通过修改指示器的间距来改变TabLayout指示器的宽度

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1.写个工具类 封装：

import android.content.res.Resources;
import android.support.design.widget.TabLayout;
import android.util.TypedValue;
import android.view.View;
import android.widget.LinearLayout;

import java.lang.reflect.Field;

/**
 * Created by Sy on 2017/05/08.
 * 
 */

public class TabUtils {
    /**
    *  @param tabs TabLayout
     * @param leftDip marginLeft
     * @param rightDip marginRight
    */
    public static void setIndicator (TabLayout tabs, int leftDip, int rightDip){
        Class<?> tabLayout = tabs.getClass();
        Field tabStrip = null;
        try {
            tabStrip = tabLayout.getDeclaredField("mTabStrip");
        } catch (NoSuchFieldException e) {
            e.printStackTrace();
            return;
        }

        tabStrip.setAccessible(true);
        LinearLayout llTab = null;
        try {
            llTab = (LinearLayout) tabStrip.get(tabs);
        } catch (IllegalAccessException e) {
            e.printStackTrace();

         return；
        }

        int left = (int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, leftDip, Resources.getSystem().getDisplayMetrics());
        int right = (int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, rightDip, Resources.getSystem().getDisplayMetrics());

        for (int i = 0; i < llTab.getChildCount(); i++) {
            View child = llTab.getChildAt(i);
            child.setPadding(0, 0, 0, 0);
            LinearLayout.LayoutParams params = new LinearLayout.LayoutParams(0, LinearLayout.LayoutParams.MATCH_PARENT, 1);
            params.leftMargin = left;
            params.rightMargin = right;
            child.setLayoutParams(params);
            child.invalidate();
        }
    }
}

2.在Activity调用

tab_view.post(new Runnable() {
    @Override
    public void run() {
        TabUtils.setIndicator(tab_view,10,10);
    }
});

3,此方法是通过反射获取tablayout私有属性进修改属性值，如果app启动混淆 会报NoSuchFieldException；

解决方案：在proguard-rules.pro混淆文件中添加-keep class android.support.design.widget.TabLayout{*;}