JSONArray 使用 Retrofit 库解析并在 ListView 上显示

Question

我目前正在从 Web 服务读取 JSONArray 并将其填充到列表视图中。目前该应用程序没有向我显示任何内容，或者它是否给出任何错误，所以任何人都可以告诉我我做错了什么。提前谢谢你。

这是我的 JSON 文件

{
    "products": [
        {

            "product_name": "wirless charger",
            "product_price": "9.99"

        },
        {
            "product_name": "phone cover ",
            "product_price": "4.99"
        },
        {
            "product_name": "otg cable ",
            "product_price": "2.99"
        }
    ]
}

这是我的接口类

package com.example.productmanager.retrofit;

import com.google.gson.JsonObject;

import org.json.JSONArray;

import java.util.List;

import retrofit2.Call;
import retrofit2.http.FormUrlEncoded;
import retrofit2.http.GET;




 public interface Api {
String BASE_URL = "http://192.168.101.97/productsmanager/products/";
@GET("index.json")
Call<ProductWrapper> getProducts();
}

这是我的产品 POJO 类

package com.example.productmanager.retrofit;

import com.google.gson.annotations.Expose;
import com.google.gson.annotations.SerializedName;


public class Product {


    @SerializedName("product_name")
    @Expose
    private String product_name;

    @SerializedName("product_price")
    @Expose
    private String product_price;


    public String getProduct_name() {
        return product_name;
    }


    public String getProduct_price() {
        return product_price;
    }

}

这是我的产品包装 POJO 类

public class ProductWrapper {

@SerializedName("products")
@Expose
private List<Product> products = null;

public List<Product> getProducts() {
return products;
}

public void setProducts(List<Product> products) {
this.products = products;
}

}

这是我的主要活动课

package com.example.productmanager.retrofit;

import android.Manifest;
import android.content.DialogInterface;
import android.content.Intent;
import android.content.pm.PackageManager;
import android.net.Uri;
import android.support.v4.app.ActivityCompat;
import android.support.v4.content.ContextCompat;
import android.support.v7.app.AlertDialog;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.telephony.TelephonyManager;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.ListAdapter;
import android.widget.ListView;
import android.widget.Toast;

import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
import com.google.gson.JsonParser;
import com.google.gson.JsonSyntaxException;
import com.google.gson.reflect.TypeToken;

import org.json.JSONArray;

import java.lang.reflect.Type;
import java.util.ArrayList;
import java.util.List;

import retrofit2.Call;
import retrofit2.Callback;
import retrofit2.Response;
import retrofit2.Retrofit;
import retrofit2.converter.gson.GsonConverterFactory;

public class MainActivity extends AppCompatActivity {
    private List<product> products = new ArrayList<>();

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

        final ListView productListView = (ListView) findViewById(R.id.productListView);

        Gson gson = new GsonBuilder()
                .setLenient()
                .create();

        Retrofit retrofit = new Retrofit.Builder()
                .baseUrl(Api.BASE_URL)
                .addConverterFactory(GsonConverterFactory.create(gson))
                .build();

        Api api = retrofit.create(Api.class);



Call<ProductWrapper> call = api.getProducts();

call.enqueue(new Callback<ProductWrapper>() {


    @Override
    public void onResponse(Call<ProductWrapper> call, Response<ProductWrapper> response) {
        String productString = response.body().getProducts().toString();

        Type listType = new TypeToken<List<product>>() {}.getType();
        products = getproductList(productString, listType);

        final String[] productName = new String[products.size()];

        for(int i=0; i < products.size(); i++)
        {

            productName[i] = products.get(i).getproduct_name();

        }

        productListView.setAdapter(new ArrayAdapter<String>(
                getApplicationContext(),
                R.layout.support_simple_spinner_dropdown_item,
                productName
        ));

    }

    @Override
    public void onFailure(Call<ProductWrapper> call, Throwable t) {
        Toast.makeText(getApplicationContext(), t.getMessage(), Toast.LENGTH_LONG).show();
    }
});

            }




    }

    public static <T> List<T> getproductList(String productString, Type listType) {
        if (!isValid(productString)){
            return null;

        }
        return new Gson().fromJson(productString, listType);
    }

    private static boolean isValid(String productString) {
        try{
            new JsonParser().parse(productString);
            return true;

        }catch (JsonSyntaxException jse){
            return false;
        }
    }
}

和我的 MainActivity xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="com.example.productManager.retrofit.MainActivity">

    <ListView
        android:id="@+id/clientListView"
        android:cacheColorHint="#000"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"></ListView>


