Volley的Singleton类有什么用 [英] What is the use of Singleton class in Volley

问题描述

我使用Volley库在Singleton类的帮助下下载图像.
问题:

I used Volley library to download a image with the help of Singleton class.
Problem :

如果使用单一吨级类，则可以一次成功下载图像，并且我还注意到，即使不使用单一吨级类，也可以成功下载图像.

If I used a single ton class I can download a image successfully with in a time and also I noticed that image is downloaded successfully with out using the single ton class also.

请让任何人告诉我，将单例类纳入我的代码有什么好处.

Will you please any one tell me what are the benefits with the singleton class into my code .

---------------------代码具有Singleton类 --------------- -----

---------------------Code With Singleton Class --------------------

MainActivity.java

public class MainActivity extends AppCompatActivity {
    Button response_click;
    TextView text_response;
    RequestQueue requestQueue;
    String server_url="http://i.imgur.com/7spzG.png";
    ImageView imageView;
    ImageRequest imageRequest;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        response_click=(Button) findViewById(R.id.click_response);
        text_response=(TextView) findViewById(R.id.text_response);
        imageView=(ImageView) findViewById(R.id.image_download);
    }//onCreate Ending
    public void response_click(View view){
   
        final ImageRequest imageRequest=new ImageRequest(server_url, new Response.Listener<Bitmap>() {
            @Override
            public void onResponse(Bitmap response) {
                imageView.setImageBitmap(response);
            }
        }, 0, 0, null, new Response.ErrorListener() {
            @Override
            public void onErrorResponse(VolleyError error) {
                Toast.makeText(getApplicationContext(),"You Got an Error....",Toast.LENGTH_LONG).show();

            }
        });
MySingleTon.getInstance(MainActivity.this).addToRequestQue(imageRequest);

    }//Button Click Ending
}//Main Activity Ending

MySingleTon.java

public class MySingleTon {
    private static MySingleTon mySingleTon;
    private RequestQueue requestQueue;
    private static Context mctx;
    private MySingleTon(Context context){
        this.mctx=context;
        this.requestQueue=getRequestQueue();

    }
    public RequestQueue getRequestQueue(){
        if (requestQueue==null){
            requestQueue= Volley.newRequestQueue(mctx.getApplicationContext());
        }
        return requestQueue;
    }
   public static synchronized MySingleTon getInstance(Context context){
       if (mySingleTon==null){
           mySingleTon=new MySingleTon(context);
       }
       return mySingleTon;
   }
    public<T> void addToRequestQue(Request<T> request){
        requestQueue.add(request);

    }
}

在这里，我编写了一个代码，无需使用Singleton类就可以下载图像.请同时检查此代码.
在这里，请记住一件事，在不使用Singleton类的情况下，我也没有任何错误地完成了工作.

Here, I write a code for downloading the image with out using the Singleton class. Please Check this code also.
Here remember one thing, With out using the Singleton class also I done my job with out any errors.

------------------------代码没有Singleton类 ----------- ------------

------------------------code With Out Singleton class -----------------------

MainActivity.java

public class MainActivity extends AppCompatActivity {
    Button response_click;
    TextView text_response;
    RequestQueue requestQueue;
    String server_url="http://i.imgur.com/7spzG.png";
    ImageView imageView;
    ImageRequest imageRequest;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        response_click=(Button) findViewById(R.id.click_response);
        text_response=(TextView) findViewById(R.id.text_response);
        imageView=(ImageView) findViewById(R.id.image_download);
    }//onCreate Ending
    public void response_click(View view){
        requestQueue=Volley.newRequestQueue(this.getApplicationContext());
        final ImageRequest imageRequest=new ImageRequest(server_url, new Response.Listener<Bitmap>() {
            @Override
            public void onResponse(Bitmap response) {
                imageView.setImageBitmap(response);
            }
        }, 0, 0, null, new Response.ErrorListener() {
            @Override
            public void onErrorResponse(VolleyError error) {
                Toast.makeText(getApplicationContext(),"You Got an Error....",Toast.LENGTH_LONG).show();

            }
        });

        requestQueue.add(imageRequest);
        
    }//Button Click Ending
}//Main Activity Ending

推荐答案

如果您的应用程序不断使用网络，则设置单个RequestQueue实例(将持续应用程序的生命周期)可能是最有效的.您可以通过多种方式实现这一目标.推荐的方法是实现一个封装RequestQueue和其他Volley功能的单例类.另一种方法是对Application进行子类化，并在Application.onCreate()中设置RequestQueue.但是不鼓励这种方法.静态单例可以以更模块化的方式提供相同的功能.

If your application makes constant use of the network, it's probably most efficient to set up a single instance of RequestQueue that will last the lifetime of your app. You can achieve this in various ways. The recommended approach is to implement a singleton class that encapsulates RequestQueue and other Volley functionality. Another approach is to subclass Application and set up the RequestQueue in Application.onCreate(). But this approach is discouraged; a static singleton can provide the same functionality in a more modular way.

一个关键的概念是必须使用Application上下文而不是Activity上下文实例化RequestQueue.这样可以确保RequestQueue在您的应用程序的生命周期内持续有效，而不是在每次重新创建活动时(例如，当用户旋转设备时)都重新创建.

A key concept is that the RequestQueue must be instantiated with the Application context, not an Activity context. This ensures that the RequestQueue will last for the lifetime of your app, instead of being recreated every time the activity is recreated (for example, when the user rotates the device).

阅读文档 https://developer.android.com/training/volley/requestqueue.html#singleton

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