MonoAndroid: Calling secondary activity

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Introduction

In this article I will try to explain activating\starting second activity from MainActivity, which would be our Step1 and in second step we will discuss returning data from second activity to main activity. I would be using MonoAndroid to build this application and for previous articles in series, please refer bottom part of article.

In this article, I will create Indian film star biography application, where main activity will contain ListView which will display small image and name of the film star and on clicking on the item will new activity which will display information like age and brief biography of selected film star.

Step by step we move forward

1. Create Android application by selecting New ->Solutions and provide its name “CallingSecondActivity” 
2. Now do following changes in the the Main.axml file under Layout, after adding  UI code, it looks something like this:
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   <?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">  
       <ListView
           android:minWidth="25px"
           android:minHeight="25px"
           android:layout_width="fill_parent"
           android:layout_height="wrap_content"
           android:id="@+id/lstFlimStars" />
   </LinearLayout>

   In this layout, i have added ListView, which i would fill with name and small image of filmstar's.

3. Now add class by name FlimStarInformationModal and inherit from abstract generic class Java.Lang.Object, here is code for FlimStarInformationModal class.. Once added the code  look like this:
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   [Serializable]
   public class FlimStarInformationModal :Java.Lang.Object
   {
       public string FilmStarName {get;set;}
       public int FlimStarImageID {get;set;}
       public int FlimStarIconImageID {get;set;}
       public string FilmStarBio {get;set;}
       public string FilmStarAge { get; set;}
   }

   Each object of this model class will be used by listview and secondary activity to display data.

4. Since we don’t have database or web-service to get data, I have created a method in MainActivity, where we have hard-coded data for displaying it in different UI control.
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   void CreateProjectDS ()
   {
       _lstFlimStarInfo = new List<flimstarinformationmodal> ();
       _lstFlimStarInfo.Add (new FlimStarInformationModal () {
           FilmStarName = "Amitabh Bachan",
           FilmStarAge = "71 Year Old",
           FlimStarImageID = Resource.Drawable.ABSR,
           FlimStarIconImageID = Resource.Drawable.ABSRIco,
           FilmStarBio = "Amitabh Harivansh Bachchan (born 11 October 1942) is an Indian film actor. 
             He first gained popularity in the early 1970s as the \"angry young man\" 
             of Hindi cinema, and has since appeared in over 180 Indian films in a career spanning 
             more than four decades. Bachchan is widely regarded as one of the greatest and most 
             influential actors in the history of Indian cinema.So total was his dominance of the 
             movie scene in the 1970s and 1980s that the French director Francois Truffaut called 
             him a \"one-man industry\"." +
            "shares with Kamal Hassan and Mammootty), a number of awards at international 
            film festivals and award ceremonies and fourteen Filmfare Awards. 
            He is the most-nominated performer in any major acting category at Filmfare, 
            with 39 nominations overall. In addition to acting, Bachchan has worked as a 
            playback singer, film producer and television presenter. He also had a stint 
            in politics in the 1980s. The Government of India honoured him with the Padma 
            Shri in 1984 and the Padma Bhushan in 2001 for his contributions towards the arts.",
       });
   
       _lstFlimStarInfo.Add (new FlimStarInformationModal () {
           FilmStarName = "Shahrukh Khan",
           FlimStarImageID = Resource.Drawable.SRK,
           FlimStarIconImageID = Resource.Drawable.SRKIco,
           FilmStarAge = "48 Year Old",
           FilmStarBio = "Shahrukh Khan (born 2 November 1965), often credited 
             as Shah Rukh Khan and informally referred as SRK, is an Indian film actor. 
             Referred to in the media as \"Badshah of Bollywood\", \"King Khan\" 
             and \"King of Romance\", Khan has acted in 75 Hindi films in genres ranging 
             from romantic dramas to action thrillers.[4][5][6][7] His contributions to the film 
             industry have garnered him numerous achievements, including fourteen Filmfare Awards 
             from thirty nominations. His eighth Filmfare Best Actor Award win made him the most 
             awarded Bollywood actor of all time in that category, tied only with actor Dilip Kumar. 
             In 2005, the Government of India honoured him with the Padma Shri for his contributions 
             towards Indian cinema." +
           "Khan is considered to be one of the biggest film stars in cinematic history, 
             with a fan following claimed to number in the billions; in 2011, the Los Angeles 
             Times called him \"the world's biggest movie star.\"[19] He has also 
             been regularly featured in the listing of the most powerful names in Indian Cinema 
             and in 2008, Newsweek named him one of the 50 most powerful people in the world.[5] 
             Khan has an estimated net worth of over US $600 million(INR25 billion).",
       });
   
