不使用v7包，使没有文字的Switch兼容到Api16+

NoTextSwitch.java

package com.googfit.view;

import android.annotation.TargetApi;
import android.content.Context;
import android.os.Build;
import android.util.AttributeSet;
import android.widget.Switch;

import java.lang.reflect.Field;

/**
 * 至少可以兼容到api16+
 * Created by JiangSong on 2015/7/23.
 */
public class NoTextSwitch extends Switch {

    private Field mThumbWidthField;

    public NoTextSwitch(Context context) {
        super(context);
        init();
    }

    public NoTextSwitch(Context context, AttributeSet attrs) {
        super(context, attrs);
        init();
    }

    public NoTextSwitch(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        init();
    }

    @TargetApi(Build.VERSION_CODES.LOLLIPOP)
    public NoTextSwitch(Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes) {
        super(context, attrs, defStyleAttr, defStyleRes);
        init();
    }

    private boolean lessApi21() {
        return Build.VERSION.SDK_INT < Build.VERSION_CODES.LOLLIPOP;
    }

    private void init() {
        if (lessApi21()) {
            Class<Switch> switchClass = Switch.class;
            try {
                mThumbWidthField = switchClass.getDeclaredField("mThumbWidth");
                mThumbWidthField.setAccessible(true);
            } catch (NoSuchFieldException e) {
                e.printStackTrace();
                mThumbWidthField = null;
            }
        }
        setTextOn("");// 把开关文字去掉
        setTextOff("");
    }

    @Override
    public void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        if (lessApi21()) {
            int thumbWidth = getThumbDrawable().getIntrinsicWidth();
            int switchWidth = thumbWidth * 2 + getPaddingLeft() + getPaddingRight();

            // 因为文字被我们设为了“”，故switchWidth就会等于minSwitchWidth~~
            setSwitchMinWidth(switchWidth);
            // switch的宽度固定为switchWidth
            super.onMeasure(MeasureSpec.makeMeasureSpec(switchWidth, MeasureSpec.AT_MOST), heightMeasureSpec);
            // 试图用反射设置thumb的宽度
            if (mThumbWidthField != null) {
                try {
                    mThumbWidthField.set(this, thumbWidth);
                } catch (IllegalAccessException e) {
                    e.printStackTrace();
                }
            }
        } else {
            super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        }

    }

    @Override
    protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
        super.onLayout(changed, left, top, right, bottom);
    }
}