Tutorial

We will demonstrate Singletouch via an example with an own view. Create the Android project "de.vogella.android.touch.single" with the activity "SingleTouchView".

Create the following view class "SingleTouchEventView".

			
package de.vogella.android.touch.single;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Path;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;

public class SingleTouchEventView extends View {
	private Paint paint = new Paint();
	private Path path = new Path();

	public SingleTouchEventView(Context context, AttributeSet attrs) {
		super(context, attrs);

		paint.setAntiAlias(true);
		paint.setStrokeWidth(6f);
		paint.setColor(Color.WHITE);
		paint.setStyle(Paint.Style.STROKE);
		paint.setStrokeJoin(Paint.Join.ROUND);
	}

	@Override
	protected void onDraw(Canvas canvas) {
		canvas.drawPath(path, paint);
	}

	@Override
	public boolean onTouchEvent(MotionEvent event) {
		float eventX = event.getX();
		float eventY = event.getY();

		switch (event.getAction()) {
		case MotionEvent.ACTION_DOWN:
			path.moveTo(eventX, eventY);
			return true;
		case MotionEvent.ACTION_MOVE:
			path.lineTo(eventX, eventY);
			break;
		case MotionEvent.ACTION_UP:
			// nothing to do
			break;
		default:
			return false;
		}

		// Schedules a repaint.
		invalidate();
		return true;
	}
}

		

Add this view to your activity.

			
package de.vogella.android.touch.single;

import android.app.Activity;
import android.os.Bundle;

public class SingleTouchActivity extends Activity {
	
/** Called when the activity is first created. */
	@Override
	public void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(new SingleTouchEventView(this, null));
	}
}
		

If you run your application you will be able to draw on the screen with your finger (or with the mouse in the emulator).

The ScaleGestureDetector class allows to determine the predefined gesture of increasing, decreasing the size of the object.

Create the Android project "de.vogella.android.touch.scaledetector" and the Activity "ScaleDetectorTest" and create the following view class "ImageViewWithZoom".

			
package de.vogella.android.touch.scaledetector;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.drawable.Drawable;
import android.view.MotionEvent;
import android.view.ScaleGestureDetector;
import android.view.View;

public class ImageViewWithZoom extends View {
	private Drawable image;
	private float scaleFactor = 1.0f;
	private ScaleGestureDetector scaleGestureDetector;

	public ImageViewWithZoom(Context context) {
		super(context);
		image = context.getResources().getDrawable(R.drawable.icon);
		setFocusable(true);
		image.setBounds(0, 0, image.getIntrinsicWidth(),
				image.getIntrinsicHeight());
		scaleGestureDetector = new ScaleGestureDetector(context,
				new ScaleListener());
	}

	@Override
	protected void onDraw(Canvas canvas) {
		super.onDraw(canvas);
		// Set the image bounderies
		canvas.save();
		canvas.scale(scaleFactor, scaleFactor);
		image.draw(canvas);
		canvas.restore();
	}

	@Override
	public boolean onTouchEvent(MotionEvent event) {
		scaleGestureDetector.onTouchEvent(event);
		invalidate();
		return true;
	}

	private class ScaleListener extends
			ScaleGestureDetector.SimpleOnScaleGestureListener {
		@Override
		public boolean onScale(ScaleGestureDetector detector) {
			scaleFactor *= detector.getScaleFactor();

			// Don't let the object get too small or too large.
			scaleFactor = Math.max(0.1f, Math.min(scaleFactor, 5.0f));

			invalidate();
			return true;
		}
	}
}

		

Add this view to your activity.

			
package de.vogella.android.touch.scaledetector;

import android.app.Activity;
import android.os.Bundle;

public class ScaleDetectorTest extends Activity {
	
/** Called when the activity is first created. */
	@Override
	public void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(new ImageViewWithZoom(this));
	}
}
		

If you run your application zyou should be able to shrink / enlarge the image via a multi-touch gesture (pitch zoom).

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