Android学习记录（十七）

Fragment实现下拉列表

使用RadioGroup + RadioButton

1.实现步骤

1.1 新建项目【FragmentDemo】

1.2 添加所需图片素材

1.3 编写所需资源文件

1.3.1 tab_menu_channel.xml

<selector xmlns:android="http://schemas.android.com/apk/res/android">
    <item android:drawable="@mipmap/tab_channel_pressed" android:state_checked="true"/>
    <item android:drawable="@mipmap/tab_channel_normal" />

selector>

1.3.2 tab_menu_message.xml

<selector xmlns:android="http://schemas.android.com/apk/res/android">
    <item android:drawable="@mipmap/tab_message_pressed" android:state_checked="true"/>
    <item android:drawable="@mipmap/tab_message_normal" />

selector>

1.3.3 tab_menu_better.xml

<selector xmlns:android="http://schemas.android.com/apk/res/android">
    <item android:drawable="@mipmap/tab_better_pressed" android:state_checked="true"/>
    <item android:drawable="@mipmap/tab_better_normal" />

selector>

1.3.4 tab_menu_setting.xml

<selector xmlns:android="http://schemas.android.com/apk/res/android">
    <item android:drawable="@mipmap/tab_my_pressed" android:state_checked="true"/>
    <item android:drawable="@mipmap/tab_my_normal" />

selector>

1.3.5 tab_menu_text.xml

<selector xmlns:android="http://schemas.android.com/apk/res/android">
    <item android:color="@color/text_yellow" android:state_selected="true" />
    <item android:color="@color/text_gray" />
selector>

1.3.6 tab_menu_bg.xml

<selector xmlns:android="http://schemas.android.com/apk/res/android">
    <item android:state_selected="true">
        <shape>
            <solid android:color="#FFC4C4C4" />
        shape>
    item>
    <item>
        <shape>
            <solid android:color="@color/transparent" />
        shape>
    item>
selector>

1.4 activity_main.xml

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@color/bg_gray"
    tools:context=".MainActivity">


    <RelativeLayout
        android:id="@+id/ly_top_bar"
        android:layout_width="match_parent"
        android:layout_height="48dp"
        android:background="@color/bg_topbar">

        <TextView
            android:id="@+id/txt_topbar"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:layout_centerInParent="true"
            android:gravity="center"
            android:text="信息"
            android:textColor="@color/text_topbar"
            android:textSize="18sp" />

        <View
            android:layout_width="match_parent"
            android:layout_height="2px"
            android:layout_alignParentBottom="true"
            android:background="@color/div_white" />

    RelativeLayout>

    <RadioGroup
        android:id="@+id/rg_tab_bar"
        android:layout_width="match_parent"
        android:layout_height="56dp"
        android:layout_alignParentBottom="true"
        android:background="@color/bg_white"
        android:orientation="horizontal">

        <RadioButton
            android:id="@+id/rb_channel"
            style="@style/tab_menu_item"
            android:drawableTop="@drawable/tab_menu_channel"
            android:text="@string/tab_menu_alert" />

        <RadioButton
            android:id="@+id/rb_message"
            style="@style/tab_menu_item"
            android:drawableTop="@drawable/tab_menu_message"
            android:text="@string/tab_menu_profile" />

        <RadioButton
            android:id="@+id/rb_better"
            style="@style/tab_menu_item"
            android:drawableTop="@drawable/tab_menu_better"
            android:text="@string/tab_menu_pay" />

        <RadioButton
            android:id="@+id/rb_setting"
            style="@style/tab_menu_item"
            android:drawableTop="@drawable/tab_menu_setting"
            android:text="@string/tab_menu_setting"/>

    RadioGroup>

    <View
        android:id="@+id/div_tab_bar"
        android:layout_width="match_parent"
        android:layout_height="2px"
        android:layout_above="@id/rg_tab_bar"
        android:background="@color/div_white" />

    <FrameLayout
        android:id="@+id/ly_content"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_above="@id/div_tab_bar"
        android:layout_below="@id/ly_top_bar">
     FrameLayout>

