自定义滑动指示器

先看效果：

通过自定义view + scrollTo实现。

ScrollLayout.java

public class ScrollLayout extends LinearLayout{
    private Scroller mScroller;

    public ScrollLayout(Context context) {
        this(context,null);
    }

    public ScrollLayout(Context context, AttributeSet attrs) {
        this(context, attrs, 0);
    }

    public ScrollLayout(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        mScroller = new Scroller(context);
    }

    public void startSrcoll(int startX,int startY,int dx,int dy) {
        mScroller.startScroll(startX, startY, dx, dy, 500);//mScroller.startScroll 并不会导致 View 立即进行scroll，它只会导致当前 View 无效，从而重新绘制
        invalidate();
    }

    @Override
    public void computeScroll() {
        if (mScroller.computeScrollOffset()) {
            scrollTo(mScroller.getCurrX(), mScroller.getCurrY());
            postInvalidate();
        }
    }
}

MainActivity.java

public class MainActivity extends AppCompatActivity implements View.OnClickListener {

    private RelativeLayout a, b, c;
    ImageView sortSelected;
    private ScrollLayout mScrollLayout;
    int barWidth = 0;
    int position = 0;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        WindowManager wm = (WindowManager) this.getSystemService(Context.WINDOW_SERVICE);
        int width = wm.getDefaultDisplay().getWidth();
        barWidth = width / 3;

        mScrollLayout = (ScrollLayout) findViewById(R.id.scroll);
        sortSelected = (ImageView) findViewById(R.id.iv_sort_selected);
        sortSelected.setLayoutParams(new LinearLayout.LayoutParams(barWidth, 8));

        a = (RelativeLayout) findViewById(R.id.a);
        b = (RelativeLayout) findViewById(R.id.b);
        c = (RelativeLayout) findViewById(R.id.c);
        a.setOnClickListener(this);
        b.setOnClickListener(this);
        c.setOnClickListener(this);

    }

    @Override
    public void onClick(View v) {
        int[] location = null;
        location = new int[2];
        sortSelected.getLocationOnScreen(location);
        switch (v.getId()) {
            case R.id.a:
                mScrollLayout.startSrcoll(-location[0], 0, (position - 0) * barWidth, 0);
                position = 0;
                break;
            case R.id.b:
                mScrollLayout.startSrcoll(-location[0], 0, (position - 1) * barWidth, 0);
                position = 1;
                break;
            case R.id.c:
                mScrollLayout.startSrcoll(-location[0], 0, (position - 2) * barWidth, 0);
                position = 2;
                break;
        }
    }
}

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/gls_sort_mode"
    android:layout_width="match_parent"
    android:layout_height="wrap_content">

    <LinearLayout
        android:id="@+id/ll_sort_layout"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="horizontal">

        <RelativeLayout
            android:id="@+id/a"
            style="@style/goods_sort_bg_style">

            <TextView
                android:id="@+id/tv_sort_price"
                style="@style/goods_sort_name_style"
                android:text="a" />
        </RelativeLayout>


        <RelativeLayout
            android:id="@+id/b"
            style="@style/goods_sort_bg_style">

            <TextView
                android:id="@+id/tv_sort_sales"
                style="@style/goods_sort_name_style"
                android:text="b" />
        </RelativeLayout>


        <RelativeLayout
            android:id="@+id/c"
            style="@style/goods_sort_bg_style">

            <TextView
                android:id="@+id/tv_sort_focus"
                style="@style/goods_sort_name_style"
                android:text="c" />
        </RelativeLayout>


    </LinearLayout>


    <com.example.rex.scrollbar.ScrollLayout
        android:id="@+id/scroll"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_below="@+id/ll_sort_layout">

        <ImageView
            android:id="@+id/iv_sort_selected"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:background="@drawable/goods_sort_selected" />
    </com.example.rex.scrollbar.ScrollLayout>

</RelativeLayout>

styles.xml

<resources>

    <!-- Base application theme. -->
    <style name="AppTheme" parent="Theme.AppCompat.Light.DarkActionBar">
        <!-- Customize your theme here. -->
        <item name="colorPrimary">@color/colorPrimary</item>
        <item name="colorPrimaryDark">@color/colorPrimaryDark</item>
        <item name="colorAccent">@color/colorAccent</item>
    </style>
    
    <style name="goods_sort_name_style">
        <item name="android:textColor">#b1b0b0</item>
        <item name="android:layout_centerInParent">true</item>
        <item name="android:layout_width">wrap_content</item>
        <item name="android:layout_height">wrap_content</item>
    </style>

    <style name="goods_sort_bg_style">
        <item name="android:clickable">true</item>
        <item name="android:layout_weight">1</item>
        <item name="android:layout_width">0dip</item>
        <item name="android:layout_height">25dp</item>
        <item name="android:gravity">center</item>
    </style>

</resources>

还有一种方式是通过不断改变之上条距离左边的位置来实现，这种方式只能在viewpager中使用。
打造史上最容易使用的Tab指示符——Indicator
界面切换时指示器跟随滑动-慕课网

扩展阅读：Android Scroller简单用法