Simple Dialer Application

The projects to this point have emphasized that Android devices are highly-connected computers and data processors. But smartphones are also phones, so in this project we show how we can use an application to implement a phone call by loading the Android phone dialer with a number pre-inserted. Of course, you could do the same thing manually by opening the dialer screen and typing in the desired phone number, or invoking the number from a stored contacts list. So what is the advantage of having the computer do it?

The primary advantage of having the computer do it is that it can deal automatically with a dynamically-updated list of phone numbers, which need not be in the contacts list for the particular phone. Let's give two representative examples.

• Consider an application that displays a list of your friends, with contact data updated automatically from a social network. With the approach illustrated here, you can dial the number of a friend appearing in that list without knowing whether the number is in your contacts list, or whether it has been changed since you entered it into your contacts (assuming that the information supplied by the social networking site is current).


• As another example, consider a list of emergency phone numbers supplied to employees of a company. Those might change over time and it is problematic to assume that all employees will have the correct numbers stored in their phone contacts or otherwise easily accessible. But if each employee had a phone with an app developed along the lines of the present example, you only have to ensure that the server supplying the contact information is current to ensure that each employee has the resources to report an emergency immediately to the correct contact.

Both examples have the disadvantage that they require network data access. But even that issue can be dealt with by having the system cache its most recently acquired data, so that if the data network is down it is still likely that correct data will be used for the phone call. (Of course, if the voice wireless network is also down, you'll have to communicate by other means like landline phones or smoke signals.)

We will deal in separate projects with the issue of accessing data over the network and concentrate in this project on how to get an app to dial numbers, assuming that the numbers and associated data already are stored in arrays on the device.

Creating the Project in Android Studio

Following the general procedure in Creating a New Project, either choose Start a new Android Studio project from the Android Studio homepage, or from the Android Studio interface choose File > New > New Project. Fill out the fields in the resulting screens as follows,

where you should substitute your namespace for <YourNamespace> (com.lightcone in my case) and <ProjectPath> is the path to the directory where you will store this Android Studio Project (/home/guidry/StudioProjects/ in my case). If you have chosen to use version control for your projects, go ahead and commit this project to version control.

Inserting the Code

In the project that you have just created, open res/values/strings.xml and edit it to read

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

   <string name="app_name">SimpleDialer</string>
   <string name="action_settings">Settings</string>
   <string name="hello_world">Hello world!</string> 
   <string name="hello">SimpleDialer</string>
   <string name="main_label">My Friends</string>

</resources>

Then edit res/layout/activity_main.xml to read

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
   android:layout_width="fill_parent"
   android:layout_height="fill_parent"
   android:orientation="vertical"
   android:padding="15dip" >

   <TextView
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:layout_gravity="center"
      android:layout_marginBottom="25dip"
      android:text="@string/main_label"
      android:textColor="@color/colorPrimary"
      android:textSize="22sp" />

   <Button
      android:id="@+id/button1"
      android:layout_width="fill_parent"
      android:layout_height="wrap_content"
      android:textSize="18sp" />

   <Button
      android:id="@+id/button2"
      android:layout_width="fill_parent"
      android:layout_height="wrap_content"
      android:textSize="18sp" />

   <Button
      android:id="@+id/button3"
      android:layout_width="fill_parent"
      android:layout_height="wrap_content"
      android:textSize="18sp" />

   <Button
      android:id="@+id/button4"
      android:layout_width="fill_parent"
      android:layout_height="wrap_content"
      android:textSize="18sp" />

   <Button
      android:id="@+id/button5"
      android:layout_width="fill_parent"
      android:layout_height="wrap_content"
      android:textSize="18sp" />

   <Button
      android:id="@+id/button6"
      android:layout_width="fill_parent"
      android:layout_height="wrap_content"
      android:textSize="18sp" />

</LinearLayout>

Finally, open src/<YourNamespace>.simpledialer/MainActivity.java and edit it to read

package <YourNamespace>.simpledialer;
   
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.content.Intent;
import android.net.Uri;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;

public class MainActivity extends AppCompatActivity implements OnClickListener {

      private int entries = 6;
      private String phoneNum[];
      private String buttonLabels[];

      @Override
      protected void onCreate(Bundle savedInstanceState) {
               super.onCreate(savedInstanceState);
               setContentView(R.layout.activity_main);

               phoneNum = new String[entries];
               buttonLabels = new String[entries];

               // Populate the data arrays
               populateArrays();

               // Set up buttons and attach click listeners

               Button button1 = (Button)findViewById(R.id.button1);
               button1.setText(buttonLabels[0]);
               button1.setOnClickListener(this);

               Button button2 = (Button)findViewById(R.id.button2);
               button2.setText(buttonLabels[1]);
               button2.setOnClickListener(this);

               Button button3 = (Button)findViewById(R.id.button3);
               button3.setText(buttonLabels[2]);
               button3.setOnClickListener(this);

               Button button4 = (Button)findViewById(R.id.button4);
               button4.setText(buttonLabels[3]);
               button4.setOnClickListener(this);

               Button button5 = (Button)findViewById(R.id.button5);
               button5.setText(buttonLabels[4]);
               button5.setOnClickListener(this);

               Button button6 = (Button)findViewById(R.id.button6);
               button6.setText(buttonLabels[5]);
               button6.setOnClickListener(this);
      }

      // Launch the phone dialer

      public void launchDialer(String number){
               String numberToDial = "tel:"+number;
               startActivity(new Intent(Intent.ACTION_DIAL, Uri.parse(numberToDial)));
      }


