android imagebutton背景图片设置

gridview的布局xml有3个imagebutton，属性android：src="@drawable/on",(用background背景图片变形了，只能用src)，点击后图像重叠并且变形了，怎么办？

voice.xml

 <selector xmlns:android="http://schemas.android.com/apk/res/android">
    <item android:state_pressed="false"
        android:drawable="@drawable/voice_on_unpress" /> <!-- pressed -->
    <item android:state_pressed="true"
        android:drawable="@drawable/voice_on_do" /> <!-- default -->
    <item android:state_pressed="true"
        android:drawable="@drawable/voice_on_do" /> <!-- default -->
    <item
        android:drawable="@drawable/voice_on_unpress" />
</selector>


voice_press.xml
 <selector xmlns:android="http://schemas.android.com/apk/res/android">
    <item android:state_pressed="false"
        android:drawable="@drawable/voice_on_press" /> <!-- pressed -->
    <item android:state_pressed="true"
        android:drawable="@drawable/voice_on_do" /> <!-- default -->
    <item android:state_pressed="true"
        android:drawable="@drawable/voice_on_do" /> <!-- default -->
    <item
        android:drawable="@drawable/voice_on_press" />
</selector>

activity.java中

 search_voice.setOnClickListener(new View.OnClickListener() {
                    public void onClick(View arg0) {
                           if(flag){
                              Toast.makeText(getApplicationContext(), "语音开启",Toast.LENGTH_SHORT).show();
                              search_voice.setBackgroundResource(R.drawable.vocie_press);
                              flag = false;
                           }
                           else{
                               Toast.makeText(getApplicationContext(), "语音屏蔽",Toast.LENGTH_SHORT).show();
                              search_voice.setBackgroundResource(R.drawable.vocie);
                              flag = true;
                           }

                    }
                });