Android開發一個簡單的互動式App

1、功能分析

• Layout定義App外觀
  • 下拉串列列出編程語言的特點
  • 點擊按鈕，開始處理
  • 文本框顯示推薦的編程語言
• 字符存盤在strings.xml
• activity定義App與用戶的互動方式
  • 根據用戶在下拉串列的選擇,在文本框中回傳編程語言
• 定制的Java程式中包含業務邏輯
  • 存盤并輸出語言與特點的對應關系

2、開發視圖布局

• 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>
  

• 預覽

  

3、按鈕事件回應

• MainActivity類

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

4、開發模型層

• ProgramExpert類，和MainActivity同級

  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類

  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封裝實體變數，final保證expert被初始化
      //final的實體變數賦值后無法改變，宣告后必須立即初始化
      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){
          //獲得Spinner參考
          Spinner spinner = findViewById(R.id.feature);
          //獲得Spinner選項
          String feature = spinner.getSelectedItem().toString();
  
          //查詢模型層
          String langunage = expert.getLangunage(feature);
  
          //獲得TextView參考
          TextView textView = findViewById(R.id.language);
          //設定TextView文字
          //textView.setText(feature);
          textView.setText(langunage);
      }
  }
  

5、測驗結果