当使用另一个对象构造自定义对象时，有没有办法使它可打包？

Question

我正在编写一个与汽车 classifieds API 接口的应用程序。我想要两个 windows：一个是用户输入他们想要的汽车类型，另一个是显示结果。

我的 API return 是一个很大的 JSON 文件，每辆车大约有 40 个参数，我对其中只有大约 20 个感兴趣。我有一个自定义 class 来存储 return 由 API 编辑的一些数据。在这个 class（称为 CarListing）的构造函数中，我传递了一个 JSON 对象并在构造函数中进行 JSON 解析。

此 class 然后在线程 HttpGet activity 内部调用，它本身由 MainActivity 调用。因此，对于给定的搜索，我希望从 API 中获得不止一个结果。我能够成功地将自定义对象 return 发送到 MainActivity，但是我在将此数据从 MainActivity 发送到 SecondActivity 时遇到了问题。最后，我想将 HashMap 传递给适配器，以便我可以在我制作的自定义布局中使用它。

我在 Internet 上看到的大多数响应都涉及使用 Parcelable，但我不认为 JSONObject（也不是 HashMap）是 Parcelable 对象。我已经尝试在 CarListing class 中实现它，但是 Android Studio 不喜欢我将 JSONObject 作为构造函数对象传递。

那么使我的自定义对象可打包的最佳方法是什么？我应该在构造函数之外（即在我的 HttpGet 线程中）进行 JSON 解析，然后将所有 20-25 个值作为参数传递吗？我认为我最大的问题是构造函数，但我可能是不正确的。感谢任何帮助，如有必要，我可以提供更多信息。

这是我的自定义对象 CarListing 的代码：

package com.example.carsearchapp;

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

import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;

import java.io.IOException;
import java.io.Serializable;
import java.text.NumberFormat;
import java.util.ArrayList;
import java.util.HashMap;

public class CarListing
{
    /* vehicle parameters */
    String make, model, trim, vin, color, condition, transmission, engine, drivetype, seller_type, seller_name, website, city, state;
    int year, price, mileage, cylinders;
    double distance;
    ArrayList<String> images;

    /* carfax parameters */
    boolean one_owner, clean_title;

    /* local variables that may be important */
    int index;
    JSONObject img_json, build, dealer;
    JSONArray img_array;

    public HashMap<String, String> listview_hashmap;

    /* Most strings are default N/A. Most integers are default 1, or 1970 for the case of years. */
    public CarListing(JSONObject input, int index)
    {
        try
        {
            this.images = new ArrayList<>();
            this.index = index;
            this.listview_hashmap = new HashMap<>();

            if(input.has("vin")) this.vin = input.getString("vin");
            else this.vin = "N/A";

            if(input.has("price")) this.price = input.getInt("price");
            else this.price = 1;

            if(input.has("mileage")) this.mileage = input.getInt("mileage");
            else this.mileage = 1;

            if(input.has("vdp_url")) this.website = input.getString("vdp_url");
            else this.website = "N/A";

            if(input.has("carfax_1_owner")) this.one_owner = input.getBoolean("carfax_1_owner");
            else this.one_owner = true;

            if(input.has("carfax_clean_title")) this.clean_title = input.getBoolean("carfax_clean_title");
            else this.clean_title = true;

            if(input.has("exterior_color")) this.color = input.getString("exterior_color");
            else this.color = "N/A";

            if(input.has("seller_type")) this.seller_type = input.getString("seller_type");
            else this.seller_type = "N/A";

            if(input.has("inventory_type")) this.condition = input.getString("inventory_type");
            else this.condition = "N/A";

            if(input.has("build"))
            {
                this.build = input.getJSONObject("build");

                if(this.build.has("year")) this.year = this.build.getInt("year");
                else this.year = 1970;

                if(this.build.has("make")) this.make = this.build.getString("make");
                else this.make = "N/A";

                if(this.build.has("model")) this.model = this.build.getString("model");
                else this.model = "N/A";

                if(this.build.has("trim")) this.trim = this.build.getString("trim");
                else this.trim = "N/A";

                if(this.build.has("transmission")) this.transmission = this.build.getString("transmission");
                else this.transmission = "N/A";

                if(this.build.has("drivetrain")) this.drivetype = this.build.getString("drivetrain");
                else this.drivetype = "N/A";

                if(this.build.has("cylinders")) this.cylinders = this.build.getInt("cylinders");
                else this.cylinders = 4;

                if(this.build.has("engine")) this.engine = this.build.getString("engine");
                else this.engine = "N/A";

                if(this.build.has("dist")) this.distance = this.build.getDouble("dist");
                else this.distance = 0;
            }

