In this post I will show you how to use the touch screen so that you can drag your finger across the screen, and it will switch the screen for you – “iPhone style”!

For this I will be implemented OnTouchListener and overrided the method OnTouch().

To start off, we need to create an Activity with two screens. The two screens will be implemented using a ViewFlipper in the main.xml layout file. Follow the steps in this blog post to set yourself up: Android: Switching screens in an Activity with animations (using ViewFlipper).

1. Now that you have yourself set up, open the Activity1 class.

2. Make the class implement OnTouchListener. The top of the class will look like this:

...
import android.view.View.OnTouchListener;

public class Activity1 extends Activity implements OnTouchListener{
...

2. You will have to override the OnTouch() method as well. If you were using eclipse, it might have created the method stub for you:

    @Override
    public boolean onTouch(View arg0, MotionEvent arg1) {
        // TODO Auto-generated method stub
        return false;
    }

Here is the method that you need to use instead:

    public boolean onTouch(View arg0, MotionEvent arg1) {

        // Get the action that was done on this touch event
        switch (arg1.getAction())
        {
            case MotionEvent.ACTION_DOWN:
            {
                // store the X value when the user's finger was pressed down
                downXValue = arg1.getX();
                break;
            }

            case MotionEvent.ACTION_UP:
            {
                // Get the X value when the user released his/her finger
                float currentX = arg1.getX();            

                // going backwards: pushing stuff to the right
                if (downXValue < currentX)
                {
                    // Get a reference to the ViewFlipper
                     ViewFlipper vf = (ViewFlipper) findViewById(R.id.details);
                     // Set the animation
                      vf.setAnimation(AnimationUtils.loadAnimation(this, R.anim.push_left_out));
                      // Flip!
                      vf.showPrevious();
                }

                // going forwards: pushing stuff to the left
                if (downXValue > currentX)
                {
                    // Get a reference to the ViewFlipper
                    ViewFlipper vf = (ViewFlipper) findViewById(R.id.details);
                     // Set the animation
                     vf.setInAnimation(AnimationUtils.loadAnimation(this, R.anim.push_left_in));
                      // Flip!
                     vf.showNext();
                }
                break;
            }
        }

        // if you return false, these actions will not be recorded
        return true;
    }

What I’ve done is added a CASE statement. On press down of the finger we save the current X value. On press up of the finger, after the dragging motion has finished, I check the X value again. I compare the two X values and I make a logical decision whether I should switch the screens forwards or backwards.

3. For the above to work, you need to add a global variable called downXValue that will store the X value when the finger was pressed down. Add the line below at the top of the class:

...
public class Activity1 extends Activity implements OnTouchListener{

    private float downXValue;

    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
...

4. Now, you we will edit the main.xml layout. This is different from the main.xml from the previous post in two ways:

• The two buttons that switched the views have been removed, because we don’t need them anymore and
• I added an ID to the main LinearLayout so that I may reference it in my code.

Here is the entire main.xml:

<?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:background="#ffffff"
    android:id="@+id/layout_main"
    >

    <ViewFlipper android:id="@+id/details"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent">  

        <LinearLayout
               android:orientation="vertical"
            android:layout_width="fill_parent"
            android:layout_height="fill_parent"
            android:background="#ffffff">

            <TextView android:id="@+id/tv_country"
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:textColor="#000000"
            android:textStyle="bold"
            android:textSize="18px"
            android:text="Country" >
            </TextView>
            <Spinner android:text=""
            android:id="@+id/spinner_country"
            android:layout_width="200px"
            android:layout_height="55px">
            </Spinner>
        </LinearLayout> 

        <LinearLayout
               android:orientation="vertical"
            android:layout_width="fill_parent"
            android:layout_height="fill_parent"
            android:background="#ffffff">

            <TextView android:id="@+id/tv_income"
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:textColor="#000000"
            android:textStyle="bold"
            android:textSize="18px"
            android:text="Income" >
            </TextView>
            <EditText android:text=""
            android:id="@+id/et_income"
            android:layout_width="200px"
            android:layout_height="55px">
            </EditText>
        </LinearLayout> 

    </ViewFlipper>

</LinearLayout>

5. We will have to add a listener for the OnTouch() event in the OnCreate() method of the Activity1 class will be. Add the following two lines:

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

        // Set main.XML as the layout for this Activity
        setContentView(R.layout.main);

        // Add these two lines
        LinearLayout layMain = (LinearLayout) findViewById(R.id.layout_main);
        layMain.setOnTouchListener((OnTouchListener) this);
...

6. You should also remove the two Button OnClick() events and listeners, because those buttons do not exist anymore. Here is the final version of the Activity1.java class:

package com.warriorpoint.taxman3;

import android.app.Activity;
import android.os.Bundle;
import android.view.MotionEvent;
import android.view.View;
import android.view.View.OnTouchListener;
import android.view.animation.AnimationUtils;
import android.widget.ArrayAdapter;
import android.widget.LinearLayout;
import android.widget.Spinner;
import android.widget.ViewFlipper;

public class Activity1 extends Activity implements OnTouchListener{

    float downXValue;

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

        // Set main.XML as the layout for this Activity
        setContentView(R.layout.main);

        // Add these two lines
        LinearLayout layMain = (LinearLayout) findViewById(R.id.layout_main);
        layMain.setOnTouchListener((OnTouchListener) this); 

        // Add a few countries to the spinner
        Spinner spinnerCountries = (Spinner) findViewById(R.id.spinner_country);
        ArrayAdapter countryArrayAdapter = new ArrayAdapter(this,
                    android.R.layout.simple_spinner_dropdown_item,
                    new String[] { "Canada", "USA" });
        spinnerCountries.setAdapter(countryArrayAdapter);

    }

    public boolean onTouch(View arg0, MotionEvent arg1) {

        // Get the action that was done on this touch event
        switch (arg1.getAction())
        {
            case MotionEvent.ACTION_DOWN:
            {
                // store the X value when the user's finger was pressed down
                downXValue = arg1.getX();
                break;
            }

            case MotionEvent.ACTION_UP:
            {
                // Get the X value when the user released his/her finger
                float currentX = arg1.getX();            

                // going backwards: pushing stuff to the right
                if (downXValue < currentX)
                {
                    // Get a reference to the ViewFlipper
                     ViewFlipper vf = (ViewFlipper) findViewById(R.id.details);
                     // Set the animation
                      vf.setAnimation(AnimationUtils.loadAnimation(this, R.anim.push_left_out));
                      // Flip!
                      vf.showPrevious();
                }

                // going forwards: pushing stuff to the left
                if (downXValue > currentX)
                {
                    // Get a reference to the ViewFlipper
                    ViewFlipper vf = (ViewFlipper) findViewById(R.id.details);
                     // Set the animation
                     vf.setInAnimation(AnimationUtils.loadAnimation(this, R.anim.push_left_in));
                      // Flip!
                     vf.showNext();
                }
                break;
            }
        }

        // if you return false, these actions will not be recorded
        return true;
    }

}

That’s it! Run it!

You will see that the button is gone and dragging across to the left or right will switch the screens!

Disclaimer: The back animation is not perfect, I still have to figure out why. It flickers a little. If you figure it out to animate properly please drop me a comment. Thanks!