CODEWITHSUNDEEP
android
NumenorForLife
NumenorForLife

Reputation: 1746

Android Starting an Activity Introduction - Defining text_message

I am working on the Android guide here: http://developer.android.com/training/basics/activity-lifecycle/starting.html and there is reference to a variable that has never been created 

mTextView = (TextView) findViewById(R.id.text_message);

Where am I supposed to define text_message?

Thanks for your help!

Update: I believe the chunk of code from which this is taken is merely an example, and not to be incorporated with the application we created in the previous part of the tutorial.

Upvotes: 0

Views: 1217

Answers (2)

codeMagic
codeMagic

Reputation: 44571

It is declared here 

TextView mTextView; // Member variable for text view in the layout  // Right here

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

Declaring it outside of a method, generally right after class declaration, makes it a member variable so it can be used anywhere in the class, including inner classes and listeners. You just can't initialize it in the same place because you haven't inflated your Layout yet by calling setContentView()

Short example

public class MyActivity extends Activity
{
    TextView mTextView; // Member variable for text view in the layout

    @Override
    public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    // Set the user interface layout for this Activity
    // The layout file is defined in the project res/layout/main_activity.xml file
    setContentView(R.layout.main_activity);

    // Initialize member TextView so we can manipulate it later
    mTextView = (TextView) findViewById(R.id.text_message);   // findViewById) looks for the id you set in the xml file, here text_message
}

R.id.text_message is defined in the main_activity.xml which could look something like this

    <?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">
    <TextView
        android:id="@+id/text_message"   <!-- this is where the R.id.text_message comes from -->
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textSize="20dp"/>
    </LinearLayout>

That documentation is definitely good to go through but you may want to start Here and go through a short example starting from creating a project

Upvotes: 1

Sunil Kumar
Sunil Kumar

Reputation: 7082

use this way define the xml layout inside the folder of res/layout/main.xml and set in setconentView.

private TextView mTextView = null; 
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    stContentView(R.layout.main);
mTextView = (TextView) findViewById(R.id.text_message);
mTextView.setText("Hello");
}

Upvotes: 0

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