Andriod Studio学习笔记第九天

底部导航的实现（BottomNavigationView使用练习）
一、简述：
1.创建一个菜单Menu，添加Bottom的四个Item。
2.创建四个LayoutXML，并用Fragment加载。
3.主界面：ViewPager+BottomNavigationView，BottomNavigationView静态调用Menu，ViewPager动态调用4个Fragment。
4.主程序：创建FragmentPagerAdapter类，添加4个Fragment；覆写onNavigationItemSelected方法，Item选中时，改变ViewPager ；viewpager改变的监听事件，ViewPager改变时改变对应的Item。
二、具体实现：
1.创建一个菜单Menu，添加Bottom的四个Item。

<?xml version="1.0" encoding="utf-8"?>
<menu xmlns:android="http://schemas.android.com/apk/res/android">
    <item
        android:id="@+id/item1"
        android:title="主界面"
        android:icon="@mipmap/ic_launcher_round"></item>
    <item
        android:id="@+id/item2"
        android:title="我"
        android:icon="@mipmap/ic_launcher"></item>
    <item
        android:id="@+id/item3"
        android:title="查看"
        android:icon="@mipmap/ic_launcher_round"></item>
    <item
        android:id="@+id/item4"
        android:title="设置"
        android:icon="@mipmap/ic_launcher"></item>

2.创建四个LayoutXML，并用Fragment加载。

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:gravity="center">

    <ImageView
        android:id="@+id/imageView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_weight="1"
        app:srcCompat="@drawable/ic_launcher_background" />
</LinearLayout>

import android.support.annotation.Nullable;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

public class MyFragment1 extends Fragment {
    @Nullable
    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        View view1 = inflater.inflate(R.layout.layout_page1,container,false);
        return view1;
    }
}

3.主界面：ViewPager+BottomNavigationView，BottomNavigationView静态调用Menu，ViewPager动态调用4个Fragment。

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <android.support.v4.view.ViewPager
        android:id="@+id/view1"
        android:layout_width="match_parent"
        android:layout_height="match_parent" >

    </android.support.v4.view.ViewPager>

    <android.support.design.widget.BottomNavigationView
        android:id="@+id/bottom1"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        app:layout_constraintBottom_toBottomOf="parent"
        app:menu="@menu/menu_main">

    </android.support.design.widget.BottomNavigationView>

</android.support.constraint.ConstraintLayout>

4.主程序：创建FragmentPagerAdapter类，添加4个Fragment；覆写onNavigationItemSelected方法，Item选中时，改变ViewPager ；viewpager改变的监听事件，ViewPager改变时改变对应的Item。

package com.example.wxt.bottomnavigation;

import android.support.annotation.NonNull;
import android.support.annotation.Nullable;
import android.support.design.widget.BottomNavigationView;
import android.support.design.widget.TabLayout;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentPagerAdapter;
import android.support.v4.view.ViewPager;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.MenuItem;

import java.util.ArrayList;
import java.util.List;

public class MainActivity extends AppCompatActivity {

    ViewPager viewPager;
    List<Fragment>fragments;
    BottomNavigationView bottomNavigationView;
    MenuItem menuItem;


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

        viewPager=findViewById(R.id.view1);
        bottomNavigationView = findViewById(R.id.bottom1);
        bottomNavigationView.setOnNavigationItemSelectedListener(new BottomNavigationView.OnNavigationItemSelectedListener() {
        //Item选中时，改变ViewPager         	
 	@Override
            public boolean onNavigationItemSelected(@NonNull MenuItem item) {
                switch(item.getItemId()){
                    case R.id.item1:
                        viewPager.setCurrentItem(0);
                        break;
                    case R.id.item2:
                        viewPager.setCurrentItem(1);
                        break;
                    case R.id.item3:
                        viewPager.setCurrentItem(2);
                        break;
                    case R.id.item4:
                        viewPager.setCurrentItem(3);
                        break;
                        default:
                            break;
                }
                return true;
            }
        });
//viewpager改变的监听事件，ViewPager改变时改变对应的Item
        viewPager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {
            @Override
            public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
            }
            @Override
            public void onPageSelected(int position) {
                if(menuItem!=null)
                {//menuItem为空，退出初始化，不选中当前Item
                    menuItem.setChecked(false);
                }
                else
                {//menuItem为空，初始化，Item设置为0
                    menuItem=bottomNavigationView.getMenu().getItem(0);
                    //选中当前Item
                    menuItem.setChecked(true);
                }
                //根据ViewPager的Position，选择Item
                menuItem=bottomNavigationView.getMenu().getItem(position);
                menuItem.setChecked(true);
            }
            @Override
            public void onPageScrollStateChanged(int state) {

            }
        });


        fragments= new ArrayList<>();
        fragments.add(new MyFragment1());
        fragments.add(new MyFragment2());
        fragments.add(new MyFragment3());
        fragments.add(new MyFragment4());
        adapter myadpter = new adapter(getSupportFragmentManager(),fragments);
        viewPager.setAdapter(myadpter);


    }

    private class adapter extends FragmentPagerAdapter{
        private List<Fragment> list;
        public adapter(FragmentManager fm,List<Fragment> list) {
            super(fm);
            this.list = list;
        }

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

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

    }
}