       _lstFlimStarInfo.Add ( new FlimStarInformationModal () {
           FilmStarName = "Hrithik Roshan",
           FlimStarImageID = Resource.Drawable.HR,
           FlimStarIconImageID = Resource.Drawable.HRIco,
           FilmStarAge = "39 Year Old",
           FilmStarBio = "Hrithik Roshan (born on 10 January 1974) is an Indian film actor 
             and professional dancer.[1][2] Having appeared as a child actor in several 
             films throughout the 1980s, Roshan made his film debut in a leading role in 
             Kaho Naa... Pyaar Hai in 2000. His performance in the film earned him Filmfare 
             Awards for Best Actor and Best Male Debut. He followed it with leading roles in Fiza 
             and Mission Kashmir (both released in 2000) and a supporting part in the blockbuster 
             Kabhi Khushi Kabhie Gham (2001)" +
           "Following through with several unnoticed performances from 2002 to 2003, he starred 
             in the blockbusters Koi... Mil Gaya (2003) and its sequel Krrish (2006), 
             both of which won him numerous Best Actor awards.[3] Roshan received his 
             third Filmfare Award for Best Actor in 2006 for his performance in the action 
             film Dhoom 2, and his fourth for Jodhaa Akbar[4] for which he was also awarded 
             at the Golden Minbar International Film Festival. He later received further 
             acclaim for his work in Guzaarish (2010), Zindagi Na Milegi Dobara (2011) 
             and Agneepath (2012), his biggest commercial success so far. These accomplishments 
             have established him as a leading contemporary actor of Hindi cinema.",
       });
   }

5. Now, since we are using custom model class, we have to write custom adapter for ListView to display data inside it. You can read more about creating custom BaseAdapater here.

   Now code for our custom base adapter by name FlimStarAdapater looks like this:

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   internal class FlimStarAdapater:BaseAdapter<FlimStarInformationModal>
   {
       Activity _mainActivity;
       List<FlimStarInformationModal> _lstFlimStarInfo;
   
       public FlimStarAdapater (Activity mainActivity,
                 List<FlimStarInformationModal> lstFlimStarInfo)
       {
           _mainActivity = mainActivity;
           _lstFlimStarInfo = lstFlimStarInfo;            
       }
   
       #region implemented abstract members of BaseAdapter
       public override long GetItemId (int position)
       {
           return position;
       }
       public override View GetView (int position, View convertView, ViewGroup parent)
       {
           var currentObj = this [position];
           if (convertView == null)
               convertView =_mainActivity.LayoutInflater.Inflate (
                    Android.Resource.Layout.ActivityListItem,null);
   
           convertView.FindViewById<TextView> (Android.Resource.Id.Text1).Text = currentObj.FilmStarName;
           convertView.FindViewById<ImageView> 
             (Android.Resource.Id.Icon).SetImageResource(currentObj.FlimStarIconImageID);
   
           return convertView;
       }
       public override int Count {
           get {
               return _lstFlimStarInfo != null ? _lstFlimStarInfo.Count : -1;
           }
       }
       #endregion
       #region implemented abstract members of BaseAdapter
       public override FlimStarInformationModal this [int index] {
           get {
               return _lstFlimStarInfo != null ? _lstFlimStarInfo[index] : null;
   
           }
       }
       #endregion
   }

   Now our baseadapter is ready, data source is also ready, we can use following code to attach custom adapter to ListView in MainActivity.cs file.

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   var lstvwObject = this.FindViewById<ListView> (Resource.Id.lstFlimStars);
   
   if (lstvwObject != null) {
       lstvwObject.Adapter = new FlimStarAdapater (this, _lstFlimStarInfo);
       lstvwObject.ItemClick += OnFilmStarListViewClickSA;
   }

   The OnFilmStarListViewClickSA method will called when we click on item present in listview. Here we have written code for passing information second activity and starting it. FullInformationActivity is name of second activity class which will handle data sent by main activity.

