android 与 php交互 获取复杂json数据 +正在加载效果理解

当时 在解析数据的时候 总是报空指针异常   原因是 由于开启了新的线程，2者单独工作，在获取json数据时  主线程也工作，也就是json数据获取还没结束  主线程便执行

JSONArray jsonArray = new JSONArray(jsonData);    导致  jsonData为空，造成空指针， 解决方法一 在json数据解析之前先判空 即可解决  但是用户体验不好  

解决方法二 是  用正在加载效果，其实很简单，就是先创建 show  然后找一个地方关闭 dismiss（）即可 ，所以只需要用  handler  和message  接受和获取消息，当获取完毕时 发送message消息   获取后  关闭 正在加载并显示数据  即可   ！

代码如下

public class MainActivity extends Activity {String jsonData = null;Button bt;TextView txt;ProgressDialog dialog;private Handler mhandler = new Handler(){@Overridepublic void handleMessage(Message msg) { //用handler 来获取解析结束 并关闭 正在加载 和 显示数据switch (msg.what) {case 1:dialog.dismiss();txt.setText(jsonData);break;default:break;}}};@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);txt= (TextView) findViewById(R.id.txt);bt = (Button) findViewById(R.id.bt);bt.setOnClickListener(new OnClickListener() {@Overridepublic void onClick(View v) { dialog = ProgressDialog.show(MainActivity.this, "正在加载课表...","请稍后..." ,true,true);  //创建正在加载框fun();//try {//JSONArray jsonArray = new JSONArray(jsonData);     //解析json数据//int count = jsonArray.length();//for(int i = 0;i<count;i++){//JSONObject item = jsonArray.getJSONObject(i);////System.out.println(item.optString("content"));//}//} catch (JSONException e) {//e.printStackTrace();//}if(jsonData!=null){try {//System.out.println(jsonData);JSONArray jsonObject = new JSONObject(jsonData).getJSONObject("data").getJSONArray("list");  <span style="font-family: Arial, Helvetica, sans-serif;">//解析json数据</span>//System.out.println(jsonObject.optString("msg"));JSONObject js = jsonObject.getJSONObject(0);System.out.println("------------------>"+js.optString("description")+"----"+js.optString("create_time"));} catch (JSONException e) {e.printStackTrace();}}}});}public void fun(){new Thread(new Runnable() {  @Overridepublic void run() {// TODO Auto-generated method stubHttpClient httpClient = new DefaultHttpClient();HttpGet myGet = new HttpGet(constant.urlArticleString);try {HttpResponse httpResponse = httpClient.execute(myGet);if(httpResponse.getStatusLine().getStatusCode() == HttpStatus.SC_OK){System.out.println("------------->请求成功"+httpResponse.getStatusLine().getStatusCode());HttpEntity entity = httpResponse.getEntity();if (entity != null) {InputStream inputStream = entity.getContent();jsonData = convertStreamToString(inputStream);Message msg = mhandler.obtainMessage(1);mhandler.sendMessage(msg);}}else {System.out.println("--------->请求失败"+httpResponse.getStatusLine().getStatusCode());}} catch (ClientProtocolException e) {e.printStackTrace();} catch (IOException e) {e.printStackTrace();}}}).start();}public static String convertStreamToString(InputStream is) {BufferedReader reader = null;try {reader = new BufferedReader(new InputStreamReader(is, "UTF-8"),// ��ֹģ�����ϵ�����512 * 1024);} catch (UnsupportedEncodingException e1) {e1.printStackTrace();}StringBuilder sb = new StringBuilder();String line = null;try {while ((line = reader.readLine()) != null) {sb.append(line);}} catch (IOException e) {Log.e("DataProvier convertStreamToString", e.getLocalizedMessage(),e);} finally {try {is.close();} catch (IOException e) {e.printStackTrace();}}System.out.println(sb.toString());return sb.toString();}}