[移动开发]Android开发一个简单的交互式App

1、功能分析

• Layout定义App外观
  • 下拉列表列出编程语言的特点
  • 点击按钮，开始处理
  • 文本框显示推荐的编程语言
• 字符存储在strings.xml
• activity定义App与用户的交互方式
  • 根据用户在下拉列表的选择,在文本框中返回编程语言
• 定制的Java程序中包含业务逻辑
  • 存储并输出语言与特点的对应关系

2、开发视图布局

• activity_main.xml

  <?xml version="1.0" encoding="utf-8"?>
  <androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
      xmlns:app="http://schemas.android.com/apk/res-auto"
      xmlns:tools="http://schemas.android.com/tools"
      android:layout_width="match_parent"
      android:layout_height="match_parent"
      tools:context=".MainActivity">
  
      <LinearLayout
          android:layout_width="match_parent"
          android:layout_height="match_parent"
          android:orientation="vertical"
          tools:layout_editor_absoluteX="186dp"
          tools:layout_editor_absoluteY="366dp">
  
          <Spinner
              android:id="@+id/feature"
              android:layout_width="match_parent"
              android:layout_height="wrap_content"
              android:entries="@array/feature"
              android:minHeight="32dp" />
  
          <Button
              android:id="@+id/find_language"
              android:layout_width="match_parent"
              android:layout_height="wrap_content"
              android:onClick="onClickButton"
              android:text="@string/find_language" />
  
          <TextView
              android:id="@+id/language"
              android:layout_width="match_parent"
              android:layout_height="wrap_content"
              android:text="@string/language" />
  
      </LinearLayout>
  </androidx.constraintlayout.widget.ConstraintLayout>
  

• strings.xml

  <resources>
      <string name="app_name">ProgramAdviser</string>
      <string name="find_language">Find Language</string>
      <string name="language">Select and Click</string>
      <string-array name="feature">
          <item>fast</item>
          <item>easy</item>
          <item>new</item>
          <item>OO</item>
      </string-array>
  </resources>
  

• 预览

  

3、按钮事件响应

• MainActivity类

  public class MainActivity extends AppCompatActivity {
      @Override
      protected void onCreate(Bundle savedInstanceState) {
          super.onCreate(savedInstanceState);
          setContentView(R.layout.activity_main);
      }
  
      public void onClickButton(View button){
          //获得Spinner引用
          Spinner spinner = findViewById(R.id.feature);
          //获得Spinner选项
          String feature = spinner.getSelectedItem().toString();
          //获得TextView引用
          TextView textView = findViewById(R.id.language);
          //设置TextView文字
          textView.setText(feature);
      }
  }
  

4、开发模型层

• ProgramExpert类，和MainActivity同级

  public class ProgramExpert {
      public String getLangunage(String feature){
          String result;
          switch (feature){
              case "fast":
                  result = "C/C++";
                  break;
              case "easy":
                  result = "Python";
                  break;
              case "new":
                  result = "Kotlin";
                  break;
              case "OO" :
                  result = "Java";
                  break;
              default:
                  result = "You got me";
          }
          return result;
      }
  }
  

• 修改MainActivity类

  package szst.it.ping.programadviser;
  
  import androidx.appcompat.app.AppCompatActivity;
  
  import android.os.Bundle;
  import android.view.View;
  import android.widget.Spinner;
  import android.widget.TextView;
  
  public class MainActivity extends AppCompatActivity {
  
      //private封装实例变量，final保证expert被初始化
      //final的实例变量赋值后无法改变，声明后必须立即初始化
      private final ProgramExpert expert = new ProgramExpert();
  
      @Override
      protected void onCreate(Bundle savedInstanceState) {
          super.onCreate(savedInstanceState);
          setContentView(R.layout.activity_main);
      }
  
      public void onClickButton(View button){
          //获得Spinner引用
          Spinner spinner = findViewById(R.id.feature);
          //获得Spinner选项
          String feature = spinner.getSelectedItem().toString();
  
          //查询模型层
          String langunage = expert.getLangunage(feature);
  
          //获得TextView引用
          TextView textView = findViewById(R.id.language);
          //设置TextView文字
          //textView.setText(feature);
          textView.setText(langunage);
      }
  }
  

5、测试结果