android.support.v4.app.Fragment;

android.support.v4.app.FragmentActivity;

android.support.v4.app.FragmentManager;

android.support.v4.app.FragmentPagerAdapter;

android.support.v4.app.FragmentStatePagerAdapter;

android.support.v4.view.PagerAdapter;

android.support.v4.view.ViewPager;

android.support.v4.view.ViewPager.OnPageChangeListener;

Called when the host view is attempting to determine确定 if an item's position has changed. Returns POSITION_UNCHANGED if the position of the given item has not changed or POSITION_NONE if the item is no longer present存在 in the adapter.

The default implementation assumes that items will never change position and always returns POSITION_UNCHANGED.

@param object Object representing an item, previously returned by a call to instantiateItem(View, int).

@return object's new position index from [0, getCount()-1], POSITION_UNCHANGED if the object's position has not changed, or POSITION_NONE if the item is no longer present.

public int getItemPosition(@NonNull Object object) {

    return POSITION_UNCHANGED;

}

Create the page for the given position.

The adapter is responsible负责 for adding the view to the container given here, although it only must ensure this is done by the time it returns from finishUpdate(ViewGroup).

@param container The containing View in which the page will be shown.

@param position The page position to be instantiated.

@return Returns an Object representing the new page. This does not need to be a View, but can be some other container of the page.

public Object instantiateItem(ViewGroup container, int position) {

    return instantiateItem((View) container, position);

}

public Object instantiateItem(View container, int position) {

    throw new UnsupportedOperationException("Required method instantiateItem was not overridden");

}

Remove a page for the given position.

The adapter is responsible负责 for removing the view from its container, although it only must ensure this is done by the time it returns from finishUpdate(ViewGroup).

@param container The containing View from which the page will be removed.

@param position The page position to be removed.

@param object The same object that was returned by instantiateItem(View, int).

public void destroyItem(ViewGroup container, int position, Object object) {

    destroyItem((View) container, position, object);

}

public void destroyItem(View container, int position, Object object) {

    throw new UnsupportedOperationException("Required method destroyItem was not overridden");

}

//Return the Fragment associated with a specified position.

public abstract Fragment getItem(int position);

public Object instantiateItem(ViewGroup container, int position) {

    if (mCurTransaction == null) mCurTransaction = mFragmentManager.beginTransaction();

    final long itemId = getItemId(position);

    // Do we already have this fragment?

    String name = makeFragmentName(container.getId(), itemId);

    Fragment fragment = mFragmentManager.findFragmentByTag(name);

    if (fragment != null) {

        mCurTransaction.attach(fragment); //非首次初始化为attach

    } else {

        fragment = getItem(position); //首次初始化为add

        mCurTransaction.add(container.getId(), fragment, makeFragmentName(container.getId(), itemId));

    }

    if (fragment != mCurrentPrimaryItem) {

        fragment.setMenuVisibility(false);

        FragmentCompat.setUserVisibleHint(fragment, false); //非常重要的 setUserVisibleHint 冒出来了

    }

    return fragment;

}

public void destroyItem(@NonNull ViewGroup container, int position, @NonNull Object object) {

    if (this.mCurTransaction == null) {

        this.mCurTransaction = this.mFragmentManager.beginTransaction();

    }

    this.mCurTransaction.detach((Fragment)object); //为毛要调用detach？

}

public void destroyItem(ViewGroup container, int position, Object object) {

    Fragment fragment = (Fragment) object;

    if (mCurTransaction == null) mCurTransaction = mFragmentManager.beginTransaction();

    while (mSavedState.size() <= position) {

        mSavedState.add(null);

    }

    mSavedState.set(position, fragment.isAdded() ? mFragmentManager.saveFragmentInstanceState(fragment) : null);

    mFragments.set(position, null);

    mCurTransaction.remove(fragment); //移除

}

private int mOffscreenPageLimit = DEFAULT_OFFSCREEN_PAGES;

public void setOffscreenPageLimit(int limit) {

    if (limit < 1) {

        Log.w("ViewPager", "Requested offscreen page limit " + limit + " too small; defaulting to " + 1);

        limit = 1;

