ViewPager自适应高度问题

最近在开发中有在一个界面做多组左右滑动的需求，当然平时最常见的就是利用ViewPager和Fragment结合，但是平时常见的只是在一个界面上存在一组左右滑动，且Fragment占满真个界面的情况。对于这个需求，一开始就遇到ViewPager的高度超出而没有自动适配高度的问题。不过网上很多大神已经解决了并分享了。参照：点击打开链接

记录一下，当做积累遇到的问题吧。

首先，定义一个CustomViewPager继承自ViewPager, 可以不用序列化实现Serializable，这里为了方面后面的Fragment传递参数才加的。

public class CustomViewPager extends ViewPager implements Serializable{

    private int height = 0;
    private int currPosition;

    private HashMap mChildViews = new LinkedHashMap<>();

    public CustomViewPager(Context context) {
        super(context);
    }

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

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        if (mChildViews.size() > currPosition){
            View child = mChildViews.get(currPosition);
            child.measure(widthMeasureSpec, MeasureSpec.makeMeasureSpec(0, MeasureSpec.UNSPECIFIED));
            height = child.getMeasuredHeight();
        }
        heightMeasureSpec = MeasureSpec.makeMeasureSpec(height, MeasureSpec.EXACTLY);
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
    }

    /** 通过设置LayoutParams来控制子View的高度 即重置当前位置下标（fragment）的高度*/
    public void resetHeight(int position){
        this.currPosition = position;
        if (mChildViews.size() > currPosition){
            LinearLayout.LayoutParams layoutParams = (LinearLayout.LayoutParams) getLayoutParams();
            if (layoutParams == null){
                layoutParams = new LinearLayout.LayoutParams(LinearLayout.LayoutParams.MATCH_PARENT, height);
            }

            layoutParams.height = height;

            setLayoutParams(layoutParams);
        }
    }

    public void setObjectForView(View view, int position){
        mChildViews.put(position, view);
    }
}

自定义的CustomViewPager主要是测量 ViewPager 当前下标的高度，然后通过resetHeight()方法重置其高度。setObjectForView(View, int)是在实例Fragment的时候调用，目的是与ViewPager进行绑定，然后可以重新测量高度进行自适应。

下面就是一个简单的例子，在ScrollView里面嵌套ViewPager,并且让ViewPager能够自适应高度。

public class FirstFragment extends Fragment {


    public FirstFragment() {
        // Required empty public constructor
    }

    public static FirstFragment newInstance(CustomViewPager vp){
        FirstFragment fragment = new FirstFragment();
        Bundle bundle = new Bundle();
        bundle.putSerializable("vp", vp);
        fragment.setArguments(bundle);
        return fragment;
    }


    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        return inflater.inflate(R.layout.fragment_first, container, false);
    }

    @Override
    public void onViewCreated(View view, @Nullable Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);
        if (getArguments() != null){
            CustomViewPager vp = (CustomViewPager) getArguments().getSerializable("vp");
            vp.setObjectForView(view, 0);
        }
    }

}

public class SecondFragment extends Fragment {


    public SecondFragment() {
        // Required empty public constructor
    }

    public static SecondFragment newInstance(CustomViewPager vp){
        SecondFragment fragment = new SecondFragment();
        Bundle bundle = new Bundle();
        bundle.putSerializable("vp", vp);
        fragment.setArguments(bundle);
        return fragment;
    }


    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        return inflater.inflate(R.layout.fragment_second, container, false);
    }

    @Override
    public void onViewCreated(View view, @Nullable Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);
        if (getArguments() != null){
            CustomViewPager vp = (CustomViewPager) getArguments().getSerializable("vp");
            vp.setObjectForView(view, 1);
        }
    }
}

public class MainActivity extends AppCompatActivity implements View.OnClickListener{

    private CustomViewPager mVp;
    private TextView mTitle1, mTitle2;
    private List mFragmentList = new ArrayList<>();

    private Context mContext;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        mContext = this;
        mVp = (CustomViewPager) findViewById(R.id.vp);
        mTitle1 = (TextView) findViewById(R.id.title1);
        mTitle2 = (TextView) findViewById(R.id.title2);
        mTitle1.setOnClickListener(this);
        mTitle2.setOnClickListener(this);
        mVp.setOffscreenPageLimit(2);
        mFragmentList.add(FirstFragment.newInstance(mVp));
        mFragmentList.add(SecondFragment.newInstance(mVp));
        mVp.setAdapter(new MyFragmentPagerAdapter(getSupportFragmentManager(), mFragmentList));
        mVp.resetHeight(0);
        updateTitleWithViewPager(0);
        mVp.addOnPageChangeListener(new PagerChangeListener(mVp));
    }

    private void updateTitleWithViewPager(int index){
        switch (index){
            case 0:
                mTitle1.setTextColor(ContextCompat.getColor(mContext, R.color.colorAccent));
                mTitle2.setTextColor(ContextCompat.getColor(mContext, R.color.text_666));
                mVp.setCurrentItem(0);
                break;
            case 1:
                mTitle1.setTextColor(ContextCompat.getColor(mContext, R.color.text_666));
                mTitle2.setTextColor(ContextCompat.getColor(mContext, R.color.colorAccent));
                mVp.setCurrentItem(1);
                break;
        }
    }

    @Override
    public void onClick(View view) {
        switch (view.getId()){
            case R.id.title1:
                updateTitleWithViewPager(0);
                break;

            case R.id.title2:
                updateTitleWithViewPager(1);
                break;
        }
    }


    static class MyFragmentPagerAdapter extends FragmentPagerAdapter{

        private List fragmentList;

        public MyFragmentPagerAdapter(FragmentManager fm) {
            super(fm);
        }

        public MyFragmentPagerAdapter(FragmentManager fm, List fragmentList) {
            super(fm);
            this.fragmentList = fragmentList;
        }

        @Override
        public Fragment getItem(int position) {
            return fragmentList.get(position);
        }

        @Override
        public int getCount() {
            return fragmentList.size();
        }
    }

    private class PagerChangeListener implements ViewPager.OnPageChangeListener {

        private CustomViewPager customViewPager;

        public PagerChangeListener(CustomViewPager viewPager){
            this.customViewPager = viewPager;
        }

        @Override
        public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {

        }

        @Override
        public void onPageSelected(int position) {
            customViewPager.resetHeight(position);
            updateTitleWithViewPager(position);
        }

        @Override
        public void onPageScrollStateChanged(int state) {

        }
    }

}

当然，上面提到Fragment和ViewPager通过setObjectForView进行绑定，上面用到了Fragment的传递参数方式进行绑定，从而在自定义CustomViewPager时实现了序列化接口Serializable，除了这种方式，还可以使用接口回调的方法，亦或最简单的直接使用Butterknife的发送和订阅 事件进行传递。