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   void OnFilmStarListViewClickSA  (object sender, AdapterView.ItemClickEventArgs e)
   {
       Intent myIntent = new Intent (this, typeof(FullInformationActivity));
       var cItem = _lstFlimStarInfo[e.Position];
       myIntent.PutExtra ("FilmStarName", cItem.FilmStarName);
       myIntent.PutExtra("FlimStarImageID", cItem.FlimStarImageID);
       myIntent.PutExtra("FilmStarBio", cItem.FilmStarBio);
       myIntent.PutExtra("FilmStarAge", cItem.FilmStarAge);
       StartActivity(myIntent);
   }

6. Now, add layout by name FullInformationLayout.xaml, which will act as UI frontend for FullInformationActivity.cs, add following code to it:
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<?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"
    android:minWidth="25px"
    android:minHeight="25px">
    <RelativeLayout
        android:minWidth="25px"
        android:minHeight="25px"
        android:layout_width="fill_parent"
        android:layout_height="match_parent"
        android:id="@+id/relativeLayout1">
        <TextView
            android:text="Name"
            android:textAppearance="?android:attr/textAppearanceMedium"
            android:layout_width="121.5dp"
            android:layout_height="wrap_content"
            android:id="@+id/lblName"
            android:layout_marginLeft="14.2dp"
            android:layout_marginTop="10.0dp"
            android:textColor="#FF00FF" />
        <TextView
            android:text="Age"
            android:textAppearance="?android:attr/textAppearanceMedium"
            android:layout_width="121.5dp"
            android:layout_height="wrap_content"
            android:id="@+id/lblAge"
            android:layout_marginLeft="14.2dp"
            android:layout_marginTop="10.0dp"
            android:layout_below="@+id/lblName" />
        <ImageView
            android:src="@android:drawable/ic_menu_gallery"
            android:layout_width="96dp"
            android:layout_height="120dp"
            android:id="@+id/imageView1"
            android:layout_toRightOf="@+id/lblName"
            android:layout_marginLeft="35.0dp"
            android:layout_marginBottom="4.0dp" />
        <ScrollView
            android:minWidth="25px"
            android:minHeight="25px"
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:id="@+id/scrollView1"
            android:layout_marginLeft="14.2dp"
            android:layout_below="@+id/imageView1"
            android:layout_above="@+id/btnGoBack">
            <TextView
                android:text="Biography"
                android:textAppearance="?android:attr/textAppearanceSmall"
                android:layout_width="match_parent"
                android:layout_height="match_parent"
                android:id="@+id/lblBiography"
                android:layout_marginRight="4dp"
                android:layout_weight="1"
                android:textColor="#FF0000" />
        </ScrollView>
        <Button
            android:text="Go Back!"
            android:layout_width="fill_parent"
            android:layout_height="50dp"
            android:id="@+id/btnGoBack"
            android:layout_alignParentBottom="true"
            android:layout_marginTop="8.0dp" />
    </RelativeLayout>
</LinearLayout>

UI Creation step is as follow:

• Add RelativeLayout
• Add TextView by id "@+id/lblName" inside RelativeLayout
• Add another TextView by id "@+id/lblAge" and set RelativeLayout dependency property android:layout_below "@+id/lblName", placing below name textview
• Add ImageView by id "@+id/ imageView1" and set RelativeLayout dependency property android: layout_toRightOf="@+id/lblName", placing right side of name textview 
• Place button by id "@+id/btnGoBack" and set android:layout_alignParentBottom = "true", so that it gets placed at the bottom of the layout. 
• Add ScrollView as chances of biography extending the screen are greater. Here I have set two RelativeLayout dependency android:layout_below="@+id/imageView1" and android:layout_above="@+id/btnGoBack", for placing ScrollView between ImageView and Button
• Last, but not the least, add TextView by id "@+id/lblBiography", which will display the filmstar biography
• I have set UI control layout margin, to make UI looks good.

