Question

我不知道该做什么以及问题来自哪里。我已经尝试了各种方案来获得解决方案，但似乎没有任何结果。这是错误输出：

06-09 14:33:44.082 3383-3383/wait.com.linasblog E/AndroidRuntime: FATAL EXCEPTION: main
Process: wait.com.linasblog, PID: 3383
java.lang.RuntimeException: Unable to start activity ComponentInfo{wait.com.linasblog/wait.com.linasblog.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void wait.com.linasblog.AppController.addToRequestQueue(com.android.volley.Request)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2416)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
at android.app.ActivityThread.-wrap11(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void wait.com.linasblog.AppController.addToRequestQueue(com.android.volley.Request)' on a null object reference
at wait.com.linasblog.MainActivity.getJsonPosts(MainActivity.java:208)
at wait.com.linasblog.MainActivity.onCreate(MainActivity.java:42)
at android.app.Activity.performCreate(Activity.java:6237)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1107)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2369)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476) 
at android.app.ActivityThread.-wrap11(ActivityThread.java) 
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344) 
at android.os.Handler.dispatchMessage(Handler.java:102) 
at android.os.Looper.loop(Looper.java:148) 
at android.app.ActivityThread.main(ActivityThread.java:5417) 
at java.lang.reflect.Method.invoke(Native Method) 
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)

这是我的请求方法：

public void getJsonPosts(){


        RequestSingleton.getInstance(this.getApplicationContext()).getRequestQueue();
     //  RequestQueue queue = RequestSingleton.getInstance(this.getApplicationContext()).getRequestQueue();
//        queue.start();
        String url = "http://linagrey.blogspot.com/feeds/posts/default?alt=json";


        JsonObjectRequest jsonRequest = new JsonObjectRequest(Request.Method.GET,url,null, new Response.Listener<JSONObject>() {
            @Override
            public void onResponse(JSONObject response) {
                try {
                    JSONObject feedResponse =  response.getJSONObject("feed");
                    JSONArray entryArrayPosts = feedResponse.getJSONArray("entry");
                    BlogPost bp;
                    for (int i = 0; i < entryArrayPosts.length(); i++){
                        bp = new BlogPost();
                        //Get the entry as an array and loop through
                        JSONObject entryBlogPost = entryArrayPosts.getJSONObject(i);

                        //Get the title from the array
                        JSONObject postObject = entryBlogPost.getJSONObject("title");
                        //JSONObject postHtmlContent = entryBlogPost.getJSONObject(KEYS.POST_JSON_OBJECT_HTML_CONTENT);

                        //GET LINK ARRAY FROM JSON
                        JSONArray linkAddress = entryBlogPost.getJSONArray(KEYS.POST_JSON_ARRAY_OBJECT);

                        if(entryBlogPost.has(KEYS.MEDIA_THUMBNAIL)) {
                            JSONObject imageObjectUrl = entryBlogPost.getJSONObject(KEYS.MEDIA_THUMBNAIL);
                            String thumbnailUrl = imageObjectUrl.getString(KEYS.MEDIA_THUMBNAIL_URL);
                            bp.setmUrlThumbnail(thumbnailUrl);
                        }

                        //for loop for link array object
                        for (int j = 0;j < linkAddress.length(); j++){
                            JSONObject eachLink = linkAddress.getJSONObject(4);
                            String htmlUrl = eachLink.getString(KEYS.POST_HTML_LINK);
                            bp.setmLinkContent(htmlUrl);
                        }


                        //Get title string contained in Title Object
                        String title = postObject.getString(KEYS.POST_TITLE);
                        Log.v(TAG, "OBJECTS HAVE THIS PROPERTIES: " + i + " " + title);


                        //Set Properties Gotten
                        bp.setmTitle(title);

                        Log.v(TAG, "OBJECTS HAVE THIS PROPERTIES: " + i + " " + bp.toString());
                        //Add a blog post Object to the Arraylist
                        postArrayList.add(bp);


                    }
                   // Log.v(TAG, "Arraylist SIZE " + postArrayList.size());

                    for(BlogPost posts : postArrayList){
                        Log.v(TAG, posts + " ");
                    }

                    // Toast.makeText(this.,response.toString(),Toast.LENGTH_LONG).show();

                }catch(JSONException e){
                    Log.v(TAG, e.toString());
                }
            }
        },new Response.ErrorListener(){
            @Override
            public void onErrorResponse(VolleyError error) {
                Log.v(TAG, error.toString());
            }
        });
        RequestSingleton.getInstance(this).addToRequestQueue(jsonRequest);
     }

这是我的Singleton类：

public class RequestSingleton {

    private static RequestSingleton mInstance ;
    private RequestQueue mRequestQueue;
    private ImageLoader mImageLoader;
    private static Context mCtx;

        private RequestSingleton(Context context){
            mCtx = context;
            mRequestQueue = getRequestQueue();

            mImageLoader = new ImageLoader(mRequestQueue, new ImageLoader.ImageCache(){

                private final LruCache<String, Bitmap> cache = new LruCache<String, Bitmap>(20);

                @Override
                public Bitmap getBitmap(String url) {
                    return cache.get(url);
                }

                @Override
                public void putBitmap(String url, Bitmap bitmap) {
                    cache.put(url, bitmap);
                }
            });
        }

    public static synchronized RequestSingleton getInstance(Context context){
        if (mInstance == null){
            mInstance = new RequestSingleton(context);
        }
        return mInstance;
    }

    public RequestQueue getRequestQueue(){
        if(mRequestQueue == null){
            mRequestQueue = Volley.newRequestQueue(mCtx.getApplicationContext());
        }
        return mRequestQueue;
    }

    public <T> void addToRequestQueue(Request<T> req){
        getRequestQueue().add(req);
    }
    public ImageLoader getImageLoader(){
        return mImageLoader;
    }




}

这是清单文件：

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="wait.com.linasblog">

    <uses-permission android:name = "android.permission.INTERNET"/>
    <uses-permission android:name= "android.permission.ACCESS_NETWORK_STATE"/>

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        android:name = ".RequestSingleton"

        <activity
            android:name=".MainActivity"
            android:label="@string/app_name"
            android:theme="@style/AppTheme.NoActionBar">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>

Answer 1

在您的RequestSingleton中，您将获得

上的空值

public <T> void addToRequestQueue(Request<T> req){ 
        getRequestQueue().add(req);
    }

正如您将在错误日志中看到的那样，在日志中显示了一半。

单例类，主要活动不获取数据而不解析jsonrequest

1 个答案: