android自定义View及事件

直接如题，本例效果如下图，继承自ImageView，后面画了个圆，圆的大小在布局文件设置，点击圆内会有事件相应，圆外无响应。

先看自定义的MyView代码

package test.bg;

import android.content.Context;
import android.content.res.TypedArray;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.graphics.RectF;
import android.util.AttributeSet;
import android.util.Log;
import android.view.MotionEvent;
import android.view.ViewGroup.LayoutParams;
import android.view.ViewTreeObserver;
import android.view.ViewTreeObserver.OnGlobalLayoutListener;
import android.widget.ImageView;

public class MyView extends ImageView implements OnGlobalLayoutListener

{
    private int radius = 0;
    
    private RectF rectF = null;
    
    private test.bg.OnTouchListener mOnTouchListener=null;
    
    public MyView(Context context)
    {
        super(context);
        TypedArray ta = context.obtainStyledAttributes(R.styleable.MyView);
        radius = ta.getDimensionPixelSize(R.styleable.MyView_radius, 0);
        rectF = new RectF(0, 0, 2 * radius, 2 * radius);
        ta.recycle();
        
        ViewTreeObserver vto = getViewTreeObserver();
        vto.addOnGlobalLayoutListener(this);
    }
    
    public MyView(Context context, AttributeSet attrs, int defStyle)
    {
        super(context, attrs, defStyle);
        TypedArray ta = context.obtainStyledAttributes(attrs,
                R.styleable.MyView);
        radius = ta.getDimensionPixelSize(R.styleable.MyView_radius, 0);
        rectF = new RectF(0, 0, 2 * radius, 2 * radius);
        ta.recycle();
        
        ViewTreeObserver vto = getViewTreeObserver();
        vto.addOnGlobalLayoutListener(this);
    }
    
    public MyView(Context context, AttributeSet attrs)
    {
        super(context, attrs);
        TypedArray ta = context.obtainStyledAttributes(attrs,
                R.styleable.MyView);
        radius = ta.getDimensionPixelSize(R.styleable.MyView_radius, 0);
        rectF = new RectF(0, 0, 2 * radius, 2 * radius);
        ta.recycle();
        
        ViewTreeObserver vto = getViewTreeObserver();
        vto.addOnGlobalLayoutListener(this);
    }
    
    public void setOnTouchListener(test.bg.OnTouchListener mOnTouchListener){
        this.mOnTouchListener=mOnTouchListener;
    }
    @Override
    protected void onDraw(Canvas canvas)
    {
        Paint p = new Paint();
        p.reset();
        p.setARGB(255, 255, 0, 0);
        canvas.drawRoundRect(rectF, radius, radius, p);
        super.onDraw(canvas);
    }
    
    @Override
    public void onGlobalLayout()
    {
        LayoutParams lp = getLayoutParams();
        lp.height = 2 * radius;
        lp.width = 2 * radius;
        setLayoutParams(lp);
    }
    
    @Override
    public boolean onTouchEvent(MotionEvent event)
    {
        float x = event.getX();
        float y = event.getY();
        
        if ((x-radius)*(x-radius)+(y-radius)*(y-radius)<radius*radius)
        {
            Log.d("nei", ""+x+":"+y);
            return mOnTouchListener.onTouchEvent(this, event);
        }
        else
        {
            Log.d("wai", ""+x+":"+y);
            return false;
        }
    }
}

其中TypedArray ta = context.obtainStyledAttributes(R.styleable.MyView);
        radius = ta.getDimensionPixelSize(R.styleable.MyView_radius, 0);

涉及到的代码事先在res/valus下新建attrs.xml并加入内容

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <declare-styleable name="MyView">  
        <attr name="radius" format="dimension" />  
    </declare-styleable>
</resources>

即定义了属性和属性类型，在布局文件设置属性时需要加入xmlns:gain="http://schemas.android.com/apk/res/test.bg"，其中gain是属性的前缀，test.bg是包名，完整布局文件如下

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:gain="http://schemas.android.com/apk/res/test.bg"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="vertical" >

    <test.bg.MyView
        android:id="@+id/mv"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        gain:radius="160dp"
        android:src="@drawable/ic_launcher" >
    </test.bg.MyView>

</LinearLayout>

接下就可以直接用MyView了，代码如下

package test.bg;

import android.app.Activity;
import android.os.Bundle;
import android.view.MotionEvent;
import android.view.View;
import android.widget.Toast;

public class TestBgActivity extends Activity implements OnTouchListener
{
    MyView mv;
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        
        setContentView(R.layout.main);
        MyView mv = (MyView) findViewById(R.id.mv);
        mv.setOnTouchListener(this);
    }
    
    @Override
    public boolean onTouchEvent(View v, MotionEvent event)
    {
        if (v.getId() == R.id.mv)
        {
            Toast.makeText(this,
                    "haha:" + v.getId() + ":" + event.getX() + ":"
                            + event.getY(),
                    Toast.LENGTH_SHORT).show();
        }
        return false;
    }
}

注意到这里的OnTouchListener并不是系统的OnTouchListener，而是我们自己定义的一个，只不过名称相同而已，定义如下

package test.bg;

import android.view.MotionEvent;
import android.view.View;


public interface OnTouchListener
{
    public boolean onTouchEvent(View v, MotionEvent event);
}

为什么要自己定义OnTouchListener？因为android的传统控件都是都是以矩形区域来响应事件的，而自定义的控件可以根据自己需要的形状来响应事件，比如本例的圆形事件区响应，而不在圆内，即使是在圆的外接矩形内也不能响应，因为我们在MyView里面实现了View的onTouchEvent(MotionEvent event)方法从而进行过滤，即代码

 @Override
    public boolean onTouchEvent(MotionEvent event)
    {
        float x = event.getX();
        float y = event.getY();
        
        if ((x-radius)*(x-radius)+(y-radius)*(y-radius)<radius*radius)
        {
            Log.d("nei", ""+x+":"+y);
            return mOnTouchListener.onTouchEvent(this, event);
        }
        else
        {
            Log.d("wai", ""+x+":"+y);
            return false;
        }
    }

即事件发生在圆内就触发自定义方法，圆外的直接忽略。

That's all！nice day，isn't it？