            if(input.has("dealer"))
            {
                this.dealer = input.getJSONObject("dealer");
                if(this.dealer.has("name")) this.seller_name = capitalizeLetters(this.dealer.getString("name"));
                else this.seller_name = "N/A";

                if(this.dealer.has("city")) this.city = this.dealer.getString("city");
                else this.city = "N/A";

                if(this.dealer.has("state")) this.state = this.dealer.getString("state");
                else this.state = "N/A";
            }

            if(input.has("media"))
            {
                this.img_json = input.getJSONObject("media");
                if(this.img_json.has("photo_links")) this.img_array = this.img_json.getJSONArray("photo_links");
                else this.img_json = null;

                int n = this.img_array.length();
                for(int i=0;i<n;i++)
                {
                    if(i >= 50) break;
                    else
                    {
                        this.images.add(img_array.getString(i));
                    }
                }
            }
        }
        catch(JSONException ex)
        {
            System.out.println("JSON Exception thrown");
        }
    }

    public String capitalizeLetters(String input)
    {
        String[] array = input.split(" ");
        String output = "";
        int n = array.length;
        for(int i=0;i<n;i++)
        {
            String cap = array[i].substring(0, 1).toUpperCase() + array[i].substring(1);
            output += cap;
        }
        return output;
    }

    public void makeHashMap()
    {
        String vehicle_title = Integer.toString(this.year) + this.make + this.model + this.trim;
        String vehicle_information = NumberFormat.getIntegerInstance().format(this.mileage) + " miles | " + this.color + " | " + this.condition + " | $" + NumberFormat.getIntegerInstance().format(this.price);
        String dealer_name = this.seller_name;
        String location = Double.toString(this.distance) + " mi. | " + this.city + ", " + this.state;
        String first_img = this.images.get(0);

        this.listview_hashmap.put("title", vehicle_title);
        this.listview_hashmap.put("information", vehicle_information);
        this.listview_hashmap.put("dealer", dealer_name);
        this.listview_hashmap.put("distance", location);
        this.listview_hashmap.put("first_image", first_img);
    }
}

Answer 1

已解决！有四个主要参数我必须添加到这个 class 才能让它成为 Parcelable。

第一个是接受 Parcel 对象的受保护构造函数。

第二个是一个新的静态 CREATOR 对象，具有内部方法 createFromParcel 和 newArray。

第三个是 describeContents 函数。

最后是 writeToParcel 函数。

希望其他人能够从中吸取教训，如果这可以被视为转贴，我们深表歉意！

修改后的代码如下：

package com.example.marketcheckcarsearchapp;

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

import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;

import java.io.IOException;
import java.io.Serializable;
import java.text.NumberFormat;
import java.util.ArrayList;
import java.util.HashMap;

public class CarListing implements Parcelable
{
    /* vehicle parameters */
    String make, model, trim, vin, color, condition, transmission, engine, drivetype, seller_type, seller_name, website, city, state;
    int year, price, mileage, cylinders;
    double distance;
    ArrayList<String> images;

    /* carfax parameters */
    boolean one_owner, clean_title;

    /* local variables that may be important */
    int index;
    JSONObject img_json, build, dealer;
    JSONArray img_array;

    public HashMap<String, String> listview_hashmap;

    /* Most strings are default N/A. Most integers are default 1, or 1970 for the case of years. */
    public CarListing(JSONObject input, int index)
    {
        try
        {
            this.images = new ArrayList<>();
            this.index = index;
            this.listview_hashmap = new HashMap<>();

            if(input.has("vin")) this.vin = input.getString("vin");
            else this.vin = "N/A";

            if(input.has("price")) this.price = input.getInt("price");
            else this.price = 1;

            if(input.has("mileage")) this.mileage = input.getInt("mileage");
            else this.mileage = 1;

            if(input.has("vdp_url")) this.website = input.getString("vdp_url");
            else this.website = "N/A";

            if(input.has("carfax_1_owner")) this.one_owner = input.getBoolean("carfax_1_owner");
            else this.one_owner = true;

            if(input.has("carfax_clean_title")) this.clean_title = input.getBoolean("carfax_clean_title");
            else this.clean_title = true;

            if(input.has("exterior_color")) this.color = input.getString("exterior_color");
            else this.color = "N/A";

            if(input.has("seller_type")) this.seller_type = input.getString("seller_type");
            else this.seller_type = "N/A";

            if(input.has("inventory_type")) this.condition = input.getString("inventory_type");
            else this.condition = "N/A";

            if(input.has("build"))
            {
                this.build = input.getJSONObject("build");

                if(this.build.has("year")) this.year = this.build.getInt("year");
                else this.year = 1970;

