Passare dati tra Activity

Obbiettivo:
       - Chiamare un'altra activity passando dati.
       - Leggere i dati che ci vengono passati da una activity.

Strumenti necessari:
     - Android Developer Tools (ADT) .
       - AVD / Smartphone debug.

Cose da fare:
      1) Creare il progetto
      2) Creo 2 layout
      3)  Creo 2 activity corrispondenti 
      4) Definire il Manifest



1) Creare il progetto
     - File >> New >> Android Application
      - Insert name project: TestAndroid
     - packcage: com.example.exercise.android
      - Finish

2) Creo 2 Layout
    - Definiamo i 2 layout, uno si chiamerà activity_one e l'altro activity_two.
      
      - res/layout/activity_one.xml

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"

    xmlns:tools="http://schemas.android.com/tools"

    android:layout_width="match_parent"

    android:layout_height="match_parent"

    android:paddingBottom="@dimen/activity_vertical_margin"

    android:paddingLeft="@dimen/activity_horizontal_margin"

    android:paddingRight="@dimen/activity_horizontal_margin"

    android:paddingTop="@dimen/activity_vertical_margin">

    <TextView

        android:id="@+id/tvHelloWorld"

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:text="hello world" />

    <Button

        android:id="@+id/btnPassData"

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:layout_below="@+id/tvHelloWorld"

        android:layout_marginTop="26dp"

        android:layout_centerHorizontal="true"
        android:onClick="clickStartTwoActivity"

        android:text="Pass Data to Another Activity" />

</RelativeLayout>

- res/layout/activity_two.xml

<?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"

    android:orientation="vertical" >

    <TextView

        android:id="@+id/respMessage"

        android:layout_width="match_parent"

        android:layout_height="wrap_content"

        android:gravity="center_horizontal"

        android:textAppearance="?android:attr/textAppearanceLarge" />

</LinearLayout>

3)  Creo 2 activity corrispondenti 

      - src/com/example/exercise/android/OneActivity.java
      - Avrà un metodo clickStartTwoActivity già stato definito nel layout (button) che eseguirà lo  start        di     un'altra activity passando come parametro  una stringa "Hello from mainActivity" :

 @Override

    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_one);

    }

        
        public void clickStartTwoActivit(View view){
      

       // 1. create l'intent relativa alla classe da chiamare.

        Intent intent = new Intent(getApplicationContext(),TwoActivity.class);

        // 2. put key/value data

        intent.putExtra("message", "Hello From MainActivity");

        // 3. or you can add data to a bundle

       

        Bundle extras = new Bundle();

        extras.putString("status", "Data Received!");

               

                //con il bundle si può anche passare un oggetto;

        // l'importante è avere un oggetto che implementa Serialize

        // e fare il put cosi:
        // extras.put("objKey", oggettoSerialize);

        // 4. add bundle to intent

        intent.putExtras(extras);

        // 5. start the activity

        startActivity(intent);

   }
 
      - src/com/example/exercise/android/TwoActivity.java
      - Nel metodo onCreate andremo a riprendere il valore (Hello From MainActivity) e lo setteremo nella textview presente nel secondo layout. Creiamo anche un Toast per visualizzare la scritta dello "status" che compare solo per qualche istante (essendo un toast)

 @Override

    protected void onCreate(Bundle savedInstanceState) {

        // TODO Auto-generated method stub

        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_two);

        // 1. get passed intent

        Intent intent = getIntent();

        // 2. get message value from intent

        String message = intent.getStringExtra("message");

        // 3. show message on textView

        ((TextView)findViewById(R.id.respMessage)).setText(message);

        // 4. get bundle from intent

        Bundle bundle = intent.getExtras();

        // 5. get status value from bundle

        String status = bundle.getString("status");

        // 6. show status on Toast

        Toast toast = Toast.makeText(this, status, Toast.LENGTH_LONG);

        toast.show();

    }

4) Definire il Manifest

- Tutte le activity devono essere dichiarate nel manifest.xml

 <?xml version="1.0" encoding="utf-8"?>

<manifest xmlns:android="http://schemas.android.com/apk/res/android"

    package="com.example.exercise.android"

    android:versionCode="1"

    android:versionName="1.0" >

    <uses-sdk

        android:minSdkVersion="8"

        android:targetSdkVersion="17" />

    <application

        android:allowBackup="true"

        android:icon="@drawable/ic_launcher"

        android:label="@string/app_name"

        android:theme="@style/AppTheme" >

        <activity

            android:name="com.example.exercise.android.OneActivity"

            android:label="@string/app_name" >

            <intent-filter>

                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />

            </intent-filter>

        </activity>

        <activity

            android:name="com.example.exercise.android.TwoActivity"

            android:label="@string/app_name" > 

        </activity>

    </application>

</manifest>