別のインテントから配列リストにアイテムを追加する

Question

BookオブジェクトのListViewを持つアプリがあります。私は、別のブックを追加してMainActivityに情報を戻すことができる別のアクティビティ（AddBook）に移動するボタンをクリックします。元のBookオブジェクトを作成してListViewに追加することはできますが、MainActivityに戻るときにAddボタン（MainActivity上）をクリックしてAddBookを再度実行して2番目のブックを追加しようとすると、 2番目のエントリによって。私はループや条件付きが必要だと思うが、私はそれを理解することはできない。

私はAddBook活動

package com.the93rd.android.bookcatalog; 

    import android.content.Intent; 
    import android.os.Bundle; 
    import android.support.v7.app.AppCompatActivity; 
    import android.view.View; 
    import android.widget.AdapterView; 
    import android.widget.Button; 
    import android.widget.ListView; 
    import android.widget.Toast; 

    import java.util.ArrayList; 

    public class MainActivity extends AppCompatActivity { 

Button mAddBook; 
public ArrayList<Book> books; 
public ListView listView; 
public BookListViewAdapter bookAdapter; 

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

    //Array List of Book objects 
    books = new ArrayList<>(); 

    books.add(new Book("J.K. Rolling", "Harry Potter and The Sorcerers Stone", 8, 
      "0439708184", "Yes")); 
    books.add(new Book("Eoin Colfer", "The Artic Accident", 5, 
      "1423124529", "Yes")); 
    books.add(new Book("George S. Clason", "The Richest Man in Babylon", 9, 
      "1505339111", "No")); 
    books.add(new Book("Khaled Hosseini", "The Kite Runner", 10, 
      "159463193X", "Yes")); 
    books.add(new Book("Daniel Keyes", "Flowers For Algernon", 8, 
      "0156030306", "No")); 

    listView = (ListView) findViewById(R.id.list); 
    bookAdapter = new BookListViewAdapter(this, books); 

    listView.setAdapter(bookAdapter); 


    //Open BookDetails Activity to Display more book information 
    listView.setOnItemClickListener(new AdapterView.OnItemClickListener() { 
     @Override 
     public void onItemClick(AdapterView<?> parent, View view, int position, long id) { 

      //Get ArrayList element 
      Book book = books.get(position); 

      //Get fields for current Book element 
      String passAuthor = book.getAuthor(); 
      String passTitle = book.getTitle(); 
      int passRating = book.getRating(); 
      String passIsbn = book.getIsbn(); 
      String passSeries = book.getSeries(); 

      Toast.makeText(MainActivity.this, book.getAuthor(), Toast.LENGTH_SHORT).show(); 

      //Pass Extras for Book element to BookDetails Activity 
      Intent openDetail = new Intent(MainActivity.this, BookDetails.class); 
      openDetail.putExtra("Author", passAuthor); 
      openDetail.putExtra("Title", passTitle); 
      openDetail.putExtra("Rating", passRating); 
      openDetail.putExtra("Isbn", passIsbn); 
      openDetail.putExtra("Series", passSeries); 
      startActivity(openDetail); 
     } 
    }); 

    //Open AddBook Activity 
    mAddBook = (Button) findViewById(R.id.add_book); 
    mAddBook.setOnClickListener(new View.OnClickListener() { 
     @Override 
     public void onClick(View v) { 

      Intent addBook = new Intent(MainActivity.this, AddBook.class); 
      startActivity(addBook); 
     } 
    }); 

    //Get extras from AddBook Activity 
    Intent intent = getIntent(); 

    String addAuthor = intent.getStringExtra("addAuthor"); 
    String addTitle = intent.getStringExtra("addTitle"); 
    String addRating = intent.getStringExtra("addRating"); 
    String addIsbn = intent.getStringExtra("addIsbn"); 
    String addSeries = intent.getStringExtra("addSeries"); 

    if(addAuthor != null){ 

     //Add variables from AddBook activity to new Book object 
     books.add(new Book(addAuthor, addTitle, 5, addIsbn, addSeries)); 
     bookAdapter.notifyDataSetChanged(); 
    } 

