国内大部分应用使用底部导航栏，

底部导航栏 是国内 APP 常见的导航方式， 历经： TabActivity -> ActionBar -> TabHost -> FragmentTabHost -> TabLayout 等等方式。

安卓官方文档 https://developer.android.google.cn/develop/index.html

TabLayout 是安卓辅助设计类库的一部分，设计类库的用法可以参考泡在网上的日子。

TabLayout 用法：

• 使用代码添加 Item
  TabLayout tabLayout = ...;
  tabLayout.addTab(tabLayout.newTab().setText("Tab 1"));
  tabLayout.addTab(tabLayout.newTab().setText("Tab 2"));
  tabLayout.addTab(tabLayout.newTab().setText("Tab 3"));

• 使用布局文件添加 Item
  <android.support.design.widget.TabLayout
  android:layout_height="wrap_content"
  android:layout_width="match_parent">

      <android.support.design.widget.TabItem
              android:text="@string/tab_text"/>
  
      <android.support.design.widget.TabItem
              android:icon="@drawable/ic_android"/>
  
  </android.support.design.widget.TabLayout>
  

制作底部导航栏

The bottom navigation bar on mobile

TabActivity 代码：

public class TabActivity extends AppCompatActivity {

    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_tab);
    }
    
}

activity_tab 代码：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

    <View
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_weight="1"
        android:background="@android:color/holo_blue_bright" />

    <android.support.design.widget.TabLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        app:tabBackground="@android:color/white"
        app:tabIndicatorColor="@android:color/transparent">

        <android.support.design.widget.TabItem android:layout="@layout/tab_item" />

        <android.support.design.widget.TabItem android:layout="@layout/tab_item" />

        <android.support.design.widget.TabItem android:layout="@layout/tab_item" />

        <android.support.design.widget.TabItem android:layout="@layout/tab_item" />
    </android.support.design.widget.TabLayout>
</LinearLayout>

tab_item 代码：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:gravity="center"
    android:orientation="vertical">

    <ImageView
        android:layout_width="24dp"
        android:layout_height="24dp"
        android:contentDescription="@string/app_name"
        android:scaleType="fitXY"
        android:src="@drawable/selector_tab_image" />

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/android"
        android:textColor="@color/selector_tab_text" />
</LinearLayout>

图片选择器 selector_tab_image 代码：

<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android">
    <item android:drawable="@mipmap/ic_launcher_0" android:state_selected="true" />
    <item android:drawable="@mipmap/ic_launcher_1" android:state_selected="false" />
</selector>

文字选择器 selector_tab_text 代码：

<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android">
    <item android:color="#F00" android:state_selected="true" />
    <item android:color="#0FF" android:state_selected="false" />
</selector>

使用 Java 代码添加 Item：

public class TabActivity extends AppCompatActivity {

    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_tab);

        TabLayout tabLayout = (TabLayout) findViewById(R.id.tab_layout);
        tabLayout.addTab(tabLayout.newTab().setCustomView(R.layout.tab_item));
        tabLayout.addTab(tabLayout.newTab().setCustomView(R.layout.tab_item));
        tabLayout.addTab(tabLayout.newTab().setCustomView(R.layout.tab_item));
        tabLayout.addTab(tabLayout.newTab().setCustomView(R.layout.tab_item));
    }

}

循环添加

public class TabActivity extends AppCompatActivity {

    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_tab);

        TabLayout tabLayout = (TabLayout) findViewById(R.id.tab_layout);
        String[] texts = {"安卓", "Android", "Java", "Kotlin"};
        for (String s:texts) {
            View itemView = LayoutInflater.from(this).inflate(R.layout.tab_item, tabLayout, false);
            TextView txtView = (TextView) itemView.findViewById(R.id.tv_tab_text);
            txtView.setText(s);
            tabLayout.addTab(tabLayout.newTab().setCustomView(itemView));
        }
    }

}

...

• app:tabIndicatorColor="@android:color/transparent" 隐藏 TabLayout 指示器；
• app:tabBackground="@android:color/white" 取消导航栏被点击时的阴影效果。

记录下FragmentTabHost布局：

<?xml version="1.0" encoding="utf-8"?>
<android.support.v4.app.FragmentTabHost xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@android:id/tabhost"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@color/color_f8f8f8">

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical">

        <FrameLayout
            android:id="@android:id/tabcontent"
            android:layout_width="match_parent"
            android:layout_height="0dp"
            android:layout_weight="1" />

        <TabWidget
            android:id="@android:id/tabs"
            android:layout_width="match_parent"
            android:layout_height="49dp"
            android:layout_marginTop="1dp"
            android:background="@android:color/white" />
    </LinearLayout>
</android.support.v4.app.FragmentTabHost>