我是Android应用程序开发的新手，我正在尝试开发一个有效的应用程序。但是我创建的这个页面因为它已经被创建而给出了问题，我真的希望有人可以帮助我。每次运行此程序时，应用程序力都会关闭。
这是源代码：
public class Latest extends ListActivity {
// Progress Dialog
private ProgressDialog pDialog;
// Creating JSON Parser object
JSONParser jParser = new JSONParser();
ArrayList<HashMap<String, String>> eventsList;
// url to get all products list
private static String url_all_products = "http://";
// JSON Node names
private static final String TAG_SUCCESS = "success";
private static final String TAG_BOOKS = "books";
private static final String TAG_TITLE = "title";
private static final String TAG_AUTHOR = "author";
private static final String TAG_DESCRIPTION = "description";
private static final String TAG_PRICE = "price";
private static final String TAG_DISCOUNT = "discount";
private static final String TAG_CATEGORY = "category";
private static final String TAG_PID = "pid";
// products JSONArray
JSONArray events = null;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_latest);
// Hashmap for ListView
eventsList = new ArrayList<HashMap<String, String>>();
// Loading products in Background Thread
new LoadAllProducts().execute();
// Get listview
// ListView lv = getListView();
}
// Response from Edit Product Activity
@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
super.onActivityResult(requestCode, resultCode, data);
// if result code 100
if (resultCode == 100) {
// if result code 100 is received
// means user edited/deleted product
// reload this screen again
Intent intent = getIntent();
finish();
startActivity(intent);
}
}
/**
* Background Async Task to Load all product by making HTTP Request
* */
class LoadAllProducts extends AsyncTask<String, String, String> {
/**
* Before starting background thread Show Progress Dialog
* */
@Override
protected void onPreExecute() {
super.onPreExecute();
pDialog = new ProgressDialog(Latest.this);
pDialog.setMessage("Loading Books. Please wait...");
pDialog.setIndeterminate(false);
pDialog.setCancelable(false);
pDialog.show();
}
/**
* getting All products from url
* */
protected String doInBackground(String... args) {
// Building Parameters
List<NameValuePair> params = new ArrayList<NameValuePair>();
// getting JSON string from URL
JSONObject json = jParser.makeHttpRequest(url_all_products, "GET", params);
// Check your log cat for JSON reponse
Log.d("All Products: ", json.toString());
try {
// Checking for SUCCESS TAG
int success = json.getInt(TAG_SUCCESS);
if (success == 1) {
// products found
// Getting Array of Products
events = json.getJSONArray(TAG_BOOKS);
// looping through All Products
for (int i = events.length()-1; i > events.length()-4; i--) {
JSONObject c = events.getJSONObject(i);
// Storing each json item in variable
String pid = c.getString(TAG_PID);
String title = c.getString(TAG_TITLE);
String author = "Author :" +c.getString(TAG_AUTHOR);
String description = c.getString(TAG_DESCRIPTION);
String price = "Price :" +c.getString(TAG_PRICE);
String discount = "Discount : " +c.getString(TAG_DISCOUNT);
String category = "Category :" +c.getString(TAG_CATEGORY);
// creating new HashMap
HashMap<String, String> map = new HashMap<String, String>();
// adding each child node to HashMap key => value
map.put(TAG_PID, pid);
map.put(TAG_TITLE, title);
map.put(TAG_AUTHOR, author);
map.put(TAG_DESCRIPTION, description);
map.put(TAG_PRICE, price);
map.put(TAG_DISCOUNT, discount);
map.put(TAG_CATEGORY, category);
// adding HashList to ArrayList
eventsList.add(map);
}
}
} catch (JSONException e) {
e.printStackTrace();
}
return null;
}
/**
* After completing background task Dismiss the progress dialog
* **/
protected void onPostExecute(String file_url) {
// dismiss the dialog after getting all products
pDialog.dismiss();
// updating UI from Background Thread
runOnUiThread(new Runnable() {
public void run() {
/**
* Updating parsed JSON data into ListView
* */
ListAdapter adapter = new SimpleAdapter(
Latest.this, eventsList,
R.layout.list_item2, new String[] { TAG_PID, TAG_TITLE, TAG_AUTHOR, TAG_DESCRIPTION, TAG_PRICE, TAG_DISCOUNT, TAG_DESCRIPTION},
new int[] { R.id.pid, R.id.title, R.id.author,R.id.description, R.id.price, R.id.discount,R.id.category });
// updating listview
setListAdapter(adapter);
}
});
}
}
}
这是LogCat（错误）：
Buffer Error(1024): Error converting result java.lang.NullPointerException: lock == null
JSON Parser(1024): Error parsing data org.json.JSONException: End of input at character 0 of
AndroidRuntime(1024): FATAL EXCEPTION: AsyncTask #1
AndroidRuntime(1024): java.lang.RuntimeException: An error occured while executing doInBackground()
AndroidRuntime(1024): at android.os.AsyncTask$3.done(AsyncTask.java:299)
AndroidRuntime(1024): at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:352)
AndroidRuntime(1024): at java.util.concurrent.FutureTask.setException(FutureTask.java:219)
AndroidRuntime(1024): at java.util.concurrent.FutureTask.run(FutureTask.java:239)
AndroidRuntime(1024): at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1080)
AndroidRuntime(1024): at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:573)
