Android 底部按钮BottomNavigationView + Fragment + viewPager 的使用（一）

实现的效果，左右滑动，底部栏跟着滑动，中间加的是分帧的页面

上代码：主页面activity_main.xml

<?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:id="@+id/container"

    android:layout_width="match_parent"

    android:layout_height="match_parent"

    tools:context=".MainActivity">

    <android.support.v4.view.ViewPager

        android:id="@+id/view_pager"

        android:layout_width="match_parent"

        android:layout_weight="1"

        android:layout_height="0dp"/>

    <android.support.design.widget.BottomNavigationView

        android:id="@+id/navigation"

        android:layout_width="0dp"

        android:layout_height="wrap_content"

        android:layout_marginEnd="0dp"

        android:layout_marginStart="0dp"

        android:background="?android:attr/windowBackground"

        app:layout_constraintBottom_toBottomOf="parent"

        app:layout_constraintLeft_toLeftOf="parent"

        app:layout_constraintRight_toRightOf="parent"

        app:menu="@menu/navigation" />

</android.support.constraint.ConstraintLayout>

底部按钮栏代码：在menu 目录下，navigation.xml drawable 是图片。就不贴上去了，随便放个就行。

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

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

    <item

        android:id="@+id/navigation_home"

        android:icon="@drawable/ic_home_black_24dp"

        android:title="@string/title_home" />

    <item

        android:id="@+id/navigation_dashboard"

        android:icon="@drawable/ic_dashboard_black_24dp"

        android:title="@string/title_dashboard" />

    <item

        android:id="@+id/navigation_notifications"

        android:icon="@drawable/ic_notifications_black_24dp"

        android:title="@string/title_notifications" />

    <item

        android:id="@+id/navigation_setting"

        android:icon="@drawable/ic_notifications_black_24dp"

        android:title="@string/title_notifications" />

</menu>

然后是分帧里面的页面：page1.xml ，后面的复制前面的就行了 page2.xml page3.xml page4.xml

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

<LinearLayout

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

    android:layout_width="match_parent"

    android:layout_height="match_parent">

    <TextView

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:text="frag1"

        android:textSize="30sp"/>

    <Button

        android:id="@+id/bt"

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:text="Fragment中的按钮"

        android:textAllCaps="false"/>

</LinearLayout>

适配器代码：MyFragAdaptre.java

package action.sun.com.freagment;

import android.content.Context;

import android.support.v4.app.Fragment;

import android.support.v4.app.FragmentManager;

import android.support.v4.app.FragmentStatePagerAdapter;

import java.util.List;

public class MyFragAdapter extends FragmentStatePagerAdapter {

    Context context;

    List<Fragment> listFragment;

    public MyFragAdapter(FragmentManager fm, Context context, List<Fragment> listFragment) {

        super(fm);

        this.context = context;

        this.listFragment = listFragment;

    }

    @Override

    public Fragment getItem(int position) {

        return listFragment.get(position);

    }

    @Override

    public int getCount() {

        return listFragment.size();

    }

 }

分帧代码：

Fragment1.java 后面的复制就行 Fragment2.java  Fragment3.java  Fragment4.java

package action.sun.com.freagment;

import android.os.Bundle;

import android.support.annotation.Nullable;

import android.support.v4.app.Fragment;

import android.view.LayoutInflater;

import android.view.View;

import android.view.ViewGroup;

import android.widget.Button;

import android.widget.Toast;

public class Fragment1 extends Fragment {

    @Nullable

    @Override

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

        View view = inflater.inflate(R.layout.page1, container, false);

        Button bt = (Button) view.findViewById(R.id.bt);

        bt.setOnClickListener(new View.OnClickListener() {

            @Override

            public void onClick(View v) {

                Toast.makeText(getActivity(), "Fragment1上的按钮被点击了", Toast.LENGTH_SHORT).show();

            }

        });

        return view;

    }

}

主页面的显示代码：MainActivity.java

package action.sun.com.freagment;

import android.os.Bundle;

import android.support.annotation.NonNull;

import android.support.design.widget.BottomNavigationView;

import android.support.v4.app.Fragment;

import android.support.v4.view.ViewPager;

import android.support.v7.app.AppCompatActivity;

import android.view.MenuItem;

import android.widget.TextView;

import java.util.ArrayList;

import java.util.List;

public class MainActivity extends AppCompatActivity {

    private TextView mTextMessage;

    private static final String TAG = "MainActivity";

    ViewPager viewPager;

    BottomNavigationView navigation;//底部导航栏对象

    List<Fragment> listFragment;//存储页面对象

    @Override

    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);

        initView();//初始化

    }

    private void initView() {

        viewPager = (ViewPager) findViewById(R.id.view_pager);

        navigation = (BottomNavigationView) findViewById(R.id.navigation);

        //向ViewPager添加各页面

        listFragment = new ArrayList<>();

        listFragment.add(new Fragment1());

        listFragment.add(new Fragment2());

        listFragment.add(new Fragment3());

        listFragment.add(new Fragment4());

        MyFragAdapter myAdapter = new MyFragAdapter(getSupportFragmentManager(), this, listFragment);

        viewPager.setAdapter(myAdapter);

        //导航栏点击事件和ViewPager滑动事件,让两个控件相互关联

        navigation.setOnNavigationItemSelectedListener(new BottomNavigationView.OnNavigationItemSelectedListener() {

            @Override

            public boolean onNavigationItemSelected(@NonNull MenuItem item) {

                //这里设置为：当点击到某子项，ViewPager就滑动到对应位置

                switch (item.getItemId()) {

                    case R.id.navigation_home:

                        viewPager.setCurrentItem(0);

                        return true;

                    case R.id.navigation_dashboard:

                        viewPager.setCurrentItem(1);

                        return true;

                    case R.id.navigation_notifications:

                        viewPager.setCurrentItem(2);

                        return true;

                    case R.id.navigation_setting:

                        viewPager.setCurrentItem(3);

                        return true;

                    default:

                        break;

                }

                return false;

            }

        });

        viewPager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {

            @Override

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

                //注意这个方法滑动时会调用多次，下面是参数解释：

                //position当前所处页面索引,滑动调用的最后一次绝对是滑动停止所在页面

                //positionOffset:表示从位置的页面偏移的[0,1]的值。

                //positionOffsetPixels:以像素为单位的值，表示与位置的偏移

            }

            @Override

            public void onPageSelected(int position) {

                //该方法只在滑动停止时调用，position滑动停止所在页面位置

//                当滑动到某一位置，导航栏对应位置被按下

                navigation.getMenu().getItem(position).setChecked(true);

                //这里使用navigation.setSelectedItemId(position);无效，

                //setSelectedItemId(position)的官网原句：Set the selected

                // menu item ID. This behaves the same as tapping on an item

                //未找到原因

            }

            @Override

            public void onPageScrollStateChanged(int state) {

//这个方法在滑动是调用三次，分别对应下面三种状态

// 这个方法对于发现用户何时开始拖动，

// 何时寻呼机自动调整到当前页面，或何时完全停止/空闲非常有用。

//                state表示新的滑动状态，有三个值：

//                SCROLL_STATE_IDLE：开始滑动（空闲状态->滑动），实际值为0

//                SCROLL_STATE_DRAGGING：正在被拖动，实际值为1

//                SCROLL_STATE_SETTLING：拖动结束,实际值为2

            }

        });

    }

}