前言

问题1：fragment干什么用的？

Fragment是Android3.0后引入的一个新的API，他出现的初衷是为了适应大屏幕的平板电脑
而使用Fragment 我们可以把屏幕划分成几块，然后进行分组，进行一个模块化的管理！从而可以更加方便的在运行过程中动态地更新Activity的用户界面
现在很多页面底部导航栏用到fragment

问题2：Fragment & v4.app.Fragment?为什么有两个？

Android 3.0(api11)之后引入的fragment，之前的无法兼容，产生了v4.app.Fragment.*

使用区别：

如果你使用了v4包下的Fragment,那么所在的那个Activity就要继承FragmentActivity
getFragmentManager( )改成getSupportFragmentManager( )

生命周期

image.png

无标题.png

Android.app.fragment

one.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
    xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent"
    android:layout_height="match_parent">
    <fragment
        android:layout_width="match_parent"
        android:id="@+id/fragment"
        android:name="com.example.rtyui.androidteach.FragmentApp"
        android:layout_height="match_parent"/>
</RelativeLayout>

fragment_three.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:text="fragment_three"
        android:gravity="center"/>
</LinearLayout>

class FragmentApp

public class FragmentApp extends Fragment {

    private View root;
    @Nullable
    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        root = inflater.inflate(R.layout.fragment_three, container, false);
        return root;
    }
}

android.support.v4.app.Fragment

xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
    xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent"
    android:layout_height="match_parent">
    <RelativeLayout
        android:layout_width="match_parent"
        android:id="@+id/fragment"
        android:layout_height="match_parent"/>
</RelativeLayout>

Activity

public class One extends FragmentActivity {

    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.one);
        Fragment fragment = new FragmentThree();
        getSupportFragmentManager().beginTransaction().replace(R.id.fragment, fragment).commit();
    }
}

实战（底部导航栏）

activity 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"
    android:orientation="vertical">
    <Button
        android:layout_width="match_parent"
        android:layout_height="50dp"
        android:id="@+id/btn"
        android:text="跳转"/>
    <RelativeLayout
        android:layout_width="match_parent"
        android:layout_height="0px"
        android:id="@+id/top"
        android:layout_weight="1"/>
    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="60dp"
        android:orientation="horizontal">
        <LinearLayout
            android:layout_width="0px"
            android:layout_weight="1"
            android:id="@+id/btn_one"
            android:orientation="vertical"
            android:layout_height="match_parent">
            <ImageView
                android:layout_width="match_parent"
                android:src="@mipmap/ic_launcher"
                android:padding="5dp"
                android:layout_height="40dp" />
            <TextView
                android:layout_width="match_parent"
                android:text="底部1"
                android:gravity="center"
                android:layout_height="20dp" />
        </LinearLayout>
        <LinearLayout
            android:layout_width="0px"
            android:layout_weight="1"
            android:orientation="vertical"
            android:id="@+id/btn_two"
            android:layout_height="match_parent">
            <ImageView
                android:layout_width="match_parent"
                android:src="@mipmap/ic_launcher"
                android:padding="5dp"
                android:layout_height="40dp" />
            <TextView
                android:layout_width="match_parent"
                android:text="底部2"
                android:gravity="center"
                android:layout_height="20dp" />
        </LinearLayout>
        <LinearLayout
            android:layout_width="0px"
            android:layout_weight="1"
            android:id="@+id/btn_three"
            android:orientation="vertical"
            android:layout_height="match_parent">
            <ImageView
                android:layout_width="match_parent"
                android:src="@mipmap/ic_launcher"
                android:padding="5dp"
                android:layout_height="40dp" />
            <TextView
                android:layout_width="match_parent"
                android:text="底部3"
                android:gravity="center"
                android:layout_height="20dp" />
        </LinearLayout>
    </LinearLayout>
</LinearLayout>

结构，代码都是类似的

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activity class

package com.example.rtyui.androidteach;

import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentActivity;
import android.view.View;

public class Main extends FragmentActivity {

    private Fragment fragmentOne = null;
    private Fragment fragmentTwo = null;
    private Fragment fragmentThree = null;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        fragmentOne = new FragmentOne();
        fragmentTwo = new FragmentTwo();
        fragmentThree = new FragmentThree();
        getSupportFragmentManager().beginTransaction()
                .add(R.id.top, fragmentOne)
                .add(R.id.top, fragmentTwo)
                .add(R.id.top, fragmentThree).commit();
        showFrag(1);

        findViewById(R.id.btn_one).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                showFrag(1);
            }
        });
        findViewById(R.id.btn_two).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                showFrag(2);
            }
        });
        findViewById(R.id.btn_three).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                showFrag(3);
            }
        });
    }

    private void showFrag(int sign){
        switch (sign){
            case 1:
                getSupportFragmentManager().beginTransaction().hide(fragmentTwo).hide(fragmentThree).show(fragmentOne).commit();
                break;
            case 2:
                getSupportFragmentManager().beginTransaction().hide(fragmentOne).hide(fragmentThree).show(fragmentTwo).commit();
                break;
            case 3:
                getSupportFragmentManager().beginTransaction().hide(fragmentOne).hide(fragmentTwo).show(fragmentThree).commit();
                break;
        }
    }
}