Handling touch and motion events
Introduction#
A summary of some of the basic touch/motion-handling systems in the Android API.
Parameters#
Listener | Details |
---|---|
onTouchListener | Handles single touches for buttons, surfaces and more |
onTouchEvent | A listener that can be found in surfaces(e.g. SurfaceView). Does not need to be set like other listeners(e,g. onTouchListener) |
onLongTouch | Similar to onTouch, but listens for long presses in buttons, surfaces and more. |
Buttons
Touch events related to a Button
can be checked as follows:
public class ExampleClass extends Activity implements View.OnClickListener, View.OnLongClickListener{
public Button onLong, onClick;
@Override
public void onCreate(Bundle sis){
super.onCreate(sis);
setContentView(R.layout.layout);
onLong = (Button) findViewById(R.id.onLong);
onClick = (Button) findViewById(R.id.onClick);
// The buttons are created. Now we need to tell the system that
// these buttons have a listener to check for touch events.
// "this" refers to this class, as it contains the appropriate event listeners.
onLong.setOnLongClickListener(this);
onClick.setOnClickListener(this);
[OR]
onClick.setOnClickListener(new View.OnClickListener(){
@Override
public void onClick(View v){
// Take action. This listener is only designed for one button.
// This means, no other input will come here.
// This makes a switch statement unnecessary here.
}
});
onLong.setOnLongClickListener(new View.OnLongClickListener(){
@Override
public boolean onLongClick(View v){
// See comment in onClick.setOnClickListener().
}
});
}
@Override
public void onClick(View v) {
// If you have several buttons to handle, use a switch to handle them.
switch(v.getId()){
case R.id.onClick:
// Take action.
break;
}
}
@Override
public boolean onLongClick(View v) {
// If you have several buttons to handle, use a switch to handle them.
switch(v.getId()){
case R.id.onLong:
// Take action.
break;
}
return false;
}
}
Surface
Touch event handler for surfaces (e.g. SurfaceView, GLSurfaceView, and others):
import android.app.Activity;
import android.os.Bundle;
import android.view.MotionEvent;
import android.view.SurfaceView;
import android.view.View;
public class ExampleClass extends Activity implements View.OnTouchListener{
@Override
public void onCreate(Bundle sis){
super.onCreate(sis);
CustomSurfaceView csv = new CustomSurfaceView(this);
csv.setOnTouchListener(this);
setContentView(csv);
}
@Override
public boolean onTouch(View v, MotionEvent event) {
// Add a switch (see buttons example) if you handle multiple views
// here you can see (using MotionEvent event) to see what touch event
// is being taken. Is the pointer touching or lifted? Is it moving?
return false;
}
}
Or alternatively (in the surface):
public class CustomSurfaceView extends SurfaceView {
@Override
public boolean onTouchEvent(MotionEvent ev) {
super.onTouchEvent(ev);
// Handle touch events here. When doing this, you do not need to call a listener.
// Please note that this listener only applies to the surface it is placed in
// (in this case, CustomSurfaceView), which means that anything else which is
// pressed outside the SurfaceView is handled by the parts of your app that
// have a listener in that area.
return true;
}
}
Handling multitouch in a surface
public class CustomSurfaceView extends SurfaceView {
@Override
public boolean onTouchEvent(MotionEvent e) {
super.onTouchEvent(e);
if(e.getPointerCount() > 2){
return false; // If we want to limit the amount of pointers, we return false
// which disallows the pointer. It will not be reacted on either, for
// any future touch events until it has been lifted and repressed.
}
// What can you do here? Check if the amount of pointers are [x] and take action,
// if a pointer leaves, a new enters, or the [x] pointers are moved.
// Some examples as to handling etc. touch/motion events.
switch (MotionEventCompat.getActionMasked(e)) {
case MotionEvent.ACTION_DOWN:
case MotionEvent.ACTION_POINTER_DOWN:
// One or more pointers touch the screen.
break;
case MotionEvent.ACTION_UP:
case MotionEvent.ACTION_POINTER_UP:
// One or more pointers stop touching the screen.
break;
case MotionEvent.ACTION_MOVE:
// One or more pointers move.
if(e.getPointerCount() == 2){
move();
}else if(e.getPointerCount() == 1){
paint();
}else{
zoom();
}
break;
}
return true; // Allow repeated action.
}
}