SwitchPreference和Switch

Question

我有一个自定义开关控制类MySwitch

public class MySwitch extends RelativeLayout implements CompoundButton.OnCheckedChangeListener {
//private final Context context;
private String swKey;
private Integer swIcoOn, swIcoOff;
Switch mySW;
ImageView swIco;
SharedPreferences preferences;

public MySwitch(Context context) {
    super(context, null);
}

public MySwitch(Context context, AttributeSet attrs) {
    this(context, attrs, R.layout.my_switch);
}

public MySwitch(Context context, AttributeSet attrs, int defStyleAttr) {
    super(context, attrs, defStyleAttr);
    preferences = PreferenceManager.getDefaultSharedPreferences(context);
    LayoutInflater.from(context).inflate(defStyleAttr, this, true);
    //View.inflate(context, defStyleAttr, this);
    swIco = (ImageView) findViewById(R.id.swIcon);
    TextView myText = (TextView) findViewById(R.id.swTitle);
    TextView mySummary = (TextView) findViewById(R.id.swSummary);
    mySW = (Switch) findViewById(R.id.mySW);

    TypedArray ta = context.obtainStyledAttributes(attrs, R.styleable.MySwitch, 0, 0);
    try {
        myText.setText(ta.getString(R.styleable.MySwitch_android_title));
        mySummary.setText(ta.getString(R.styleable.MySwitch_android_summary));
        mySW.setTextOn(ta.getString(R.styleable.MySwitch_android_switchTextOn));
        mySW.setTextOff(ta.getString(R.styleable.MySwitch_android_switchTextOff));
        mySW.setOnCheckedChangeListener(this);
        swIcoOn = ta.getResourceId(R.styleable.MySwitch_icoOn, 0);
        swIcoOff = ta.getResourceId(R.styleable.MySwitch_icoOff, 0);
        swKey = ta.getString(R.styleable.MySwitch_android_key);
        update();
    } finally {
        ta.recycle();
    }
}

@Override
public void onCheckedChanged(CompoundButton compoundButton, boolean b) {
    update(b);
    SharedPreferences.Editor editor = preferences.edit();
    editor.putBoolean(swKey, b);
    editor.commit();
}

public void update(Boolean val) {
    mySW.setChecked(val);
    if(val)
        swIco.setImageResource(swIcoOn);
    else
        swIco.setImageResource(swIcoOff);
}

public void update() {
    update(preferences.getBoolean(swKey, false));
}

}

我想在SwitchPreference中重用此类中的代码，因为代码几乎相同，所以它的类是

public class MySwitchPref extends SwitchPreference{
MySwitch obj;
private SharedPreferences preferences;
public MySwitchPref(Context context, AttributeSet attrs) {
    super(context, attrs);
    //setLayoutResource(R.layout.my_switch);
    obj = new MySwitch(context,attrs);
}

@Override
protected void onBindView(View view) {
    super.onBindView(view);
    obj.update();
}

}

问题是在SwitchPreference上没有显示图标。 如何才能在SwitchPreference中显示图标？