Once created, UI looks like this

Called Activity UI

7. Now add activity class by name FullInformationActivity, which will backend for FullInformationLayout. Here I have added method for updating sent data from MainActivity:
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void UpdateActivityWithInformation ()
{
    var txtFilmStarInfo = FindViewById<TextView> (Resource.Id.lblName);
    var txtage = FindViewById<TextView> (Resource.Id.lblAge);
    var txtFilmStarBio = FindViewById<TextView> (Resource.Id.lblBiography);
    var ivFilmStar = FindViewById<ImageView> (Resource.Id.imageView1);

    txtFilmStarInfo.Text = this.Intent.GetStringExtra("FilmStarName");
    ivFilmStar.SetImageResource(this.Intent.GetIntExtra("FlimStarImageID",-1));
    txtFilmStarBio.Text = this.Intent.GetStringExtra("FilmStarBio");
    txtage.Text = this.Intent.GetStringExtra("FilmStarAge");
}

Following is code for btnGoBack, where I will call Finish() to close the activity.

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protected override void OnCreate (Bundle bundle)
{
    base.OnCreate (bundle);
    SetContentView (Resource.Layout.FullInformationLayout);
    Button btnGoBack = FindViewById<Button> (Resource.Id.btnGoBack);

    if(btnGoBack!=null)
        btnGoBack.Click += (object sender, EventArgs e) => 
    {
        SetResult(Result.Ok);
        Finish();
    };
}




8. Now Build and Run the application:

   Initial Screen	On Clicking ListView item	On Clicking Go Back Button

9. Here is small flowchart diagram to explain what we have done above:

Flowchart I




10. Now, let’s work on step 2 now, returning data from the called activity. For that we need to StartActivityForResult API passing intent data as it is as we used StartActivity API previously and one unique request code to indentify request coming back:
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    ///--- In MainActivityClass
    const int MY_RESULT_CODE = 101;
    ///-- In OnFilmStarListViewClickSA Method
    StartActivityForResult(myIntent,MY_RESULT_CODE);

    
    
11. Now modify btnGoBack click code, to return data from called activity, you have to create Intent, put data inside it and using SetResult, push data back to main activity.
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Button btnGoBack = FindViewById<Button> (Resource.Id.btnGoBack);

if(btnGoBack!=null)
    btnGoBack.Click += (object sender, EventArgs e) => 
{
    Intent myIntent = new Intent();
    myIntent.PutExtra("returnData", this.Intent.GetStringExtra("FilmStarName"));
    SetResult(Result.Ok,myIntent);
    Finish();
};

12. You have used StartActivityForResult to start activity and also have returned the data from called activity. For that you have to override OnActivityResult for handling returned data. It has three parameters requestCode, resultCode, and IntentData. requestCode contains requestCode sent at the time of Starting Activity, resultCode and intentData contain value set in SetResult API from called Activity.
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protected override void OnActivityResult(int requestCode, Result resultCode, Intent data){
    if (requestCode == MY_RESULT_CODE) {
        switch (resultCode) {
        case Result.Ok:
            Toast.MakeText (this, data.GetStringExtra ("returnData"), ToastLength.Long).Show ();
            break;
        default:
            break;
        }

    }
}

13. Build and Run again

Initial Screen	On Clicking ListView item	On Clicking Go Back Button

You can see Toast visible in third image, showing data returned by called activity.

14. Here is small flowchart diagram to explain what we have done above:

Flowchart II

Points of Interest

I have used MonoAndroid for C# and Xamarin Studio to build this tutorial.  Watch out, if I continue learning it, you can expect more articles coming soon. 

Though Xamarin Studio is proprietary software, however they provide free starter version to built, test and publish android application. I am using same for my learning. 

Articles in this series!

• MonoAndroid: Writing custom generic BaseAdapter in C#
• MonoAndroid: Using GridView in your mobile application
• MonoAndroid: Using TabHost in your mobile applications
• MonoAndroid: Using Fragments in mobile app 
• MonoAndroid: Using .NET webservice (ASMX)
• MonoAndroid: Using Started Service 
• MonoAndroid: Writing ExpandableListView amd BaseExpandableListAdapter in C#
• MonoAndroid: Using AlertDialog

Tips/Tricks in this Series

• MonoAndroid: Android Notification service
• MonoAndroid: Using bound Services

History

• 10-Oct-2013: First version. 
• 05-Nov-2013: Updated article in series 
• 22-Nov-2013: Updated other article section