java - 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。用户输入标题，应用程序会在 Google 图书中搜索该标题。
我最初只有一项 Activity 和布局。我决定使用两种布局(一种用于用户输入标题，另一种显示结果)；必须创建另一个 Activity ，因为结果布局抛出有关“null”对象引用的异常。
创建第二个 Activity 后，我使用 Intent 在两个 Activity 之间传输列表数据；我很快就发现我必须使用Serialize或Parcelable对象来达到目的。
按照 Pass list of objects from one activity to other activity in android 的说明进行操作& https://www.vogella.com/tutorials/AndroidParcelable/article.html ，我都未能实现这两者，因为 Serialize 发送了一个空的 ArrayList(因此，一个空的结果页面，即使有图书命中) 和 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.html 实现 API并且也不能使用 Fragment。更好的结构是使用单个 Activity ，View.GONE 我非常珍惜的背景图像，并在搜索字段下显示图书对象列表。但对于 future 的项目来说，对 Serialize & Parcelable 进行后续处理是件好事。 那么各位开发者，有什么解决办法吗？

FirstActivity screenshot SecondActivity screeenshot

这是我的代码: 主要 Activity :

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();
    }

}

第二个 Activity :

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);
        }

    }
}

图书对象:

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

您可以声明一个变量来处理您的 data = new ArrayList<Book>();如public static ..但是不建议将其用于高级代码库，但对于您的结构，您可以实现它。

只需声明一个像上面这样的变量 protected void onCreate()在 FirstActivity ..

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

并转移data来自public void onLoadFinished (Loader<List<Book>> loader, List<Book> data)至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，您也可以尝试调试它 Log.d(TAG, String.valueOf(data.size()));

和第二个 Activity

@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

    ....
    ....
}