      /** Method to populate the data arrays */

      public void populateArrays(){

               /** In a practical application the arrays phoneNum and buttonLabels could be 
                  * updated dynamically from the Web in this method.  For this project we just 
                  * hard-wire in some values to illustrate how to use such data, once obtained,
                  * to make phone calls. The names and numbers are made up.*/

               phoneNum[0] = "999-000-0001";
               phoneNum[1] = "999-000-0002";
               phoneNum[2] = "999-000-0003";
               phoneNum[3] = "999-000-0004";
               phoneNum[4] = "999-000-0005";
               phoneNum[5] = "999-000-0006";

               buttonLabels[0] = "Jane D. Arc";
               buttonLabels[1] = "John Doe";
               buttonLabels[2] = "Jane Doe";
               buttonLabels[3] = "Abraham Linking";
               buttonLabels[4] = "Mona Liza";
               buttonLabels[5] = "Issac Nuton";
      }

      /** Process button events */

      @Override
      public void onClick(View v) {
               switch (v.getId()) {

               case R.id.button1:
                        launchDialer(phoneNum[0]);
                        break;

               case R.id.button2:
                        launchDialer(phoneNum[1]);
                        break;

               case R.id.button3:
                        launchDialer(phoneNum[2]);
                        break;

               case R.id.button4:
                        launchDialer(phoneNum[3]);
                        break;

               case R.id.button5:
                        launchDialer(phoneNum[4]);
                        break;

               case R.id.button6:
                        launchDialer(phoneNum[5]);
                        break;
               }
      } 
}

Trying it Out

If you try this out on a device or emulator you should get the left screen below as the initial screen, and clicking on say the third button should give you something like (depending on the device) the screen below on the right.

At this point, (if the phone numbers were real and not made up) the user has only to hit the phone symbol at the bottom of the right screen to initiate the call, and also has options near the top to add the number to her list of contacts, create a new contact with it, or send an SMS message instead.

How it Works

Most of the above should be familiar: the layout in activity_main.xml, attaching click listeners to the buttons in MainActivity.java, and processing the corresponding events are all tasks that we have implemented in previous examples. Thus we reserve our comments for how the dialer works, and even these can be rather brief.

As noted above, the approach described here is most useful in dealing with a list of phone numbers updated dynamically over the network. We will discuss methods for accessing data over the network in other projects (one example is given in the Map Example project). Here we just have populateArrays() fill the arrays phoneNum[] and buttonLabels[] with some hardwired pseudo-data to illustrate how to make phone calls using the data contained in the arrays. The method launchDialer(String) initiates the phone call.

• Its key statement is startActivity(Intent intent), which is inherited by Activity from Context.


• For the argument of startActivity(Intent) we create an Intent using the constructor Intent (String action, Uri uri), which takes two arguments:


1. The string action specifies the action associated with the Intent. In this case it is set to the Intent class constant ACTION_DIAL, which indicates that the Intent is to dial a number as specified by the data (the second argument).


2. The second argument uri is a Uri (Uniform Resource Identifier) in the form of a string "tel:"+ telephone number that supplies the telephone number for the Intent action ACTION_DIAL..

That's it. Everything else is fairly standard Android that we have discussed in other projects.

Making the Button Display Orientation-Friendly

Before quitting, let's make one final improvement. If you flip the phone to horizontal display mode while the button menu is being displayed, depending on the size of your phone some of the six buttons may be off the screen. Following the discussion in the Animal Sounds project, let's specify alternative resources so that the menu of buttons displays better in horizontal mode:

1. In the left project panel, switch to Project view using the dropdown menu at the top of the panel. Right-click on app/src/main/res, select New > Directory, give the new folder the name layout-land, and click OK


2. Right-click on res/layout/activity_main.xml, copy it, and paste it into the new res/layout-land folder.


3. Edit the new res/layout-land/activity_main.xml file so that the buttons are now displayed in two rows of three each using the following XML.

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
   android:layout_width="fill_parent"
   android:layout_height="wrap_content"
   android:orientation="vertical"
   android:padding="15dip" >

   <TextView
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:layout_gravity="center"
      android:layout_marginBottom="25dip"
      android:text="@string/main_label"
      android:textColor="@color/colorPrimary"
      android:textSize="22sp" />

   <LinearLayout
      android:layout_width="fill_parent"
      android:layout_height="fill_parent"
      android:orientation="horizontal" >

      <Button
            android:id="@+id/button1"
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:textSize="18sp" />

      <Button
            android:id="@+id/button2"
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:textSize="18sp" />

      <Button
            android:id="@+id/button3"
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:textSize="18sp" />
   </LinearLayout>

   <LinearLayout
      android:layout_width="fill_parent"
      android:layout_height="fill_parent"
      android:orientation="horizontal" >

      <Button
            android:id="@+id/button4"
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:textSize="18sp" />

      <Button
            android:id="@+id/button5"
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:textSize="18sp" />

      <Button
            android:id="@+id/button6"
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:textSize="18sp" />
   </LinearLayout>

</LinearLayout>

Now if you flip the phone horizontal when the menu is showing, Android should switch automatically to the following display.

The reasons for switching to Project view in the above machinations has been described in Animal Sounds, and is reproduced in the following box.

When you click a button and go to the dialer though, whether it is displayed in portrait or landscape mode depends on the device and the app displaying the dialer (remember, we did not write that app, so we are at the mercy of its conventions). On a Moto-X that I used to have the dialer always displayed in portrait mode, but on an old Motorola Backflip that I used in the days when dinosaurs still roamed the Earth the dialer switched between portrait and landscape mode if the phone was rotated or the physical keyboard was opened or closed. On the Nexus 6P that I currently use, the dialer rotates between portrait and horizontal mode.

Last modified: July 8, 2016