在 Unity 中创建的加载文件下载 iOS 应用程序

Question

我正在尝试加载下载并保存在 iOS 设备的 persistentDataPath 中的 json 文件。下载和保存效果很好。但是我认为我在加载文件时遇到了很大的问题。事实上，当我尝试在 Xcode 中编译项目时，我会收到一些错误消息。

首先是我的 C# 代码：

using UnityEngine;
using System.Collections;
using System.IO;
using System.Net;
using UnityEngine.UI;

public class ReadJson : MonoBehaviour
{
    public Text City;
    public Text Temperature;
    public Image Weather;
    public Text WeatherUrl;

    [System.Serializable]
    public class CityInfo 
    {
        public string name;
    }

    [System.Serializable]
    public class CurrentCondition
    {
        public string date; 
        public string hour; 
        public int tmp; 
        public int wnd_spd; 
        public int wnd_gust; 
        public string wnd_dir; 
        public double pressure; 
        public int humidity; 
        public string condition; 
        public string icon; 
        public string icon_big;
    }

    [System.Serializable]
    public class RootObject
    {
        public CityInfo city_info;
        public CurrentCondition current_condition;
    }

    void Start () {

        WebClient client = new WebClient();
        File.Delete(Path.Combine (Application.persistentDataPath, "myjson.json"));
        client.DownloadFile ("http://www.myjsonurl", Path.Combine (Application.persistentDataPath, "myjson.json"));

        TextAsset asset = Resources.Load (Path.Combine (Application.dataPath + "/Documents", "myjson")) as TextAsset;

        RootObject m = JsonUtility.FromJson<RootObject> (asset.text);

        City.text = m.city_info.name;
        Temperature.text = (m.current_condition.tmp).ToString();

    }
}

现在是 xcode 控制台：

2016-10-21 17:01:20.766001 json[1404:516674] [DYMTLInitPlatform] platform initialization successful

2016-10-21 17:01:20.929950 json[1404:516508] -> registered mono modules 0xb95f70
2016-10-21 17:01:21.356590 json[1404:516508] You've implemented -[<UIApplicationDelegate> application:didReceiveRemoteNotification:fetchCompletionHandler:], but you still need to add "remote-notification" to the list of your supported UIBackgroundModes in your Info.plist.
-> applicationDidFinishLaunching()
2016-10-21 17:01:21.452967 json[1404:516508] Metal GPU Frame Capture Enabled
2016-10-21 17:01:21.453369 json[1404:516508] Metal API Validation Enabled
-> applicationDidBecomeActive()
Init: screen size 750x1334
Initializing Metal device caps
Initialize engine version: 5.3.4f1 (fdbb5133b820)
UnloadTime: 1.705875 ms
Salut/var/mobile/Containers/Data/Application/51A2490E-94EB-4904-9F2E-112AD5632A98/Documents

(Filename: /Users/builduser/buildslave/unity/build/artifacts/generated/common/runtime/UnityEngineDebugBindings.gen.cpp Line: 37)

NullReferenceException: A null value was found where an object instance was required.


(Filename: currently not available on il2cpp Line: -1)

Setting up 1 worker threads for Enlighten.
  Thread -> id: 19f17000 -> priority: 1 

如果有人有想法。提前非常感谢。

Answer 1

您的代码的问题出在这一行：

TextAsset asset = Resources.Load(Path.Combine(Application.dataPath + "/Documents", "myjson")) as TextAsset;

我认为您不了解如何以及何时使用Resources.Load。如果您想使用Resources.Load 功能，您必须从编辑器中创建一个特殊文件夹。此文件夹应位于<ProjectDirectory>/Assets/Resources。您可以仅从编辑器将内容放入/写入此文件夹。在 iOS 上构建后你不能这样做。构建后它变为只读。然后可以使用Resources.Load 函数读取此特殊文件夹。

替换：

TextAsset asset = Resources.Load(Path.Combine(Application.dataPath + "/Documents", "myjson")) as TextAsset;

与

string text = File.ReadAllText(Path.Combine(Application.persistentDataPath, "myjson.json"));
RootObject m = JsonUtility.FromJson<RootObject>(text);
City.text = m.city_info.name;
Temperature.text = (m.current_condition.tmp).ToString();

应该可以解决你的问题。

另一个不应使用的 API 是 WebClient。除非您有充分的理由使用它，否则您不应该使用它。您应该使用WWW 或UnityWebRequest（更新和推荐）API。

如果没有WebClient，您的代码应该是这样的：

void Start()
{
    StartCoroutine(DownloadAndloadJson());
}

IEnumerator DownloadAndloadJson()
{
    string url = "http://www.myjsonurl";

    UnityWebRequest www = UnityWebRequest.Get(url);
    yield return www.Send();

    if (www.isError)
    {
        Debug.Log(www.error);
    }
    else
    {
        //Sucessfully downloaded the Json File
        Debug.Log("Json: " + www.downloadHandler.text);

        string jsonFile = www.downloadHandler.text;

        //Delete old json file. Don't know why but this was in your original code
        File.Delete(Path.Combine(Application.persistentDataPath, "myjson.json"));

        //Save the downloaded data as File
        File.WriteAllText(Path.Combine(Application.persistentDataPath, "myjson.json"), jsonFile);

        //Load the downloaded data 
        string text = File.ReadAllText(Path.Combine(Application.persistentDataPath, "myjson.json"));

        Debug.Log(text);
        RootObject m = JsonUtility.FromJson<RootObject>(text);
        City.text = m.city_info.name;
        Temperature.text = (m.current_condition.tmp).ToString();
    }
}

如果您有问题，请更新到 Unity 5.4。 UnityWebRequest API 应该用于此，它是在 5.3 中引入的，但在 5.4 中修复了错误。您需要using UnityEngine.Networking; 才能使用UnityWebRequest。