如何使用 Android 中 FirstActivity 的数据填充 SecondActivity 上的 ListView？

Question

我正在开发一个图书搜索应用程序项目。 用户输入一个标题，应用程序会在 Google 图书中搜索它。
我最初有一个活动和布局。 我决定使用两种布局（一种供用户输入标题，另一种显示结果）； 必须创建另一个活动，因为结果布局引发了关于“空”object 参考的异常。
创建第二个活动后，我使用意图在两个活动之间传输列表数据； 我很快就发现我必须为此目的使用Serialize或Parcelable object。
Following instructions at Pass list of objects from one activity to other activity in android & https://www.vogella.com/tutorials/AndroidParcelable/article.html , I failed at implementing both, because Serialize sent an empty ArrayList (thus, an空结果页面，即使有书籍点击）并且Parcelable 每次我使用它时都会抛出不同的异常，可能是因为我使用 ArrayAdapter 用书籍填充 ListView。
我认为我还没有准备好在https://www.vogella.com/tutorials/AutoValue/article.htmlments上实现 API。 更好的结构是使用单个活动， View.GONE我非常珍惜的背景图像，并在搜索字段下显示书籍对象列表。 但是最好对 Serialize & Parcelable 进行跟进——以用于未来的项目。 那么，各位开发者，有什么办法解决这个问题呢？

第一活动截图第二活动截图

这是我的代码： MainActivity：

package project.android.gbookslisting;

import android.app.LoaderManager;
import android.content.Intent;
import android.content.Loader;
import android.graphics.Color;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;

import java.io.Serializable;
import java.util.ArrayList;
import java.util.List;

import androidx.appcompat.app.AppCompatActivity;

import static project.android.gbookslisting.ResultsActivity.adapter;

//import android.support.v4.content.AsyncTaskLoader;
//import android.support.v7.app.AppCompatActivity;

public class ParamsActivity extends AppCompatActivity implements LoaderManager.LoaderCallbacks<List<Book>>, Serializable {

    private static final int LOADER_ID = 0;
    private static String LOG_TAG = ParamsActivity.class.getName();
    EditText text;
    String query;
    private LoaderManager loaderManager = getLoaderManager();

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


        Button query = findViewById(R.id.search_button);
        text = findViewById(R.id.deets_field);


        query.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick (View view) {
                if (text.getText().toString().length() > 0) {                    loaderManager.initLoader(LOADER_ID, null, ParamsActivity.this);
                } else if (text.getText().length() < 1) {
                    text.setHint("Please enter book title/details");
                    text.setHintTextColor(Color.RED);
                }
            }
        });

    }

    @Override
    public Loader<List<Book>> onCreateLoader (int i, Bundle bundle) {
        query = text.getText().toString();
        return new BookLoader(this, query);
    }

    @Override
    public void onLoadFinished (Loader<List<Book>> loader, List<Book> data) {
        // If there is a valid list of {@link Book}s, then add them to the adapter's dataset. This will trigger the ListView to update.
        if (data != null && !data.isEmpty()) {

            data = new ArrayList<Book>();

            Intent i = new Intent(getApplicationContext(), ResultsActivity.class);
            i.putExtra("data", (Serializable) data);
            startActivity(i);
        }
    }

    @Override
    public void onLoaderReset (Loader loader) {
        adapter = new Adapt(this, new ArrayList<Book>());
        adapter.clear();
    }

}

第二活动：

package project.android.gbookslisting;

import android.content.Intent;
import android.net.Uri;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ListView;
import android.widget.TextView;

import java.io.Serializable;
import java.util.ArrayList;

import androidx.appcompat.app.AppCompatActivity;

public class ResultsActivity extends AppCompatActivity implements Serializable {

    static Adapt adapter;
    static TextView emptyResult;
    ListView bookEntries;
    String LOG_TAG = ResultsActivity.class.getName();

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

        Intent i = getIntent();
        ArrayList<Book> books = (ArrayList<Book>) i.getSerializableExtra("data");

        emptyResult = findViewById(R.id.matches_nill);
        emptyResult.setText(R.string.matches0);

        if (!books.isEmpty()) {
            emptyResult.setVisibility(View.GONE);

            // Create a new adapter that takes a rich (or otherwise empty) list of books as input
            adapter = new Adapt(this, new ArrayList<Book>());

