Android网络通信必备神器Volley详解——发送一个标准的Request

Volley主要支持一下几种Request

1. StringRequest：确定一个URL，获得返回的原始字符串。

2. ImageRequest：确定一个URL，获得一个图片。

3. JsonObjectRequest和JsonArrayRequest： 确定一个URL，获得JSON对象或者数字。

请求一个图片

使用ImageRequest

ImageView mImageView;
String url = "http://i.imgur.com/7spzG.png";
mImageView = (ImageView) findViewById(R.id.myImage);
...

// Retrieves an image specified by the URL, displays it in the UI.
ImageRequest request = new ImageRequest(url,
    new Response.Listener() {
        @Override
        public void onResponse(Bitmap bitmap) {
            mImageView.setImageBitmap(bitmap);
        }
    }, 0, 0, null,
    new Response.ErrorListener() {
        public void onErrorResponse(VolleyError error) {
            mImageView.setImageResource(R.drawable.image_load_error);
        }
    });
// Access the RequestQueue through your singleton class.
MySingleton.getInstance(this).addToRequestQueue(request);

使用ImageLoader和NetworkImageView

使用ImageLoader 和NetworkImageView来有效的加载多张图片，比如在ListView中加载图片。

在你layout的XML文件中

加载图片

ImageLoader mImageLoader;
NetworkImageView mNetworkImageView;
private static final String IMAGE_URL =
    "http://developer.android.com/images/training/system-ui.png";
...

// Get the NetworkImageView that will display the image.
mNetworkImageView = (NetworkImageView) findViewById(R.id.networkImageView);

// Get the ImageLoader through your singleton class.
mImageLoader = MySingleton.getInstance(this).getImageLoader();

// Set the URL of the image that should be loaded into this view, and
// specify the ImageLoader that will be used to make the request.
mNetworkImageView.setImageUrl(IMAGE_URL, mImageLoader);

正如上篇文章里说的，把RequestQueue封装起来使得图片的cache独立于Activity，当屏幕进行旋转的时候图片不用重新从网络下载，不会造成闪屏。

请求JSON

与前面的Request类似，直接看代码

TextView mTxtDisplay;
ImageView mImageView;
mTxtDisplay = (TextView) findViewById(R.id.txtDisplay);
String url = "http://my-json-feed";

JsonObjectRequest jsObjRequest = new JsonObjectRequest
        (Request.Method.GET, url, null, new Response.Listener() {

    @Override
    public void onResponse(JSONObject response) {
        mTxtDisplay.setText("Response: " + response.toString());
    }
}, new Response.ErrorListener() {

    @Override
    public void onErrorResponse(VolleyError error) {
        // TODO Auto-generated method stub

    }
});

// Access the RequestQueue through your singleton class.
MySingleton.getInstance(this).addToRequestQueue(jsObjRequest);