    }

    if (limit != this.mOffscreenPageLimit) {

        this.mOffscreenPageLimit = limit;

        this.populate();

    }

}

class ViewPagerAdapter extends PagerAdapter {

    @Override

    public int getCount() {

        int size = anchorList.size();

        return size % 3 == 0 ? size / 3 : (size / 3 + 1);

    }

    @Override

    public int getItemPosition(Object object) {

        return POSITION_NONE;  // -2

    }

    @Override

    public void destroyItem(ViewGroup container, int position, Object object) {

        container.removeView((View) object);

    }

    @Override

    public Object instantiateItem(ViewGroup container, int position) {

        LinearLayout linearLayout;

        firstBean = anchorList.get(3 * position + 0); //第一个子View的数据

        secondBean = anchorList.get(3 * position + 1); //第二个子View的数据

        thirdBean = anchorList.get(3 * position + 2); //第三个子View的数据

        container.addView(linearLayout);

        return linearLayout;

    }

    @Override

    public boolean isViewFromObject(View view, Object object) {

        return view == object;

    }

}

@Override

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

    //参数为：当前条目位置，当前条目移动的百分比(0-100%)，移动距离(0-item的width)

    int leftMargin; //小红点动态移动的距离

    //最后一个条目时，不再继续向后移动

    if (position == mList.size() - 1) {

        leftMargin = position * mPointWidth + MARGIN_BETWEEN_POINTS;

    } else {

        leftMargin = (int) (mPointWidth * positionOffset) + position * mPointWidth + MARGIN_BETWEEN_POINTS;

    }

    RelativeLayout.LayoutParams params = (RelativeLayout.LayoutParams) view_red_point.getLayoutParams();

    params.leftMargin = leftMargin;

    view_red_point.setLayoutParams(params);

}

@Override

public void onPageSelected(int position) {

    tv_right.setTextColor(Color.GRAY);//根据位置设置字体颜色

    tv_left.setTextColor(Color.RED);

    Animation animation = new TranslateAnimation(currIndex * one, position * one, 0, 0);

    currIndex = position; //将当前位置设置为目标位置

    animation.setFillAfter(true);//停留在动画结束时的状态

    animation.setDuration(100);//动画切换时间

    iv_red.startAnimation(animation); //根据当前位置和将要移动到的位置创建动画

}

public class MainActivity extends FragmentActivity {

    private ViewPager mViewPager;

    private TextView tvTitle, tvWeixin, tvFriend, tvContact, tvSetting;

    private String[] titles = {"微信", "通讯录", "发现", "我"};

    @Override

    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);

        initView();

        mViewPager.setAdapter(getPagerAdapter(2));

        mViewPager.addOnPageChangeListener(new MyOnPageChangeListener());

        //mViewPager.setOffscreenPageLimit(titles.length - 1); //这个方法的杀伤力巨大，岂会导致所有缓存的Fragment都不会被销毁掉

        reset(tvWeixin, 0); // 使用 mViewPager.setCurrentItem(0); 并不会回调 onPageSelected

    }

    private PagerAdapter getPagerAdapter(int type) {

        switch (type) {

            case 0:

                return new MyPagerAdapter();

            case 1:

                return new MyFragmentPagerAdapter(getSupportFragmentManager());

            case 2:

                return new MyFragmentStatePagerAdapter(getSupportFragmentManager());

            default:

                return new MyPagerAdapter();

        }

    }

    private void initView() {

        mViewPager = findViewById(R.id.id_viewpager);

        tvTitle = findViewById(R.id.tv_title);

        tvWeixin = findViewById(R.id.tv_tab_bottom_weixin);

        tvFriend = findViewById(R.id.tv_tab_bottom_friend);

        tvContact = findViewById(R.id.tv_tab_bottom_contact);

        tvSetting = findViewById(R.id.tv_tab_bottom_setting);

        tvTitle.setOnClickListener(v -> {

            for (Fragment fragment : getSupportFragmentManager().getFragments()) {

                Log.i("bqt", "【Fragment】" + ((SimpleTabFragment) fragment).getName());

