back to MainActivity class file to add few lines of code to the displayMessage(), so that the
system can read the contents of the field and deliver that text to display_activity.xml.

USING - INTENT OBJECT
Let us open MainActivity Class and add few lines of code to the displayMessage(), for this purpose,
we use “Intent” object to start display_activity.xml and “putExtra()” method to add the user
entered values from the “EditText” to Intent.
Fill in the following code to displaymessage(), add SEND_MESSAGE constant and import required
class:
Note: For more technical documents about “Intent” can be accessed from Google developer guide: https://developer.android.com/reference/android/content/Intent

DISPLAYMESSAGE()
Let us examine, what does the code we just added to the displayMessage():
The Intent constructor takes two parameters, a Context and a Class.
The Context parameter is used first because the Activity class is a subclass of Context.
The Class parameter of the app component, to which the system delivers the Intent,
is, in this case, the activity to start.
The putExtra() method adds the value of EditText to the intent. An Intent can carry
data types as key-value pairs called extras.
Your key is a public constant SEND_MESSAGE because the next activity uses the key
to retrieve the text value.
The startActivity() method starts an instance of the DisplayActivity that's specified
by the Intent.

DISPLAY USER INPUT
To display the user input from main_activity.xml to display_activity.xml. For this purpose, we use
Intent object and “getIntent()” method.
Let us open DisplayActivity Class and fill in the following code to onCreate() Method and import
required class :
Now, we can run the app to view the changes we have done so far in this tutorial.

RUN YOUR APP
Use Android studio emulator to run your app:
In the toolbar, select your app from the run/debug configurations drop-down
menu.
 From the target device drop-down menu, select the AVD that you want to run
your app on.
 Click Run
Android Studio installs the app on the AVD and starts the
emulator.

Conclusion
We hope you were able to follow the instruction mentioned this tutorial, please find the
final output of screen we developed so far:
Main_Activity.xml Display_Activity.xml

Thank you for watching the video!
We hope the training video 1, 2 and 3
was helpful. Please read the
description of this video and external
weblink provided to learn more…

Create New Android Activity

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