BottomNavigationView +fragment的使用

Android Studio 在添加Activity的时候是可以创建一些带模板的activity 的，比如自Base Activity、Empty Activity、FullScreen Activity、Bottom Navifation Activity

自己常用的就是Empty Activity ，它会自动在清单文件中注册activity和创建布局文件，当然这些都是可以选择的，今天心血来潮的创建了一个Bottom Navigation Activity 模板的类，发现了这个BottomNavigationVIew，它是Android Support Library 25.0.0 版本中，新增加了一个API，底部导航视图。

先看一下studio 模板中的代码

看一下BottomNavigationView的底部导航布局文件menu类型的哦！！！它的写法与正常的menu文件一致

Avtivity布局文件很简单：

       

这几个属性可以根据需求写在布局文件中：

app:itemIconTint : 设置菜单图标着色
app:itemTextColor : 设置菜单文本颜色
app:menu : 设置菜单
app:itemBackground : 设置导航栏的背景色

         在activity中申明控件，为BottomNavigationView添加一个条目选择监听OnNavigationItemSelectedListener，当选中的条目变化到时候，动态改变textview的值。

private BottomNavigationView.OnNavigationItemSelectedListener mOnNavigationItemSelectedListener
            = new BottomNavigationView.OnNavigationItemSelectedListener() {

        @Override
        public boolean onNavigationItemSelected(@NonNull MenuItem item) {
            switch (item.getItemId()) {
                case R.id.navigation_home:
                    mTextMessage.setText(R.string.title_home);
                    return true;
                case R.id.navigation_dashboard:
                    mTextMessage.setText(R.string.title_dashboard);
                    return true;
                case R.id.navigation_notifications:
                    mTextMessage.setText(R.string.title_notifications);
                    return true;
            }
            return false;
        }

    };

这时实现的效果就是当点击底部按钮时，TextView上的数据就是相应的去改变，很容易让我们想到大部分APP 的首页，但是首页如果只给个textview那是不可能，就想按照以往的经验去和Fragment结合使用。

         

package com.song.wallpager;

import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentActivity;
import android.support.v4.app.FragmentTransaction;
import android.os.Bundle;
import android.support.annotation.NonNull;
import android.support.design.widget.BottomNavigationView;
import android.view.MenuItem;
import android.widget.TextView;

public class MainActivity extends FragmentActivity {

    

    private Fragment1 fragment1;
    private Fragment2 fragment2;
    private Fragment3 fragment3;
    private Fragment[] fragments;
    private int lastShowFragment = 0;

    private BottomNavigationView.OnNavigationItemSelectedListener mOnNavigationItemSelectedListener
            = new BottomNavigationView.OnNavigationItemSelectedListener() {

        @Override
        public boolean onNavigationItemSelected(@NonNull MenuItem item) {
            switch (item.getItemId()) {
                case R.id.navigation_home:
                    if (lastShowFragment != 0) {
                        switchFrament(lastShowFragment, 0);
                        lastShowFragment = 0;
                    }
                    return true;
                case R.id.navigation_dashboard:
                    if (lastShowFragment != 1) {
                        switchFrament(lastShowFragment, 1);
                        lastShowFragment = 1;
                    }
                    return true;
                case R.id.navigation_notifications:
                    if (lastShowFragment != 2) {
                        switchFrament(lastShowFragment, 2);
                        lastShowFragment = 2;
                    }
                    return true;
            }
            return false;
        }

    };

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        BottomNavigationView navigation = (BottomNavigationView) findViewById(R.id.navigation);
        navigation.setOnNavigationItemSelectedListener(mOnNavigationItemSelectedListener);
        initFragments();
    }

    /**
     * 切换Fragment
     *
     * @param lastIndex 上个显示Fragment的索引
     * @param index     需要显示的Fragment的索引
     */
    public void switchFrament(int lastIndex, int index) {
        FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
        transaction.hide(fragments[lastIndex]);
        if (!fragments[index].isAdded()) {
            transaction.add(R.id.fragment_container, fragments[index]);
        }
        transaction.show(fragments[index]).commitAllowingStateLoss();
    }

    private void initFragments() {
        fragment1 = new Fragment1();
        fragment2 = new Fragment2();
        fragment3 = new Fragment3();
        fragments = new Fragment[]{fragment1, fragment2, fragment3};
        lastShowFragment = 0;
        getSupportFragmentManager()
                .beginTransaction()
                .add(R.id.fragment_container, fragment1)
                .show(fragment1)
                .commit();
    }

}