viewPager 的可滑动 Title

有三种方式：

1. 系统提供的title

缺点：标题在viewpager的滑动过程中也会滑动

实现：在ViewPager布局中添加 PagerTabStrip 或者是 PagerTitleStrip 即可（两者选一个）

2. 自定义 Title 布局为：多个TextView + 一个 ImageView

3. 自定义 Title 布局为：一个LinearLayout 包含多个TextView ，重写onDraw() 方法，画出滑动块

（推荐使用）

    public ViewPagerTitleView(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        this.mContext = context;
        mPaint = new Paint();
        mPaint.setColor(context.getResources().getColor(R.color.colorAccent));
        mPaint.setStyle(Paint.Style.FILL_AND_STROKE);

        mLayout = new LinearLayout(context);
        mLayout.setOrientation(LinearLayout.HORIZONTAL);
        LayoutParams params = new LinearLayout.LayoutParams(LinearLayout.LayoutParams.MATCH_PARENT, LinearLayout.LayoutParams.WRAP_CONTENT);
        params.setMargins(0, 20, 0, 20);
        addView(mLayout, params);

        params1 = new LinearLayout.LayoutParams(LinearLayout.LayoutParams.MATCH_PARENT, LinearLayout.LayoutParams.WRAP_CONTENT, 1.0f);

        setWillNotDraw(false);
    }

    public void setData() {
        for (int i = 0; i < mPager.getAdapter().getCount(); i++) {
            TextView textView = new TextView(mContext);
            textView.setTextSize(18);
            textView.setText(mPager.getAdapter().getPageTitle(i));
            textView.setGravity(Gravity.CENTER);
            textView.setLayoutParams(params1);
            final int finalI = i;
            textView.setOnClickListener(new OnClickListener() {
                @Override
                public void onClick(View v) {
                    mPager.setCurrentItem(finalI);
                }
            });
            mLayout.addView(textView);
        }
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        int width = mLayout.getWidth() / mPager.getAdapter().getCount();
        canvas.drawRect(mLayout.getLeft() + (mPosition + mDistense) * width, mLayout.getBottom(), mLayout.getLeft() + (mPosition + 1 + mDistense) * width, mLayout.getBottom() + dp(6), mPaint);
    }

    public int dp(float var0) {
        float density = 2.0f;
        return var0 == 0.0F ? 0 : (int) Math.ceil((double) (density * var0));
    }

    public void setViewPager(ViewPager pager) {
        this.mPager = pager;
        mPager.addView(new PagerTitleStrip(mContext));
        if (mPager.getAdapter() != null) {
            setData();
            mPager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {
                @Override
                public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
                    mDistense = positionOffset;
                    mPosition=position;
                    invalidate();
                }

                @Override
                public void onPageSelected(int position) {
                }

                @Override
                public void onPageScrollStateChanged(int state) {

                }
            });
        }
    }