package com.android.xiaobai;

import android.os.Bundle;
import android.support.annotation.Nullable;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentTransaction;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;

import com.ashokvarma.bottomnavigation.BottomNavigationBar;
import com.ashokvarma.bottomnavigation.BottomNavigationItem;

import java.util.ArrayList;

import fragment.ContactsFragment;
import fragment.DongtaiFragment;
import fragment.MsgFragment;

/**
 * Created by xiaobai on 2018/1/31/031.
 */

public class MessageActivity extends AppCompatActivity implements BottomNavigationBar.OnTabSelectedListener {
    private ArrayList<Fragment> fragments;
    private BottomNavigationBar bottomNavigationBar;
    private MsgFragment msgFragment;
    private ContactsFragment contactsFragment;
    private DongtaiFragment dongtaiFragment;
    private FragmentManager fragmentManager;
    private FragmentTransaction transaction;
    int lastSelectedPosition = 0;

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

        bottomNavigationBar = findViewById(R.id.bottom_navigation_bar);
        init();
    }

    private void init() {
        //要先设计模式后再添加图标！
        //设置按钮模式  MODE_FIXED表示固定   MODE_SHIFTING表示转移
        bottomNavigationBar.setMode(BottomNavigationBar.MODE_FIXED);
        //设置背景风格
        // BACKGROUND_STYLE_STATIC表示静态的
        //BACKGROUND_STYLE_RIPPLE表示涟漪的，也就是可以变化的 ，跟随setActiveColor里面的颜色变化
        bottomNavigationBar.setBackgroundStyle(BottomNavigationBar.BACKGROUND_STYLE_RIPPLE);
        //添加并设置图标、图标的颜色和文字
        bottomNavigationBar
                .addItem(new BottomNavigationItem(R.drawable.im_botton_message, "消息")).setActiveColor(R.color.blue)
                .addItem(new BottomNavigationItem(R.drawable.im_botton_contacts, "联系人")).setActiveColor(R.color.red)
                .addItem(new BottomNavigationItem(R.drawable.im_botton_dongtai, "动态")).setActiveColor(R.color.orign)
                .setFirstSelectedPosition(lastSelectedPosition )
                .initialise();

        bottomNavigationBar.setTabSelectedListener(this);
        setDefaultFragment();
    }

    //设置初始界面
    private void setDefaultFragment() {
        fragmentManager = getSupportFragmentManager();
        transaction = fragmentManager.beginTransaction();
        transaction.replace(R.id.layFrame, MsgFragment.newInstance("消息"));
        transaction.commit();
    }

    @Override
    public void onTabSelected(int position) {
        fragmentManager = getSupportFragmentManager();
        transaction = fragmentManager.beginTransaction();
        switch (position) {
            case 0:
                if (msgFragment == null) {
                    msgFragment = MsgFragment.newInstance("消息");
                }
                transaction.replace(R.id.layFrame, msgFragment);
                break;
            case 1:
                if (contactsFragment == null) {
                    contactsFragment = ContactsFragment.newInstance("联系人");
                }
                transaction.replace(R.id.layFrame, contactsFragment);
                break;
            case 2:
                if (dongtaiFragment == null) {
                    dongtaiFragment = DongtaiFragment.newInstance("动态");
                }
                transaction.replace(R.id.layFrame, dongtaiFragment);
                break;
            default:
                break;
        }
        // 事务提交
        transaction.commit();
    }

    @Override
    public void onTabUnselected(int position) {
        Log.d("dongtaiFragment", "onTabUnselected() called with: " + "position = [" + position + "]");
    }

    @Override
    public void onTabReselected(int position) {

    }
}

package fragment;

import android.os.Bundle;
import android.support.annotation.Nullable;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;

import com.android.xiaobai.R;

/**
 * Created by xiaobai on 2018/1/31/031.
 */

public class MsgFragment extends BaseFragment {
    /**
     * 标志位，标志已经初始化完成
     */
    private boolean isPrepared;
    /**
     * 是否已被加载过一次，第二次就不再去请求数据了
     */
    private boolean mHasLoadedOnce;
    TextView textView;
    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        if (mView == null) {
            // 需要inflate一个布局文件 填充Fragment
            mView = inflater.inflate(R.layout.fragment_msg, container, false);
            initView();
            isPrepared = true;
//        实现懒加载
            lazyLoad();
        }
        //缓存的mView需要判断是否已经被加过parent， 如果有parent需要从parent删除，要不然会发生这个mView已经有parent的错误。
        ViewGroup parent = (ViewGroup) mView.getParent();
        if (parent != null) {
            parent.removeView(mView);
        }

        return mView;
    }
    /**
     * 初始化控件
     */
    private void initView() {

    }

    @Override
    public void lazyLoad() {
        if (!isPrepared || !isVisible || mHasLoadedOnce) {
            return;
        }
        //填充各控件的数据
        mHasLoadedOnce = true;
    }
    public static MsgFragment newInstance(String param1) {
        MsgFragment fragment = new MsgFragment();
        Bundle args = new Bundle();
        args.putString("agrs1", param1);
        fragment.setArguments(args);
        return fragment;
    }
}

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context=".MessageActivity">

    <FrameLayout
        android:id="@+id/layFrame"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_weight="1" />

    <com.ashokvarma.bottomnavigation.BottomNavigationBar
        android:id="@+id/bottom_navigation_bar"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_gravity="bottom" />
</LinearLayout>

package fragment;

import android.support.v4.app.Fragment;
import android.view.View;


/**
 * Created by xiaobai on 2018/1/31/031.
 */

public abstract class BaseFragment extends Fragment {
    /**
     * Fragment当前状态是否可见
     */
    public boolean isVisible;

    /**
     * inflate布局文件 返回的view
     */
    public View mView;

    /**
     * 简化 findViewById
     *
     * @param viewId
     * @param <T>
     * @return
     */
    protected <T extends View> T find(int viewId) {
        return (T) mView.findViewById(viewId);
    }

    /**
     * setUserVisibleHint是在onCreateView之前调用的
     * 设置Fragment可见状态
     */
    @Override
    public void setUserVisibleHint(boolean isVisibleToUser) {
        super.setUserVisibleHint(isVisibleToUser);
        /**
         * 判断是否可见
         */
        if (getUserVisibleHint()) {
            isVisible = true;
            onVisible();
        } else {
            isVisible = false;
            onInvisible();
        }
    }

    /**
     * 可见
     */
    private void onVisible() {
        lazyLoad();
    }

    /**
     * 不可见
     */
    private void onInvisible() {
    }

    /**
     * 延迟加载
     * 子类必须重写此方法
     */
    public abstract void lazyLoad();
}

在自己项目里value文件夹中的dimens.xml里面复写fixed_height_bottom_padding（默认是10dp，值越小，间距越大。适合的模式是BottomNavigationBar.MODE_FIXED）

如果模式是BottomNavigationBar.MODE_SHIFTING也是一样，复写和修改相关的参数