            }

        });

        tvWeixin.setOnClickListener(v -> reset(v, 0));

        tvFriend.setOnClickListener(v -> reset(v, 1));

        tvContact.setOnClickListener(v -> reset(v, 2));

        tvSetting.setOnClickListener(v -> reset(v, 3));

    }

    private void reset(View v, int position) {

        tvWeixin.setSelected(false);

        tvFriend.setSelected(false);

        tvContact.setSelected(false);

        tvSetting.setSelected(false);

        v.setSelected(true);

        mViewPager.setCurrentItem(position);

        tvTitle.setText(titles[position]);

    }

    class MyPagerAdapter extends PagerAdapter {

        @Override

        public boolean isViewFromObject(@NonNull View view, @NonNull Object object) {

            Log.i("bqt", "【isViewFromObject】");

            return view == object;

        }

        @Override

        public int getCount() {

            return titles.length;

        }

        @NonNull

        public Object instantiateItem(@NonNull ViewGroup container, int position) {

            Log.i("bqt", "【PagerAdapter-instantiateItem】" + position); //这个并非抽象方法

            TextView tv = new TextView(container.getContext());

            tv.setText(titles[position] + "：" + new SimpleDateFormat("HH:mm:ss SSS", Locale.getDefault()).format(new Date()));

            tv.setBackgroundColor(0xFF000000 + new Random().nextInt(0xFFFFFF));

            container.addView(tv);

            return tv;

        }

        public void destroyItem(@NonNull ViewGroup container, int position, @NonNull Object object) {

            Log.i("bqt", "【destroyItem】" + position); //这个并非抽象方法

            container.removeView((View) object);

        }

    }

    class MyFragmentPagerAdapter extends FragmentPagerAdapter {

        MyFragmentPagerAdapter(FragmentManager fm) {

            super(fm);

        }

        @Override

        public Fragment getItem(int position) {

            Log.i("bqt", "【----------------FragmentPagerAdapter-getItem:" + position + "----------------】");

            return SimpleTabFragment.newInstance(titles[position]);

        }

        @Override

        public int getCount() {

            return titles.length;

        }

    }

    class MyFragmentStatePagerAdapter extends FragmentStatePagerAdapter {

        MyFragmentStatePagerAdapter(FragmentManager fm) {

            super(fm);

        }

        @Override

        public int getCount() {

            return titles.length;

        }

        @Override

        public Fragment getItem(int position) {

            Log.i("bqt", "【----------------FragmentStatePagerAdapter-getItem:" + position + "----------------】");

            return SimpleTabFragment.newInstance(titles[position]);

        }

    }

    class MyOnPageChangeListener implements OnPageChangeListener {

        @Override

        public void onPageScrolled(int i, float v, int i1) {

        }

        @Override

        public void onPageSelected(int position) {

            Log.i("bqt", "【onPageSelected】" + position);

            switch (position) {

                case 0:

                    reset(tvWeixin, position);

                    break;

                case 1:

                    reset(tvFriend, position);

                    break;

                case 2:

                    reset(tvContact, position);

                    break;

                case 3:

                    reset(tvSetting, position);

                    break;

                default:

                    break;

            }

        }

        @Override

        public void onPageScrollStateChanged(int i) {

        }

    }

}

public class SimpleTabFragment extends Fragment {

    private String name;

    public static final String ARGUMENT = "name";

    public static SimpleTabFragment newInstance(String name) {

        SimpleTabFragment fragment = new SimpleTabFragment();

        Bundle bundle = new Bundle();

        bundle.putString(ARGUMENT, name);

        fragment.setArguments(bundle);

        return fragment;

    }

    public SimpleTabFragment() {

        Log.i("bqt", "【----------------构造方法" +hashCode() +"----------------】");

