day14：ViewPager+Fragment的用法

ViewPager和Fragment结合看到很多地方在讲解，我今天也写了一个小例子，和大家分享一下，也帮助我深度理解他们的用法。
这个小案例要用到Fragment所以适配器要继承FragmentPagerAdapter。它里面要是实现二个方法：

public Fragment getItem(position){ }
这个是根据position返回一个Fragment
public int Count(){ }
这个是返回一共有几个Fragment

先看一下效果图：

1526393863618.gif

Tep1：建一个viewpager.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"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:orientation="vertical">
    <android.support.v4.view.ViewPager
        android:id="@+id/viewpager"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_weight="7">
    </android.support.v4.view.ViewPager>

    <android.support.design.widget.BottomNavigationView
        android:id="@+id/bottom"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_weight="1"
        app:menu="@layout/item" />

</LinearLayout>

这里我在最底部加了一个导航栏，不要忘了加载库文件啊！

Tep2：接着建一个item.xml文件

<?xml version="1.0" encoding="utf-8"?>
<menu xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">
    <item
        android:id="@+id/one"
        android:title="第一"/>
    <item
        android:id="@+id/two"
        android:title="第二"/>
    <item
        android:id="@+id/three"
        android:title="第三"/>

</menu>

Tep3：建立一个content.xml（content2.xml，content3.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="match_parent"
        android:layout_height="match_parent"
        android:id="@+id/content"
        android:textSize="50sp"
        android:gravity="center"
        android:background="@color/colorAccent"
        android:text="第一个fragment"/>

</LinearLayout>

其他的两个依葫芦画瓢就行了，相信大家都会的。

Tap4：建立三个Fragment类（这是三个界面）

package com.example.jiangyou.pic_watch;

import android.os.Bundle;
import android.support.annotation.NonNull;
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 Fragment1 extends Fragment {
    @Nullable
    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        View view = LayoutInflater.from(getContext()).inflate(R.layout.content,container,false);
        return view;
    }
}

其他的两个也是按照这个画一个。

Tap5：下面就要写适配器，新建一个FragmentAdapter

import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentPagerAdapter;

import java.util.List;

public class FragmentAdapter extends FragmentPagerAdapter{
    //private List<Fragment> mFragment;
    private Fragment1 fragment1;
    private Fragment2 fragment2;
    private Fragment3 fragment3;
    public FragmentAdapter(FragmentManager fm) {//这是一个内部类
        super(fm);
        fragment1 = new Fragment1();
        fragment2 = new Fragment2();
        fragment3 = new Fragment3();
    }

    @Override
    public Fragment getItem(int position) {
        Fragment fragment= null;
        switch (position){
            case 0:
                fragment = fragment1;
                break;
            case 1:
                fragment = fragment2;
                break;
            case 2:
                fragment = fragment3;
                break;
        }
        return fragment;
    }

    @Override
    public int getCount() {
        return 3;
    }
}

Tab6:在主activity写逻辑

import android.os.Bundle;
import android.os.PersistableBundle;
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.view.ViewPager;
import android.support.v7.app.AppCompatActivity;
import android.view.MenuItem;

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

public class MainViewPager extends AppCompatActivity {
    private ViewPager vp;
    @Override
    public void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.viewpager);
        FragmentAdapter fragmentAdapter= new FragmentAdapter(getSupportFragmentManager());//实例化adapter，得到fragment
        vp=(ViewPager)findViewById(R.id.viewpager);
        vp.setAdapter(fragmentAdapter);//建立连接
        final BottomNavigationView bottom = (BottomNavigationView)findViewById(R.id.bottom);
        bottom.setOnNavigationItemSelectedListener(new BottomNavigationView.OnNavigationItemSelectedListener() {//底部导航栏点击事件
            @Override
            public boolean onNavigationItemSelected(@NonNull MenuItem item) {
                switch (item.getItemId()){
                    case R.id.one:
                        vp.setCurrentItem(0);
                        break;
                    case R.id.two:
                        vp.setCurrentItem(1);
                        break;
                    case R.id.three:
                        vp.setCurrentItem(2);
                        break;
                }
                return true;
            }
        });
//viewpager监听事件，当viewpager滑动时得到对应的fragment碎片
        vp.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {
            @Override
            public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {

            }

            @Override
            public void onPageSelected(int position) {
                bottom.getMenu().getItem(position).setChecked(true);

            }

            @Override
            public void onPageScrollStateChanged(int state) {

            }
        });
    }
}