Apr 12, 2012

Detect Touch Event part IV - get touch area

Previous article: Detect Touch Event part III - get touch pressure and size

The method getTouchMajor() and getTouchMinor() (getTouchMajor(int pointerIndex) and getTouchMinor(int pointerIndex) for multi-touch) of MotionEvent returns the length of the major and minor axis of an ellipse that describes the touch area.

Example:

get touch area

package com.TestSingleTouch;

import android.app.Activity;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.RectF;
import android.os.Bundle;
import android.view.MotionEvent;
import android.view.View;
import android.widget.LinearLayout;
import android.widget.TextView;

public class TestSingleTouch extends Activity {

public class TouchView extends View {

private Paint paint = new Paint(Paint.ANTI_ALIAS_FLAG);
private float x, y;
private float touchMajor, touchMinor;
boolean touching = false;

float pressure = 0; //Touch pressure
float size = 0; //Touch size
final static float PRESET_PRESSURE = 0xFF;
final static float PRESET_SIZE = 300;

public TouchView(Context context) {
super(context);
// TODO Auto-generated constructor stub
}

@Override
protected void onDraw(Canvas canvas) {
// TODO Auto-generated method stub
if(touching){

paint.setStyle(Paint.Style.FILL_AND_STROKE);
paint.setStrokeWidth(1);

paint.setColor(Color.WHITE);
RectF ovalTouch = new RectF(x-touchMajor/2, y-touchMinor/2, x+touchMajor/2, y+touchMinor/2);

canvas.drawOval(ovalTouch, paint);
}
}

@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
// TODO Auto-generated method stub
setMeasuredDimension(MeasureSpec.getSize(widthMeasureSpec),
MeasureSpec.getSize(heightMeasureSpec));
}

@Override
public boolean onTouchEvent(MotionEvent event) {
// TODO Auto-generated method stub

pressure = event.getPressure();
if(pressure > 1){
pressure = 1;
}

size =event.getSize();

String act;

int action = event.getAction();

switch(action){
case MotionEvent.ACTION_MOVE:
act = "ACTION_MOVE\n";
x = event.getX();
y = event.getY();
touchMajor = event.getTouchMajor();
touchMinor = event.getTouchMinor();
touching = true;
break;
case MotionEvent.ACTION_DOWN:
act = "ACTION_DOWN\n";
x = event.getX();
y = event.getY();
touchMajor = event.getTouchMajor();
touchMinor = event.getTouchMinor();
touching = true;
break;
case MotionEvent.ACTION_UP:
act = "ACTION_UP\n";
touching = false;
break;
default:
act = "XXX\n";
touching = false;
}

act += event.toString();
textView.setText(act);

invalidate();
return true;
}
}

TextView textView;

/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
//setContentView(new TouchView(this));
textView = new TextView(this);
textView.setText("Waiting");
TouchView touchView = new TouchView(this);
LinearLayout mainScreen = new LinearLayout(this);
mainScreen.setOrientation(LinearLayout.VERTICAL);
mainScreen.addView(textView);
mainScreen.addView(touchView);
setContentView(mainScreen);
}
}


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