    }

    @Override

    public void onAttach(Context context) {

        super.onAttach(context);

        Log.i("bqt", "【--------onAttach--------】");

    }

    @Override

    public void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        Bundle bundle = getArguments();

        name = bundle != null ? bundle.getString(ARGUMENT) : "unknown";

        Log.i("bqt", "【--------onCreate:" + name + "--------】");

    }

    @Override

    public View onCreateView(@NonNull LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {

        Log.i("bqt", "【----onCreateView" + name + "----】");

        View view = inflater.inflate(R.layout.fragment_tab, container, false);

        TextView tv = view.findViewById(R.id.tv);

        tv.setText(name + "：" + new SimpleDateFormat("HH:mm:ss SSS", Locale.getDefault()).format(new Date()));

        tv.setBackgroundColor(0xFF000000 + new Random().nextInt(0xFFFFFF));

        return view;

    }

    @Override

    public void onResume() {

        super.onResume();

        Log.i("bqt", "【onResume:" + name + "】");

    }

    @Override

    public void onDestroyView() {

        super.onDestroyView();

        Log.i("bqt", "【----onDestroyView:" + name + "------】");

    }

    @Override

    public void onDestroy() {

        super.onDestroy();

        Log.i("bqt", "【--------onDestroy:" + name + "--------】");

    }

    @Override

    public void onDetach() {

        super.onDetach();

        Log.i("bqt", "【--------onDetach:" + name + "--------】");

    }

    public void setName(String name) {

        this.name = name;

    }

    public String getName() {

        return name;

    }

}

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"

              android:layout_width="match_parent"

              android:layout_height="match_parent"

              android:orientation="vertical">

    <TextView

        android:id="@+id/tv_title"

        android:layout_width="fill_parent"

        android:layout_height="45dp"

        android:gravity="center"

        android:text="微信"

        android:textColor="#000"

        android:textSize="20sp"

        android:textStyle="bold"/>

    <View

        android:layout_width="match_parent"

        android:layout_height="1px"

        android:background="#dbdbdb"/>

    <android.support.v4.view.ViewPager

        android:id="@+id/id_viewpager"

        android:layout_width="fill_parent"

        android:layout_height="0dp"

        android:layout_weight="2016"/>

    <View

        android:layout_width="match_parent"

        android:layout_height="1px"

        android:background="#dbdbdb"/>

    <LinearLayout

        android:id="@+id/ly_main_tab_bottom"

        android:layout_width="fill_parent"

        android:layout_height="55dp">

        <TextView

            android:id="@+id/tv_tab_bottom_weixin"

            android:layout_width="0dp"

            android:layout_height="fill_parent"

            android:layout_weight="1"

            android:gravity="center"

            android:text="微信"

            android:textColor="@drawable/text_color_sel"/>

        <TextView

            android:id="@+id/tv_tab_bottom_friend"

            android:layout_width="0dp"

            android:layout_height="fill_parent"

            android:layout_weight="1"

            android:gravity="center"

            android:text="通讯录"

            android:textColor="@drawable/text_color_sel"/>

        <TextView

            android:id="@+id/tv_tab_bottom_contact"

            android:layout_width="0dp"

            android:layout_height="fill_parent"

            android:layout_weight="1"

            android:gravity="center"

            android:text="发现"

            android:textColor="@drawable/text_color_sel"/>

        <TextView

            android:id="@+id/tv_tab_bottom_setting"

            android:layout_width="0dp"

            android:layout_height="fill_parent"

            android:layout_weight="1"

            android:gravity="center"

            android:text="我"

            android:textColor="@drawable/text_color_sel"/>

    </LinearLayout>

</LinearLayout>

<?xml version="1.0" encoding="utf-8"?>

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"

              android:layout_width="fill_parent"

              android:layout_height="fill_parent"

              android:orientation="vertical">

    <TextView

        android:id="@+id/tv"

        android:layout_width="fill_parent"

        android:layout_height="fill_parent"