RelativeLayout>

由以上代码我们可以发现，跟上一个方法比起来，我在这里使用了style.xml文件。这样做的目的是为了减少重复代码的使用，减少代码量。

<resources>

    
    <style name="AppTheme" parent="Theme.AppCompat.Light.DarkActionBar">
        
    style>

    <style name="tab_menu_item">
        "android:layout_width">0dp
        "android:layout_weight">1
        "android:layout_height">match_parent
        "android:background">@drawable/tab_menu_bg
        "android:button">@null
        "android:gravity">center
        "android:paddingTop">3dp
        "android:textColor">@drawable/tab_menu_text
        "android:textSize">18sp
    style>


resources>

1.5 AndroidManifest.xml

1.6 基于模板创建MyFragment.java

fg_content.xml

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical" android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@color/bg_white">

    <TextView
        android:id="@+id/txt_content"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:gravity="center"
        android:text="呵呵"
        android:textColor="@color/text_yellow"
        android:textSize="20sp"/>

LinearLayout>

MyFragment.java

package net.nell.fragmentdemo;

import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;

import androidx.fragment.app.Fragment;

public class MyFragment extends Fragment {
     

    private String content;
    public MyFragment(String content) {
     
        this.content = content;
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
     
        View view = inflater.inflate(R.layout.fg_content,container,false);
        TextView txt_content = (TextView) view.findViewById(R.id.txt_content);
        txt_content.setText(content);
        return view;
    }
}

1.7 MainActivity.java

package net.nell.fragmentdemo;

import android.os.Bundle;
import android.widget.RadioButton;
import android.widget.RadioGroup;

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

public class MainActivity extends AppCompatActivity implements RadioGroup.OnCheckedChangeListener{
     

    private RadioGroup rg_tab_bar;
    private RadioButton rb_channel;

    //Fragment Object
    private MyFragment fg1,fg2,fg3,fg4;
    private FragmentManager fManager;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
     
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        fManager = getSupportFragmentManager();
        rg_tab_bar = (RadioGroup) findViewById(R.id.rg_tab_bar);
        rg_tab_bar.setOnCheckedChangeListener(this);
        //获取第一个单选按钮，并设置其为选中状态
        rb_channel = (RadioButton) findViewById(R.id.rb_channel);
        rb_channel.setChecked(true);
    }


    @Override
    public void onCheckedChanged(RadioGroup group, int checkedId) {
     
        FragmentTransaction fTransaction = fManager.beginTransaction();
        hideAllFragment(fTransaction);
        switch (checkedId){
     
            case R.id.rb_channel:
                if(fg1 == null){
     
                    fg1 = new MyFragment("第一个Fragment");
                    fTransaction.add(R.id.ly_content,fg1);
                }else{
     
                    fTransaction.show(fg1);
                }
                break;
            case R.id.rb_message:
                if(fg2 == null){
     
                    fg2 = new MyFragment("第二个Fragment");
                    fTransaction.add(R.id.ly_content,fg2);
                }else{
     
                    fTransaction.show(fg2);
                }
                break;
            case R.id.rb_better:
                if(fg3 == null){
     
                    fg3 = new MyFragment("第三个Fragment");
                    fTransaction.add(R.id.ly_content,fg3);
                }else{
     
                    fTransaction.show(fg3);
                }
                break;
            case R.id.rb_setting:
                if(fg4 == null){
     
                    fg4 = new MyFragment("第四个Fragment");
                    fTransaction.add(R.id.ly_content,fg4);
                }else{
     
                    fTransaction.show(fg4);
                }
                break;
        }
        fTransaction.commit();
    }

    //隐藏所有Fragment
    private void hideAllFragment(FragmentTransaction fragmentTransaction){
     
        if(fg1 != null)fragmentTransaction.hide(fg1);
        if(fg2 != null)fragmentTransaction.hide(fg2);
        if(fg3 != null)fragmentTransaction.hide(fg3);
        if(fg4 != null)fragmentTransaction.hide(fg4);
    }

}

1.8 运行效果

仔细观察，我们会发现，今天所使用方法的样式相比较昨天的效果会更加好看。