实现android上方的导航条

整理自：
http://www.cnblogs.com/JohnTsai/p/4715454.html

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直接切入正题，如果我们要实现下面这两种效果该怎么做呢？

1

2

第一种效果还算比较简单，使用ViewPager再加上FragmentPagerAdapter就可以实现，其中，这其中最麻烦的就是tab下面那个导航条，需要根据屏幕大小以及标签个数来动态设置其位置
而第二种效果除了导航条的位置的变换，其长度以及tab的位置都需要仔细地去考虑···真的是非常麻烦

之前一直想着自己能不能对这种效果进行封装，但是现在谷歌自己以及发布了一个库-TabLayout，可以直接实现这样的效果啦。这个TabLayout的具体知识就不在这说了，网上有很多资料。

最后附上如果是自己实现第一种那样的效果怎么做：
因为自己实现不是我们这里的重点，所以我就直接将代码发上来就不解释了

public class MySongFrag extends Fragment {
    @BindView(R.id.view_pager)
    ViewPager viewPager;
    @BindView(R.id.tv_album)
    TextView tvAlbum;
    @BindView(R.id.tv_singer)
    TextView tvSinger;
    @BindView(R.id.tv_song)
    TextView tvSong;
    @BindView(R.id.iv_tab_line)
    ImageView ivTabLine;
    @BindView(R.id.layout_tab)
    LinearLayout tabLayout;

    ResourceUtils resourceUtils;


    FragmentPagerAdapter fragmentPagerAdapter;
    List fragmentList=new ArrayList();

    //当前显示页面的下标
    double currentIndex;
    //屏幕宽度
    double screenWidth;
    //上面的那个tab的宽度，是屏幕宽度的六分之四
    double tabWidth;
    //屏幕宽度的六分之一
    double sixInOne;

    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        View view=inflater.inflate(R.layout.frag_my_song,null);
        ButterKnife.bind(this,view);

        init();
        initTabWidth();
        initViewPager();

        return view;
    }

    private void init() {
        resourceUtils=new ResourceUtils(getActivity());
    }

    //设置上面tab宽度为屏幕宽度三分之二
    private void initTabWidth() {
        screenWidth=getActivity().getWindowManager().getDefaultDisplay().getWidth();
        tabWidth=screenWidth*2/3;
        sixInOne=screenWidth/6;

        LinearLayout.LayoutParams lp= (LinearLayout.LayoutParams) tabLayout.getLayoutParams();
        lp.width= (int) tabWidth;
        tabLayout.setLayoutParams(lp);

        LinearLayout.LayoutParams lpIv= (LinearLayout.LayoutParams) ivTabLine.getLayoutParams();
        lpIv.width=(int) tabWidth/3;
        lpIv.leftMargin=(int) sixInOne;
        ivTabLine.setLayoutParams(lpIv);
    }

    private void initViewPager() {
        SongFrag songFrag=new SongFrag();
        SingerFrag singerFrag=new SingerFrag();
        AlbumFrag albumFrag=new AlbumFrag();

        fragmentList.add(songFrag);
        fragmentList.add(singerFrag);
        fragmentList.add(albumFrag);

        fragmentPagerAdapter=new FragmentPagerAdapter(getFragmentManager()) {
            @Override
            public Fragment getItem(int position) {
                return fragmentList.get(position);
            }

            @Override
            public int getCount() {
                return fragmentList.size();
            }
        };
        viewPager.setAdapter(fragmentPagerAdapter);
        viewPager.setCurrentItem(0);
        viewPager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {
            @Override
            public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
                LinearLayout.LayoutParams lp = (LinearLayout.LayoutParams) ivTabLine
                        .getLayoutParams();


                /**
        
                 * 利用currentIndex(当前所在页面)和position(下一个页面)以及offset来
                 * 设置mTabLineIv的左边距 滑动场景：
                 * 记3个页面,
                 * 从左到右分别为0,1,2
                 * 0->1; 1->2; 2->1; 1->0
                 */
                if (currentIndex == 0 && position == 0)// 0->1
                {
                    lp.leftMargin = (int) (sixInOne+positionOffset * (tabWidth * 1.0 / 3) + currentIndex
                            * (tabWidth / 3));
                } else if (currentIndex == 1 && position == 0) // 1->0
                {
                    lp.leftMargin = (int) (-(1 - positionOffset)
                            * (tabWidth * 1.0 / 3)+sixInOne + currentIndex
                            * (tabWidth / 3));

                } else if (currentIndex == 1 && position == 1) // 1->2
                {
                    lp.leftMargin = (int) (positionOffset * (tabWidth * 1.0 / 3) + sixInOne+currentIndex
                            * (tabWidth / 3));

                } else if (currentIndex == 2 && position == 1) // 2->1
                {
                    lp.leftMargin = (int) (-(1 - positionOffset)
                            * (tabWidth * 1.0 / 3) +sixInOne+ currentIndex
                            * (tabWidth / 3));
                }
                ivTabLine.setLayoutParams(lp);
            }

            @Override
            public void onPageSelected(int position) {
                resetTextView();
                switch (position) {
                    case 0:
                        tvSong.setTextColor(resourceUtils.getColorIntRes(R.color.myColorAccent));
                        break;
                    case 1:
                        tvSinger.setTextColor(resourceUtils.getColorIntRes(R.color.myColorAccent));
                        break;
                    case 2:
                        tvAlbum.setTextColor(resourceUtils.getColorIntRes(R.color.myColorAccent));
                        break;
                }
                currentIndex = position;
            }

            @Override
            public void onPageScrollStateChanged(int state) {

            }
        });

    }

    private void resetTextView() {
        tvAlbum.setTextColor(resourceUtils.getColorIntRes(R.color.tab_text_unchecked));
        tvSinger.setTextColor(resourceUtils.getColorIntRes(R.color.tab_text_unchecked));
        tvSong.setTextColor(resourceUtils.getColorIntRes(R.color.tab_text_unchecked));

    }
}