如何在两个活动之间传递类对象？答案

【问题标题】：How I can pass class object between two activities?如何在两个活动之间传递类对象？
【发布时间】：2016-06-03 13:25:44
【问题描述】：

我有一个 Books.java 类 implements Book.java 的列表，在 MainActivity.java 中我用书籍填充对象库。我想将对象库从MainActivity.java 发送到ListActivity.java 但不适用于i.putExtra. 我该怎么做？

书籍.java

import java.util.ArrayList;
import java.util.List;


public class Books implements DataAggregate <Book>{
private List<Book> books;

public Books(){};

public List<Book> getAll() {
    return this.getBooks();
}

public int size() {
    return this.getBooks().size();
}

public void insert(Book element) {
    this.getBooks().add(element);
}

public void delete(Book element) {
    this.getBooks().remove(element);
}

private List<Book> getBooks() {
    if (books==null){
        books=new ArrayList<Book>();
    }
    return books;
}

}

MainActivity.java

Books library;
for (int i = 0; i<db_books.size(); i++){
       String name = db_books.get(i).getBookName();
       String author = db_books.get(i).getBookAuthor();
       String epc = db_books.get(i).getBookEpc();
       Integer number = db_books.get(i).getNumBooks();
       Book myBook = new Book(name, author, epc, number);
       library.insert(myBook);
}
Intent i = new Intent(getApplicationContext(),ListActivity.class);
i.putExtra("library",library);
startActivity(i);

ListActivity.java

Books library = extras.getString("library");

Book.java

public class Book implements Serializable {

    private String bookName;
    private String bookAuthor;
    private String bookEpc;
    private Integer numBooks;


    public Book(){

    }

    public Book(String bname, String bauthor, String bepc, Integer nbooks){
        this.bookName = bname;
        this.bookAuthor = bauthor;
        this.bookEpc = bepc;
        this.numBooks = nbooks;
    }

    public String getBookName() {
        return bookName;
    }

    public void setBookName(String bookName) {
        this.bookName = bookName;
    }

    public String getBookAuthor() {
        return bookAuthor;
    }

    public void setBookAuthor(String bookAuthor) {
        this.bookAuthor = bookAuthor;
    }

    public String getBookEpc() {
        return bookEpc;
    }

    public void setBookEpc(String bookEpc) {
        this.bookEpc = bookEpc;
    }

    public Integer getNumBooks() {
        return numBooks;
    }

    public void setNumBooks(Integer numBooks) {
        this.numBooks = numBooks;
    }

    public void prettyPrint(){

        Log.d("Book:", this.bookName+" "+this.bookAuthor+" "+this.bookEpc+" "+this.numBooks.toString());
    }
}

【问题讨论】：

请参阅此link。希望对你有帮助。
@Lawrance 我必须将 Books.java 实现为可序列化？
@Lawrance 不起作用，java.lang.RuntimeException: Unable to start activity ComponentInfo{upf.mybooks/upf.mybooks.ListActivity}: java.lang.ClassCastException: upf.mybooks.model.Books cannot be cast to java.util.List

标签： java android android-layout android-intent android-inflate

【解决方案1】：

代替

Books library = extras.getString("library");

你应该这样做

Books library = (Books) extras. getSerializableExtra("library");

【讨论】：

那不行，FATAL EXCEPTION: main Process: upf.mybooks, PID: 30008 java.lang.ClassCastException: upf.mybooks.model.Books cannot be cast to java.io.Serializable

【解决方案2】：

我是这样解决的：

要在两个活动之间传递，我使用这个，

在 MainActivity.java 中：

Intent intent=new Intent(getApplicationContext(),ListActivity.class);
Bundle bundle=new Bundle();
bundle.putSerializable("library", library);
intent.putExtras(bundle);
startActivity(intent);

在 ListActivity.java 中获取库：

Intent intent=this.getIntent();
Bundle bundle=intent.getExtras();
final Books library =(Books)bundle.getSerializable("library");

ListActivity.java 中的最终库对象包含所有书籍。

【讨论】：

【解决方案3】：

试试这个可能对你有帮助

像这样发送

 Intent i = new Intent(getApplicationContext(),DetailedBookActivity.class);
 i.putExtra("library",library);

然后变成这样

Book libs= new Book();
libs = (Book)getIntent().getSerializableExtra("library");

【讨论】：

这不行，i.putExtra("library", (Serializable) library);
它给出了一个错误FATAL EXCEPTION: main Process: upf.mybooks, PID: 27029 java.lang.ClassCastException: upf.mybooks.model.Books cannot be cast to java.io.Serializable

【解决方案4】：

Books 类必须实现 Serializable

import java.util.ArrayList;
import java.util.List;


public class Books implements DataAggregate <Book>, Serializable {
    private List<Book> books;

    public Books(){};

    public List<Book> getAll() {
    return this.getBooks();
    }

    public int size() {
        return this.getBooks().size();
    }

    public void insert(Book element) {
        this.getBooks().add(element);
    }

    public void delete(Book element) {
        this.getBooks().remove(element);
    }

    private List<Book> getBooks() {
        if (books==null){
            books=new ArrayList<Book>();
        }
        return books;
    }
}

主活动

Books library;
for (int i = 0; i<db_books.size(); i++){
   String name = db_books.get(i).getBookName();
   String author = db_books.get(i).getBookAuthor();
   String epc = db_books.get(i).getBookEpc();
   Integer number = db_books.get(i).getNumBooks();
   Book myBook = new Book(name, author, epc, number);
   library.insert(myBook);
}
// don't use applicationContext. use activity context "this".
Intent i = new Intent(this, ListActivity.class);
i.putExtra("library", library);
startActivity(i);

和 ListActivity 获取意图

Books library = (Books) getIntent().getSerializableExtra("library");

【讨论】：

【解决方案5】：

在我看来，首先你应该使用 Parcelable。有关详细信息，请参阅以下链接。

Link1

Link2

【讨论】：

【解决方案6】：

first your Books class implements to Serializable.


 Intent i = new Intent(getApplicationContext(),ListActivity.class);
 i.putExtra("library",library);
startActivity(i);

get method 

Intent i = getIntent();
Book libs= new Book();
libs = (Book) i.getSerializableExtra("library");

【讨论】：