</RelativeLayout>

这是我的错误日志

E/AndroidRuntime: FATAL EXCEPTION: main
                  Process: com.example.productmanager.retrofit, PID: 3628
                  com.google.gson.JsonSyntaxException: java.lang.IllegalStateException: Expected BEGIN_OBJECT but was STRING at line 1 column 2 path $[0]
                      at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.read(ReflectiveTypeAdapterFactory.java:224)
                      at com.google.gson.internal.bind.TypeAdapterRuntimeTypeWrapper.read(TypeAdapterRuntimeTypeWrapper.java:41)
                      at com.google.gson.internal.bind.CollectionTypeAdapterFactory$Adapter.read(CollectionTypeAdapterFactory.java:82)
                      at com.google.gson.internal.bind.CollectionTypeAdapterFactory$Adapter.read(CollectionTypeAdapterFactory.java:61)
                      at com.google.gson.Gson.fromJson(Gson.java:888)
                      at com.google.gson.Gson.fromJson(Gson.java:853)
                      at com.google.gson.Gson.fromJson(Gson.java:802)
                      at com.example.productmanager.retrofit.MainActivity.getProductsList(MainActivity.java:121)
                      at com.example.productmanager.retrofit.MainActivity$1.onResponse(MainActivity.java:87)
                      at retrofit2.ExecutorCallAdapterFactory$ExecutorCallbackCall$1$1.run(ExecutorCallAdapterFactory.java:70)
                      at android.os.Handler.handleCallback(Handler.java:751)
                      at android.os.Handler.dispatchMessage(Handler.java:95)
                      at android.os.Looper.loop(Looper.java:154)
                      at android.app.ActivityThread.main(ActivityThread.java:6776)
                      at java.lang.reflect.Method.invoke(Native Method)
                      at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1496)
                      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1386)
                   Caused by: java.lang.IllegalStateException: Expected BEGIN_OBJECT but was STRING at line 1 column 2 path $[0]
                      at com.google.gson.stream.JsonReader.beginObject(JsonReader.java:385)
                      at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.read(ReflectiveTypeAdapterFactory.java:213)
                      at com.google.gson.internal.bind.TypeAdapterRuntimeTypeWrapper.read(TypeAdapterRuntimeTypeWrapper.java:41) 
                      at com.google.gson.internal.bind.CollectionTypeAdapterFactory$Adapter.read(CollectionTypeAdapterFactory.java:82) 
                      at com.google.gson.internal.bind.CollectionTypeAdapterFactory$Adapter.read(CollectionTypeAdapterFactory.java:61) 
                      at com.google.gson.Gson.fromJson(Gson.java:888) 
                      at com.google.gson.Gson.fromJson(Gson.java:853) 
                      at com.google.gson.Gson.fromJson(Gson.java:802) 
                      at com.example.productmanager.retrofit.MainActivity.getProductsList(MainActivity.java:121) 
                      at com.example.productmanager.retrofit.MainActivity$1.onResponse(MainActivity.java:87) 
                      at retrofit2.ExecutorCallAdapterFactory$ExecutorCallbackCall$1$1.run(ExecutorCallAdapterFactory.java:70) 
                      at android.os.Handler.handleCallback(Handler.java:751) 
                      at android.os.Handler.dispatchMessage(Handler.java:95) 
                      at android.os.Looper.loop(Looper.java:154) 
                      at android.app.ActivityThread.main(ActivityThread.java:6776) 
                      at java.lang.reflect.Method.invoke(Native Method) 
                      at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1496) 
                      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1386) 
Device samsung-sm_j530f-5200fedcb478154bdisconnected, monitoring stopped.
Application terminated.

Answer 1

Android hive 为初学者提供了一些很好的教程。 :)

Answer 2

你还需要一个像这样的 pojo 类

    public class ProductWrapper {

@SerializedName("products")
@Expose
private List<Product> products = null;

public List<Product> getProducts() {
return products;
}

public void setProducts(List<Product> products) {
this.products = products;
}

}

对于Product，使用您已经创建的类。然后像下面这样调用

Call<ProductWrapper> call = api.getProducts();

    call.enqueue(new Callback<ProductWrapper>() {


        @Override
        public void onResponse(Call<ProductWrapper> call, Response<ProductWrapper> response) {
            String productString = response.body().getProducts().toString();

            Type listType = new TypeToken<List<product>>() {}.getType();
            products = getproductList(productString, listType);

            final String[] productName = new String[products.size()];

            for(int i=0; i < products.size(); i++)
            {

                productName[i] = products.get(i).getproduct_name();

            }

            productListView.setAdapter(new ArrayAdapter<String>(
                    getApplicationContext(),
                    R.layout.support_simple_spinner_dropdown_item,
                    productName
            ));

        }

        @Override
        public void onFailure(Call<ProductWrapper> call, Throwable t) {
            Toast.makeText(getApplicationContext(), t.getMessage(), Toast.LENGTH_LONG).show();
        }
    });

并像这样更改您的服务调用

public interface Api {
String BASE_URL = "http://192.168.101.97/productsmanager/products/";
@GET("index.json")
Call<ProductWrapper> getProducts();
}