Android ImageView图片透明区域不响应点击事件，不规则图片透明区域响应点击事件

<?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:gravity="center"
   android:id="@+id/mainLayout">
   
    <ImageView android:id="@+id/ImageView01"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:src="@drawable/transparent"/>
          
</LinearLayout>

package org.shuxiang.test;

import android.app.Activity;
import android.graphics.Bitmap;
import android.graphics.drawable.BitmapDrawable;
import android.os.Bundle;
import android.util.Log;
import android.view.MotionEvent;
import android.view.View;
import android.view.Window;
import android.view.View.OnClickListener;
import android.view.View.OnTouchListener;
import android.widget.ImageView;

public class MainActivity extends Activity
{
    private ImageView iv;
    private Bitmap bitmap;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        requestWindowFeature(Window.FEATURE_NO_TITLE);
        setContentView(R.layout.test);

        iv = (ImageView) findViewById(R.id.ImageView01);
        bitmap = ((BitmapDrawable) (iv.getDrawable())).getBitmap();
        
        iv.setOnClickListener(new OnClickListener(){
            @Override
            public void onClick(View v) {
                // TODO Auto-generated method stub    
                Log.i("Test", "点击");
            }
            
        });
        
        iv.setOnTouchListener(new OnTouchListener()
        {
            @Override
            public boolean onTouch(View arg0, MotionEvent arg1) 
            {
                // TODO Auto-generated method stub
                if(bitmap.getPixel((int)(arg1.getX()),((int)arg1.getY()))==0)
                {
                    Log.i("Test", "透明区域");
                    return true;//透明区域返回true
                }
                return false;
            }            
        });
    }
}