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Android: first interactive app 

freyo
Joined:
07/27/2010
Posts:
128

April 01, 2011 15:46:16    Last update: April 01, 2011 15:47:57
Follow these steps to build your first app that allows you to enter input and click a button:
  1. Start from the Hello World example.
  2. Edit res/layout/main.xml, change the contents to: 
    <?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    >
<TextView  
    android:layout_width="fill_parent" 
    android:layout_height="wrap_content" 
    android:text="@string/question"
    />
<EditText
    android:layout_width="fill_parent" 
    android:layout_height="wrap_content" 
    android:id="@+id/name"
    />
<Button
     android:layout_height="wrap_content"
     android:layout_width="wrap_content"
     android:text="@string/sayhi"
     android:onClick="sayHi" />
<TextView  
    android:layout_width="fill_parent" 
    android:layout_height="wrap_content" 
    android:id="@+id/hello"
    />
</LinearLayout>

    This adds a text input field and a button to the screen. It also declaratively binds an event handler (onClick="sayHi") to the button.

  3. Add the string resources (res/values/strings.xml): 
    <?xml version="1.0" encoding="utf-8"?>
<resources>
    <string name="app_name">HelloWorld</string>
    <string name="greeting">Greeting</string>
    <string name="question">What\'s your name?</string>
    <string name="sayhi">Say Hi</string>
</resources>

  4. Implement the event handler (src/com/android/helloworld/HelloWorld.java): 
    package com.android.helloworld;

import android.app.Activity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.EditText;
import android.widget.TextView;

public class HelloWorld extends Activity
{
    private static final String LOG_TAG = "HelloWorld";

    private EditText nameField;
    private TextView greeting;

    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

	nameField = (EditText) findViewById(R.id.name);
	greeting = (TextView) findViewById(R.id.hello);
    }

    public void sayHi(View view) {
	CharSequence name = nameField.getText();
	greeting.setText("Hello " + name + "!");
    }
}

  5. Change the Activity label to Greeting (AndroidManifest.xml): 
    <?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
      package="com.android.helloworld"
      android:versionCode="1"
      android:versionName="1.0">
    <application android:label="@string/app_name" android:icon="@drawable/icon">
        <activity android:name="HelloWorld"
                  android:label="@string/greeting">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>
</manifest>

  6. Reinstall the debug package to the emulator: 
    ant install

  7. The screen should look like this:

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