Get the co-ordinates of a touch event on Android

Question

I'm new to Android, I've followed the hello world tutorial through and have a basic idea of what's going on. I'm particularly interested in the touch screen of my T-Mobile Pulse so just to get me started I want to be able to write the co-ordinates of a tocuh event on the screen, so say the user touched the co-ordinate 5,2 - a textview on the screen would display that.

At present I have a simple program that just loads an xml file which contains the textview I intend to write the co-ordinates in.

Thank you in advance, I did Google for help and searched stackoverflow but everything I found either went way over my head or wasn't suitable for this. Cheers.

Answer 1

It sounds like you want to get touch events from the whole area of your layout for this particular test. Try attaching the touch listener to your parent view rather than a separate target view.

This isn't a very common approach. In most cases you will want to listen for touch events in a specific child view and if you have other views in your layout that handle touch events (such as a button) they'll take priority over a parent view. See http://developer.android.com/guide/topics/ui/ui-events.html for more info about handling UI events.

Layout (touch_viewer.xml):

<?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:id="@+id/parent" >
    <TextView android:id="@+id/text"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:text="Hello, World!" />
</LinearLayout>

And in your activity:

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.touch_viewer);

    final LinearLayout parent = (LinearLayout) findViewById(R.id.parent);
    final TextView text = (TextView) findViewById(R.id.text);
    parent.setOnTouchListener(new OnTouchListener() {
        public boolean onTouch(View v, MotionEvent ev) {
            text.setText("Touch at " + ev.getX() + ", " + ev.getY());
            return true;
        }
    });
}

Answer 2

You can use this function : http://developer.android.com/reference/android/view/View.html#setOnTouchListener(android.view.View.OnTouchListener)

You will probably put it in your onCreate method roughly this way (tested this time) :

Activity onCreate code

@Override
public void onCreate(Bundle savedInstanceState)
{
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);
    final TextView textView = (TextView)findViewById(R.id.textView);
    // this is the view on which you will listen for touch events
    final View touchView = findViewById(R.id.touchView);
    touchView.setOnTouchListener(new View.OnTouchListener() {
        @Override
        public boolean onTouch(View v, MotionEvent event) {
            textView.setText("Touch coordinates : " +
                String.valueOf(event.getX()) + "x" + String.valueOf(event.getY()));
                return true;
        }
    });
}

layout code

<?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:id="@+id/touchView" 
    android:background="#f00" 
    android:layout_weight="1" 
    android:layout_width="fill_parent" 
    android:layout_height="wrap_content" 
    />
<TextView  
    android:id="@+id/textView" 
    android:layout_width="fill_parent" 
    android:layout_height="wrap_content" 
    android:text="Hello World, TestActivity"
    />
</LinearLayout>

Edit: I tried my code and indeed there were a few errors. Anyway, with the layout I give you here it works on my emulator. Can you provide maybe more code/context so I can see what's wrong?

Answer 3

The corrected version without the errors:

import android.os.Bundle;
import android.app.Activity;
import android.view.Menu;
import android.view.MotionEvent;
import android.view.View;
import android.widget.TextView;
public class MainActivity extends Activity {
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        final TextView textView = (TextView) findViewById(R.id.textView);
        // this is the view on which you will listen for touch events
        final View touchView = findViewById(R.id.touchView);
        touchView.setOnTouchListener(new View.OnTouchListener() {
            @Override
            public boolean onTouch(View v, MotionEvent event) {
                textView.setText("Touch coordinates : "
                        + String.valueOf(event.getX()) + "x"
                        + String.valueOf(event.getY()));
                return true;
            }
        });
    }
    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }
}

Answer 4

The following works using a touch screen on the jetboy sample android app. Joes code worked with one tweak to make it shine the background thru. The only line I added was

android:background="#0000"
android:layout_height="fill_parent"   
android:layout_height="fill_parent" 

Thanks Joe (above).

@Override
public void onCreate(Bundle savedInstanceState)
{
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);
    final TextView textView = (TextView)findViewById(R.id.textView);
    // this is the view on which you will listen for touch events
    final View touchView = findViewById(R.id.touchView);
    touchView.setOnTouchListener(new View.OnTouchListener() {
        @Override
        public boolean onTouch(View v, MotionEvent event) {
            textView.setText("Touch coordinates : " +
                String.valueOf(event.getX()) + "x" + String.valueOf(event.getY()));
                return true;
        }
    });
}

layout code

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent">

    <com.android.samples.jetboy.JetBoyView android:id="@+id/JetBoyView"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent" />
        <TextView  
                android:id="@+id/touchView" 
                android:background="#0000" 
                android:layout_weight="1" 
                android:layout_width="fill_parent" 
                android:layout_height="fill_parent" 
        />
        <TextView  
                android:id="@+id/textView" 
                android:layout_width="fill_parent" 
                android:layout_height="fill_parent" 
                android:text="Hello World, TestActivity"
        />
</FrameLayout>