        android:gravity="center"

        android:text="第一个页面"

        android:textColor="#000"

        android:textSize="20sp"/>

</LinearLayout>

【----------------FragmentPagerAdapter-getItem:0----------------】

【----------------构造方法215908580----------------】

【----------------FragmentPagerAdapter-getItem:1----------------】

【----------------构造方法173705549----------------】

【--------onAttach--------】

【--------onCreate:微信--------】

【--------onAttach--------】

【--------onCreate:通讯录--------】

【----onCreateView微信----】

【onResume:微信】

【----onCreateView通讯录----】

【onResume:通讯录】

【onPageSelected】1

【----------------FragmentPagerAdapter-getItem:2----------------】

【----------------构造方法88702934----------------】

【--------onAttach--------】

【--------onCreate:发现--------】

【----onCreateView发现----】

【onResume:发现】

【onPageSelected】0

【----onDestroyView:发现------】

【onPageSelected】0

【----onDestroyView:发现------】

【--------onDestroy:发现--------】

【--------onDetach:发现--------】

【onResume:微信】

【onResume:通讯录】

【onPageSelected】1

【----onCreateView发现----】

【onResume:发现】

【onPageSelected】1

【----------------FragmentStatePagerAdapter-getItem:2----------------】

【----------------构造方法62405875----------------】

【--------onAttach--------】

【--------onCreate:发现--------】

【----onCreateView发现----】

【onResume:发现】

【----onDestroyView:微信------】

【--------onDestroy:微信--------】

【--------onDetach:微信--------】

【----onDestroyView:通讯录------】

【--------onDestroy:通讯录--------】

【--------onDetach:通讯录--------】

【----onDestroyView:发现------】

【--------onDestroy:发现--------】

【--------onDetach:发现--------】

【----------------构造方法207117498----------------】

【----------------构造方法264001387----------------】

【----------------构造方法227934920----------------】

【--------onAttach--------】

【--------onCreate:微信--------】

【--------onAttach--------】

【--------onCreate:通讯录--------】

【--------onAttach--------】

【--------onCreate:发现--------】

【----onCreateView微信----】

【----onCreateView通讯录----】

【----onCreateView发现----】

【onPageSelected】1

【onResume:微信】

【onResume:通讯录】

【onResume:发现】

【----onDestroyView:微信------】

【--------onDestroy:微信--------】

【--------onDetach:微信--------】

【----onDestroyView:通讯录------】

【--------onDestroy:通讯录--------】

【--------onDetach:通讯录--------】

//注意，这里并不会调用第三个Fragment的onDestroyView，因为这个Fragment的View早就被销毁了

【--------onDestroy:发现--------】

【--------onDetach:发现--------】

【----------------构造方法262171070----------------】

【----------------构造方法242817567----------------】

【----------------构造方法41927020----------------】

【--------onAttach--------】

【--------onCreate:微信--------】

【--------onAttach--------】

【--------onCreate:通讯录--------】

【--------onAttach--------】

【--------onCreate:发现--------】

【----onCreateView微信----】

【----onCreateView通讯录----】

//同样，这里并不会调用第三个Fragment的onCreateView，因为这个Fragment的View目前并不需要创建

【onResume:微信】

【onResume:通讯录】

【----onDestroyView:微信------】

【--------onDestroy:微信--------】

【--------onDetach:微信--------】

【----onDestroyView:通讯录------】

【--------onDestroy:通讯录--------】

【--------onDetach:通讯录--------】

//这里完全没有调用第三个Fragment的任何回调方法，因为在切换到第一个Fragment时，第三个Fragment已经完全销毁了

【----------------构造方法41927020----------------】

【----------------构造方法48001845----------------】

//这里也不会重新创建第三个Fragment

【--------onAttach--------】

【--------onCreate:微信--------】

【--------onAttach--------】

【--------onCreate:通讯录--------】

【----onCreateView微信----】

【----onCreateView通讯录----】

【onResume:微信】

【onResume:通讯录】