} 

}

Answer 1

あなたはそうではなく、startActivityよりstartActivityForResultを使用することができます上のフィールドに入力する前に、オブジェクトが自動的に追加されますので、私はライン94上のif文を追加しましたあなたは、あなたのadBookActivity例

package com.the93rd.android.bookcatalog; 

    import android.content.Intent; 
    import android.os.Bundle; 
    import android.support.v7.app.AppCompatActivity; 
    import android.view.View; 
    import android.widget.AdapterView; 
    import android.widget.Button; 
    import android.widget.ListView; 
    import android.widget.Toast; 

    import java.util.ArrayList; 

    public class MainActivity extends AppCompatActivity { 
    Button mAddBook; 
    public ArrayList<Book> books; 
    public ListView listView; 
    public BookListViewAdapter bookAdapter; 

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

     //Array List of Book objects 
     books = new ArrayList<>(); 

     books.add(new Book("J.K. Rolling", "Harry Potter and The Sorcerers Stone", 8, 
       "0439708184", "Yes")); 
     books.add(new Book("Eoin Colfer", "The Artic Accident", 5, 
       "1423124529", "Yes")); 
     books.add(new Book("George S. Clason", "The Richest Man in Babylon", 9, 
       "1505339111", "No")); 
     books.add(new Book("Khaled Hosseini", "The Kite Runner", 10, 
       "159463193X", "Yes")); 
     books.add(new Book("Daniel Keyes", "Flowers For Algernon", 8, 
       "0156030306", "No")); 

     listView = (ListView) findViewById(R.id.list); 
     bookAdapter = new BookListViewAdapter(this, books); 

     listView.setAdapter(bookAdapter); 


     //Open BookDetails Activity to Display more book information 
     listView.setOnItemClickListener(new AdapterView.OnItemClickListener() { 
      @Override 
      public void onItemClick(AdapterView<?> parent, View view, int position, long id) { 

       //Get ArrayList element 
       Book book = books.get(position); 

       //Get fields for current Book element 
       String passAuthor = book.getAuthor(); 
       String passTitle = book.getTitle(); 
       int passRating = book.getRating(); 
       String passIsbn = book.getIsbn(); 
       String passSeries = book.getSeries(); 

       Toast.makeText(MainActivity.this, book.getAuthor(), Toast.LENGTH_SHORT).show(); 

       //Pass Extras for Book element to BookDetails Activity 
       Intent openDetail = new Intent(MainActivity.this, BookDetails.class); 
       openDetail.putExtra("Author", passAuthor); 
       openDetail.putExtra("Title", passTitle); 
       openDetail.putExtra("Rating", passRating); 
       openDetail.putExtra("Isbn", passIsbn); 
       openDetail.putExtra("Series", passSeries); 
       startActivity(openDetail); 
      } 
     }); 

     //Open AddBook Activity 
     mAddBook = (Button) findViewById(R.id.add_book); 
     mAddBook.setOnClickListener(new View.OnClickListener() { 
      @Override 
      public void onClick(View v) { 

       Intent addBook = new Intent(MainActivity.this, AddBook.class); 
       int requestCode = 1; 
       startActivityForResult(addBook, requestCode); 
      } 
     }); 

    } 

    @Override 
    protected void onActivityResult(int requestCode, int resultCode, Intent data) { 
     super.onActivityResult(requestCode, resultCode, data); 

     String addAuthor = data.getStringExtra("addAuthor"); 
     String addTitle = data.getStringExtra("addTitle"); 
     String addRating = data.getStringExtra("addRating"); 
     String addIsbn = data.getStringExtra("addIsbn"); 
     String addSeries = data.getStringExtra("addSeries"); 

     if(addAuthor != null){ 
      //Add variables from AddBook activity to new Book object 
      books.add(new Book(addAuthor, addTitle, 5, addIsbn, addSeries)); 
      bookAdapter.notifyDataSetChanged(); 
     } 

    } 
} 

ため、AdBook活動からのデータを受信setResult(1, data)を呼び出して確認することができますアクティビティを閉じる前に

*定数として変更1（requestcode）、コードを読みやすくするために

Answer 2

私はあなたがsqliteのDBを使用する必要があります最善の方法だと思います。リストボックスの項目をsqlite db tableから設定すると、あなたのアプリが速く実行されます。