            // Get the list of books from {@link Search}
            bookEntries = findViewById(R.id.catalog);           

            bookEntries.setAdapter(adapter);
            bookEntries.setEmptyView(emptyResult);

            bookEntries.setOnItemClickListener(new AdapterView.OnItemClickListener() {
                @Override
                public void onItemClick (AdapterView<?> adapterView, View view, int position, long l) {
                    // Find the current book that was clicked on
                    Book currentBook = adapter.getItem(position);

                    // Convert the String URL into a URI object (to pass into the Intent constructor)
                    Uri bookUri = Uri.parse(currentBook.getPage());

                    // Create a new intent to view the book URI
                    Intent websiteIntent = new Intent(Intent.ACTION_VIEW, bookUri);

                    // Send the intent to launch a new activity
                    startActivity(websiteIntent);
                }
            });

//            adapter.clear();

            adapter.addAll(books);
        } else {
            emptyResult.setVisibility(View.VISIBLE);
            emptyResult.setText(R.string.matches0);
        }

    }
}

书籍对象：

package project.android.gbookslisting;

import java.io.Serializable;
import java.util.Date;

public class Book {

    private String book_title;
    private String author;
    private String publishing_year;
    private String page;


    public Book (String theTitle, String theAuthor, String theYear, String thePage) {
        this.book_title = theTitle;
        this.author = theAuthor;
        this.publishing_year = theYear;
        this.page = thePage;
    }


    public Book setBook_title (String book_title) {
        this.book_title = book_title;
        return this;
    }

    public Book setAuthor (String author) {
        this.author = author;
        return this;
    }

    public Book setPublishing_year (String publishing_year) {
        this.publishing_year = publishing_year;
        return this;
    }

    public Book setPage (String page) {
        this.page = page;
        return this;
    }

    protected String getAuthor () {
        return author;
    }

    protected String getPublishing_year () { return publishing_year; }

    protected String getPage () {
        return page;
    }

    protected String getBook_title () {
        return book_title;
    }
}

Answer 1

您可以声明将处理您的data = new ArrayList<Book>(); 作为public static .. 但是不建议用于高级代码库，但对于您的结构，您可以实现它。

只需在FirstActivity中声明一个像上面protected void onCreate()这样的变量 ..

public static List<Book> book_data = new ArrayList<>();

并将data从public void onLoadFinished (Loader<List<Book>> loader, List<Book> data)到book_data

@Override
public void onLoadFinished (Loader<List<Book>> loader, List<Book> data) {
    // If there is a valid list of {@link Book}s, then add them to the adapter's dataset. This will trigger the ListView to update.
    if (data != null && !data.isEmpty()) {

        //data = new ArrayList<Book>();
        book_data = data;

        Intent i = new Intent(getApplicationContext(), ResultsActivity.class);
        startActivity(i);
    }
}`

如果它包含值Log.d(TAG, String.valueOf(data.size()));也可以尝试调试它

并在SecondActivity

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

    List<Book> books = new ArrayList<>();
    books = FirstActivity.book_data; //Get the data from the First Activity

    ....
    ....
}

Answer 2

好的，所以我能够更正Parcelable接口的实现，现在FirstActivity将数据传递给SecondActivity 。 就是这个：

package project.android.gbookslisting;

import android.os.Parcel;
import android.os.Parcelable;

public class Book implements Parcelable {

    private String book_title;
    private String author;
    private String publishing_year;
    private String page;


    public Book (String theTitle, String theAuthor, String theYear, String thePage) {
        this.book_title = theTitle;
        this.author = theAuthor;
        this.publishing_year = theYear;
        this.page = thePage;
    }

    public Book(Parcel in) {
        this.book_title = in.readString();
        this.author = in.readString();
        this.publishing_year = in.readString();
        this.page = in.readString();
    }

    public static final Creator<Book> CREATOR = new Creator<Book>() {
        @Override
        public Book createFromParcel (Parcel in) {
            return new Book(in);
        }

        @Override
        public Book[] newArray (int size) {
            return new Book[size];
        }
    };

    protected String getAuthor () { return author; }

    protected String getPublishing_year () { return publishing_year; }

    protected String getPage () {
        return page;
    }

    protected String getBook_title () {
        return book_title;
    }

    @Override
    public int describeContents () {
        return 0;
    }

    @Override
    public void writeToParcel (Parcel parcel, int flags) {
        parcel.writeString(book_title);
        parcel.writeString(author);
        parcel.writeString(publishing_year);
        parcel.writeString(page);
    }

}

我在 GitHub @ GBooks Listing上共享了存储库，等待更多功能/更新。

ResultsActivity当然看起来很蹩脚，但我会改进主题和任何影响外观的东西。 谢谢。