dpdb/code/main/java/com/example/dxsdpdb/MainActivity.java

package com.example.dxsdpdb;

import android.os.Bundle;
import android.view.View;
import android.widget.LinearLayout;

import androidx.appcompat.app.AppCompatActivity;
import androidx.fragment.app.Fragment;
import androidx.fragment.app.FragmentManager;
import androidx.fragment.app.FragmentTransaction;

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

public class MainActivity extends AppCompatActivity {

    private List<Fragment> mFragments;

    private LinearLayout mIndexPage;
    private LinearLayout mMissionPage;
    private LinearLayout mMinePage;

//    private ImageButton mImgIndexPage;
//    private ImageButton mImgMissionPage;
//    private ImageButton mImgMinePage;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        //去除标题栏
        getSupportActionBar().hide();
        setContentView(R.layout.activity_main);
        initFragments(); //初始化数据
        initViews(); //初始化控件
        initEvents(); //初始化事件
        initFirstRun(0);//第一次运行初始化界面，第一个碎片
    }

    private void initFragments() {
        mFragments = new ArrayList<>();
        //将四个 Fragment 加入集合中
        mFragments.add(new IndexFragment());
        mFragments.add(new MissionFragment());
        mFragments.add(new MineFragment());
    }

    private void initViews() {
        mIndexPage = (LinearLayout) findViewById(R.id.id_index);
        mMissionPage = (LinearLayout) findViewById(R.id.id_tab_mission);
        mMinePage = (LinearLayout) findViewById(R.id.id_tab_mine);
//        mImgIndexPage = (ImageButton) findViewById(R.id.id_tab_index_img);
//        mImgMissionPage = (ImageButton) findViewById(R.id.id_tab_mission_img);
//        mImgMinePage = (ImageButton) findViewById(R.id.id_tab_mine_img);
    }

    private void initEvents() {
        View.OnClickListener onClickListener = new View.OnClickListener() {
            public void onClick(View v) {
                //先将三个 ImageButton 置为蓝色
                resetBackgroud();
                //根据点击的 Tab 切换不同的页面及设置对应的 ImageButton 为白色
                switch (v.getId()) {
                    case R.id.id_index: selectTab(0); break;
                    case R.id.id_tab_mission: selectTab(1); break;
                    case R.id.id_tab_mine: selectTab(2); break;
                }
            }};
        //设置三个 Tab 的点击事件
        mIndexPage.setOnClickListener(onClickListener);
        mMissionPage.setOnClickListener(onClickListener);
        mMinePage.setOnClickListener(onClickListener);
    }
    private void resetBackgroud() {
        mIndexPage.setBackgroundColor(getResources().getColor(R.color.blue));
        mMissionPage.setBackgroundColor(getResources().getColor(R.color.blue));
        mMinePage.setBackgroundColor(getResources().getColor(R.color.blue));
    }
    private void selectTab(int i) {
        //根据点击的 Tab 设置对应的 tab 为白色
        switch (i) {
            case 0: mIndexPage.setBackgroundColor(getResources().getColor(R.color.blue0));break;
            case 1: mMissionPage.setBackgroundColor(getResources().getColor(R.color.blue0));break;
            case 2: mMinePage.setBackgroundColor(getResources().getColor(R.color.blue0));break;
        }
        //设置当前点击的 Tab 所对应的页面
        setCurrentFragment(i);
    }

    private void setCurrentFragment(int i)
    {
        FragmentManager fm = getSupportFragmentManager();
        FragmentTransaction trans = fm.beginTransaction();
        trans.replace(R.id.frag_layout, mFragments.get(i));
        trans.commit();
    }

    private void initFirstRun(int i)
    {
        resetBackgroud(); //重置所有 Tab
        selectTab(i); //显示第 i 个碎片
    }
}