Android(安卓)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;@Overrideprotected 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);        }@Overrideprotected 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onPostExecutereturn params[0];}@Overrideprotected void onProgressUpdate(Integer... values) {//更新进度条asyncPb.setProgress(values[0]);tvInfo.setText("已加载："+(values[0])+"%");}@Overrideprotected void onPostExecute(String result) {//更新UItvInfo.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){            //...        }    };}

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