向Android项目添加应用程序控制器？

Question

向Android项目添加应用程序控制器？

3

我在跟随一份安卓教程学习，但是它总是崩溃，我觉得我没有正确地包含Application类。我需要进一步检查logcat，但是首先想确认代码是否被正确实现。

app/java/co.mystuff.CoolApp/MainActivity.java

以下链接提供了使用Volley进行安卓异步HTTP请求的教程：http://arnab.ch/blog/2013/08/asynchronous-http-requests-in-android-using-volley/

package co.mystuff.CoolApp;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.TextView;

import com.android.volley.Request;
import com.android.volley.RequestQueue;
import com.android.volley.Response;
import com.android.volley.VolleyError;
import com.android.volley.VolleyLog;
import com.android.volley.toolbox.JsonObjectRequest;
import com.android.volley.toolbox.StringRequest;
import com.android.volley.toolbox.Volley;

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


public class MainActivity extends AppCompatActivity {

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


        // Make call
        final String URL = "http://api.dribbble.com/shots/everyone";
        // pass second argument as "null" for GET requests
        JsonObjectRequest req = new JsonObjectRequest(URL, null,
                new Response.Listener<JSONObject>() {
                    @Override
                    public void onResponse(JSONObject response) {
                        try {
                            VolleyLog.v("Response:%n %s", response.toString(4));
                        } catch (JSONException e) {
                            e.printStackTrace();
                        }
                    }
                }, new Response.ErrorListener() {
            @Override
            public void onErrorResponse(VolleyError error) {
                VolleyLog.e("Error: ", error.getMessage());
            }
        });

        // add the request object to the queue to be executed
        ApplicationController.getInstance().addToRequestQueue(req);


    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.menu_main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }
}

app/java/co.mystuff.CoolApp/ApplicationController.java

package co.mystuff.CoolApp;

import android.app.Application;
import android.text.TextUtils;

import com.android.volley.Request;
import com.android.volley.RequestQueue;
import com.android.volley.VolleyLog;
import com.android.volley.toolbox.Volley;

/**
 * Created by Michael on 6/17/2015.
 */
public class ApplicationController extends Application {

    /**
     * Log or request TAG
     */
    public static final String TAG = "VolleyPatterns";

    /**
     * Global request queue for Volley
     */
    private RequestQueue mRequestQueue;

    /**
     * A singleton instance of the application class for easy access in other places
     */
    private static ApplicationController sInstance;

    @Override
    public void onCreate() {
        super.onCreate();

        // initialize the singleton
        sInstance = this;
    }

    /**
     * @return co.pixelmatter.meme.ApplicationController singleton instance
     */
    public static synchronized ApplicationController getInstance() {
        return sInstance;
    }

    /**
     * @return The Volley Request queue, the queue will be created if it is null
     */
    public RequestQueue getRequestQueue() {
        // lazy initialize the request queue, the queue instance will be
        // created when it is accessed for the first time
        if (mRequestQueue == null) {
            mRequestQueue = Volley.newRequestQueue(getApplicationContext());
        }

        return mRequestQueue;
    }

    /**
     * Adds the specified request to the global queue, if tag is specified
     * then it is used else Default TAG is used.
     *
     * @param req
     * @param tag
     */
    public <T> void addToRequestQueue(Request<T> req, String tag) {
        // set the default tag if tag is empty
        req.setTag(TextUtils.isEmpty(tag) ? TAG : tag);

        VolleyLog.d("Adding request to queue: %s", req.getUrl());

        getRequestQueue().add(req);
    }

    /**
     * Adds the specified request to the global queue using the Default TAG.
     *
     * @param req
     * @param tag
     */
    public <T> void addToRequestQueue(Request<T> req) {
        // set the default tag if tag is empty
        req.setTag(TAG);

        getRequestQueue().add(req);
    }

    /**
     * Cancels all pending requests by the specified TAG, it is important
     * to specify a TAG so that the pending/ongoing requests can be cancelled.
     *
     * @param tag
     */
    public void cancelPendingRequests(Object tag) {
        if (mRequestQueue != null) {
            mRequestQueue.cancelAll(tag);
        }
    }
}

- Michael Joseph Aubry

2

你是否将Controller添加到了应用程序清单中？否则，由于getInstance将返回null，您将收到一个空指针异常。 - fmt.Println.MKO

我没有触碰清单。 - Michael Joseph Aubry

我该如何将Java控制器添加到清单中？我是个新手，但正在学习。我模糊地记得需要添加到清单中。 - Michael Joseph Aubry

在你的应用程序元素中添加属性名称，将其作为minifest中的一个属性。你需要提供完整的路径，因此包名和类名都要写全。'<application android:name="YOUR_Controller"....' - fmt.Println.MKO

1个回答

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- chiragjn · Accepted Answer

我不能评论，但是你是否已经将以下代码添加到你的清单文件中？

<application
    android:name="co.mystuff.CoolApp.ApplicationController"
...
/>