                if(this.build.has("make")) this.make = this.build.getString("make");
                else this.make = "N/A";

                if(this.build.has("model")) this.model = this.build.getString("model");
                else this.model = "N/A";

                if(this.build.has("trim")) this.trim = this.build.getString("trim");
                else this.trim = "N/A";

                if(this.build.has("transmission")) this.transmission = this.build.getString("transmission");
                else this.transmission = "N/A";

                if(this.build.has("drivetrain")) this.drivetype = this.build.getString("drivetrain");
                else this.drivetype = "N/A";

                if(this.build.has("cylinders")) this.cylinders = this.build.getInt("cylinders");
                else this.cylinders = 4;

                if(this.build.has("engine")) this.engine = this.build.getString("engine");
                else this.engine = "N/A";

                if(this.build.has("dist")) this.distance = this.build.getDouble("dist");
                else this.distance = 0;
            }

            if(input.has("dealer"))
            {
                this.dealer = input.getJSONObject("dealer");
                if(this.dealer.has("name")) this.seller_name = capitalizeLetters(this.dealer.getString("name"));
                else this.seller_name = "N/A";

                if(this.dealer.has("city")) this.city = this.dealer.getString("city");
                else this.city = "N/A";

                if(this.dealer.has("state")) this.state = this.dealer.getString("state");
                else this.state = "N/A";
            }

            if(input.has("media"))
            {
                this.img_json = input.getJSONObject("media");
                if(this.img_json.has("photo_links")) this.img_array = this.img_json.getJSONArray("photo_links");
                else this.img_json = null;

                int n = this.img_array.length();
                for(int i=0;i<n;i++)
                {
                    if(i >= 50) break;
                    else
                    {
                        this.images.add(img_array.getString(i));
                    }
                }
            }
        }
        catch(JSONException ex)
        {
            System.out.println("JSON Exception thrown");
        }
    }

    protected CarListing(Parcel in) {
        make = in.readString();
        model = in.readString();
        trim = in.readString();
        vin = in.readString();
        color = in.readString();
        condition = in.readString();
        transmission = in.readString();
        engine = in.readString();
        drivetype = in.readString();
        seller_type = in.readString();
        seller_name = in.readString();
        website = in.readString();
        city = in.readString();
        state = in.readString();
        year = in.readInt();
        price = in.readInt();
        mileage = in.readInt();
        cylinders = in.readInt();
        distance = in.readDouble();
        images = in.createStringArrayList();
        one_owner = in.readByte() != 0;
        clean_title = in.readByte() != 0;
        index = in.readInt();
    }

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

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

    public String capitalizeLetters(String input)
    {
        String[] array = input.split(" ");
        String output = "";
        int n = array.length;
        for(int i=0;i<n;i++)
        {
            String cap = array[i].substring(0, 1).toUpperCase() + array[i].substring(1);
            output += cap;
        }
        return output;
    }

    public void makeHashMap()
    {
        String vehicle_title = Integer.toString(this.year) + this.make + this.model + this.trim;
        String vehicle_information = NumberFormat.getIntegerInstance().format(this.mileage) + " miles | " + this.color + " | " + this.condition + " | $" + NumberFormat.getIntegerInstance().format(this.price);
        String dealer_name = this.seller_name;
        String location = Double.toString(this.distance) + " mi. | " + this.city + ", " + this.state;
        String first_img = this.images.get(0);

        this.listview_hashmap.put("title", vehicle_title);
        this.listview_hashmap.put("information", vehicle_information);
        this.listview_hashmap.put("dealer", dealer_name);
        this.listview_hashmap.put("distance", location);
        this.listview_hashmap.put("first_image", first_img);
    }

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

    @Override
    public void writeToParcel(Parcel dest, int flags) {
        dest.writeString(make);
        dest.writeString(model);
        dest.writeString(trim);
        dest.writeString(vin);
        dest.writeString(color);
        dest.writeString(condition);
        dest.writeString(transmission);
        dest.writeString(engine);
        dest.writeString(drivetype);
        dest.writeString(seller_type);
        dest.writeString(seller_name);
        dest.writeString(website);
        dest.writeString(city);
        dest.writeString(state);
        dest.writeInt(year);
        dest.writeInt(price);
        dest.writeInt(mileage);
        dest.writeInt(cylinders);
        dest.writeDouble(distance);
        dest.writeStringList(images);
        dest.writeByte((byte) (one_owner ? 1 : 0));
        dest.writeByte((byte) (clean_title ? 1 : 0));
        dest.writeInt(index);
    }
}

当使用另一个对象构造自定义对象时，有没有办法使它可打包？

Is there a way to make a custom object parcelable when it is constructed using another object?

java

android

class

parcelable

android-activity