Android 中常用代码片段

一：AsyncTask 的使用

（1）activity_main.xml

<TextView
        android:id="@+id/tvInfo"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/hello_world" />

<ProgressBar
         android:layout_below="@id/tvInfo"
         android:id="@+id/asyncPb"
         style="?android:attr/progressBarStyleHorizontal"
         android:layout_width="fill_parent"
         android:layout_height="wrap_content"
         android:visibility="gone" />

（2）MainActivity.java

public class MainActivity extends Activity {
	private ProgressBar asyncPb = null;
	private TextView tvInfo = null;

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

		tvInfo = (TextView)findViewById(R.id.tvInfo);

		String params = "Welcome to here";
		new MyAsyncTask().execute(params);
	}

	private class MyAsyncTask extends AsyncTask<String, Integer, String>{
		@Override
        protected void onPreExecute() {
        	//做一些预处理
			asyncPb = (ProgressBar)findViewById(R.id.asyncPb);
			asyncPb.setVisibility(View.VISIBLE);
        }

		@Override
		protected String doInBackground(String... params) {
			//执行耗时操作，网络任务、文件操作、数据库操作、复杂计算操作
			int myProgress = 0;
			int length = params[0].length();

			for(int i=1; i<=length; i++){
				myProgress = i;
				//模拟耗时操作
				try {
					Thread.sleep(300);
				} catch (InterruptedException e) {
					e.printStackTrace();
				}
				publishProgress((int)((myProgress/(float)length)*100));
			}

			//它将传递给onPostExecute
			return params[0];
		}

		@Override
		protected void onProgressUpdate(Integer... values) {
			//更新进度条
			asyncPb.setProgress(values[0]);
			tvInfo.setText("已加载："+(values[0])+"%");
		}

		@Override
		protected void onPostExecute(String result) {
			//更新UI
			tvInfo.setText("加载完成："+result);
		}
	}
}

　二：HttpGet

public static String getRequest(String url){
        String result = "";
        HttpClient client = new DefaultHttpClient();

        HttpGet get = new HttpGet(url);

        try {
            HttpParams httpParams = client.getParams();

            HttpConnectionParams.setConnectionTimeout(httpParams, 3000);
            HttpConnectionParams.setSoTimeout(httpParams, 5000);

            HttpResponse response = client.execute(get);

            if(response.getStatusLine().getStatusCode() == HttpStatus.SC_OK){
                result = EntityUtils.toString(response.getEntity()).trim();
            }
        } catch (Exception e) {
            //连接超时
        } 

        return result;
    }

三：Volley POST

private RequestQueue rQueue = null;

rQueue = WzhVolley.getRequestQueue();

StringRequest postRequest = new StringRequest(
    Request.Method.POST,
    URL,
    createDoSuccess(),
    createDoError()){
        protected Map<String,String> getParams(){
            Map<String,String> params = new HashMap<String,String>();
            params.put(key,value);
            return params;
        }
    };

postRequest.setRetryPolicy(new
    DefaultRetryPolicy(WR.DEFAULT_TIMEOUT_MS, WR.DEFAULT_MAX_RETRIES, WR.DEFAULT_BACKOFF_MULT));
rQueue.add(postRequest);

private Response.Listener<String> createDoSuccess(){
    return new Response.Listener<String>(){
        public void onResponse(String arg0){
            //...
            JSONObject jsonObj = new JSONObject(arg0);
            //or
            JSONArray jsonArr = new JSONArray(arg0);
        }
    };
}
private Response.ErrorListener createDoError(){
    return new Response.ErrorListener(){
        public void onErrorResponse(VolleyError arg0){
            //...
        }
    };
}