AndroidRuntime(1024): at java.lang.Thread.run(Thread.java:856)
AndroidRuntime(1024): Caused by: java.lang.NullPointerException
AndroidRuntime(1024): at com.spyraa.bookstore.Latest$LoadAllProducts.doInBackground(Latest.java:113)
AndroidRuntime(1024): at com.spyraa.bookstore.Latest$LoadAllProducts.doInBackground(Latest.java:1)
AndroidRuntime(1024): at android.os.AsyncTask$2.call(AsyncTask.java:287)
AndroidRuntime(1024): at java.util.concurrent.FutureTask.run(FutureTask.java:234)
AndroidRuntime(1024): ... 3 more
这是JSONParser类：
public class JSONParser {
private static final String TAG = "JSONParser";
static InputStream is = null;
static JSONObject jObj = null;
static String json = "";
// constructor
public JSONParser() {
}
// function get json from url
// by making HTTP POST or GET method
public JSONObject makeHttpRequest(String url, String method,
List<NameValuePair> params) {
// Making HTTP request
try{
// check for request method
if(method == "POST"){
Log.d(TAG, "method=POST");
// request method is POST
// defaultHttpClient
DefaultHttpClient httpClient = new DefaultHttpClient();
Log.d(TAG, "url=" + url);
HttpPost httpPost = new HttpPost(url);
httpPost.setEntity(new UrlEncodedFormEntity(params));
HttpResponse httpResponse = httpClient.execute(httpPost);
HttpEntity httpEntity = httpResponse.getEntity();
is = httpEntity.getContent();
}else if(method == "GET"){
Log.d(TAG, "method=GET");
// request method is GET
DefaultHttpClient httpClient = new DefaultHttpClient();
String paramString = URLEncodedUtils.format(params, "utf-8");
url += "?" + paramString;
Log.d(TAG, "url=" + url);
HttpGet httpGet = new HttpGet(url);
HttpResponse httpResponse = httpClient.execute(httpGet);
HttpEntity httpEntity = httpResponse.getEntity();
is = httpEntity.getContent();
}
Log.d(TAG, "HTTP request done");
} catch (UnsupportedEncodingException e) {
Log.d(TAG, "UNSUPPORTED ENCODING: ", e);
} catch (ClientProtocolException e) {
Log.d(TAG, "CLIENT PROTOCOL: ", e);
} catch (IOException e) {
Log.d(TAG, "IO EXCEPTION: ", e);
}
try {
Log.d(TAG, "Extract response");
BufferedReader reader = new BufferedReader(new InputStreamReader(
is, "iso-8859-1"), 8);
StringBuilder sb = new StringBuilder();
String line = null;
while ((line = reader.readLine()) != null) {
Log.d(TAG, "line=" + line);
sb.append(line + "\n");
}
is.close();
json = sb.toString();
Log.d(TAG, "json=" + json);
} catch (Exception e) {
Log.d(TAG, "Exception: ", e);
Log.e("Buffer Error", "Error converting result " + e.toString());
}
// try parse the string to a JSON object
try {
Log.d(TAG, "Parse JSON");
jObj = new JSONObject(json);
} catch (JSONException e) {
Log.d(TAG, "JSONException: ", e);
Log.e("JSON Parser", "Error parsing data " + e.toString());
}
// return JSON String
return jObj;
}
}
这是最近的logcat：
03-19 12:44:55.985: D/dalvikvm(919): GC_CONCURRENT freed 338K, 15% free 2791K/3268K, paused 111ms+119ms, total 437ms
03-19 12:45:10.246: D/dalvikvm(919): GC_CONCURRENT freed 373K, 16% free 2815K/3324K, paused 110ms+100ms, total 551ms
03-19 12:45:11.366: D/JSONParser(919): IO EXCEPTION:
03-19 12:45:11.366: D/JSONParser(919): org.apache.http.conn.HttpHostConnectException: Connection to http:// refused
03-19 12:45:11.366: D/JSONParser(919): at org.apache.http.impl.conn.DefaultClientConnectionOperator.openConnection(DefaultClientConnectionOperator.java:183)
03-19 12:45:11.366: D/JSONParser(919): at org.apache.http.impl.conn.AbstractPoolEntry.open(AbstractPoolEntry.java:164)
03-19 12:45:11.366: D/JSONParser(919): at org.apache.http.impl.conn.AbstractPooledConnAdapter.open(AbstractPooledConnAdapter.java:119)
03-19 12:45:11.366: D/JSONParser(919): at org.apache.http.impl.client.DefaultRequestDirector.execute(DefaultRequestDirector.java:360)
03-19 12:45:11.366: D/JSONParser(919): at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:555)
03-19 12:45:11.366: D/JSONParser(919): at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:487)
03-19 12:45:11.366: D/JSONParser(919): at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:465)
03-19 12:45:11.366: D/JSONParser(919): at com.spyraa.bookstore.JSONParser.makeHttpRequest(JSONParser.java:66)
03-19 12:45:11.366: D/JSONParser(919): at com.spyraa.bookstore.Latest$LoadAllProducts.doInBackground(Latest.java:105)
03-19 12:45:11.366: D/JSONParser(919): at com.spyraa.bookstore.Latest$LoadAllProducts.doInBackground(Latest.java:1)
03-19 12:45:11.366: D/JSONParser(919): at android.os.AsyncTask$2.call(AsyncTask.java:287)
03-19 12:45:11.366: D/JSONParser(919): at java.util.concurrent.FutureTask.run(FutureTask.java:234)
03-19 12:45:11.366: D/JSONParser(919): at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1080)
03-19 12:45:11.366: D/JSONParser(919): at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:573)
03-19 12:45:11.366: D/JSONParser(919): at java.lang.Thread.run(Thread.java:856)
03-19 12:45:11.366: D/JSONParser(919): Caused by: java.net.ConnectException: failed to connect to http/1 (port 80): connect failed: ECONNREFUSED (Connection refused)
03-19 12:45:11.366: D/JSONParser(919): at libcore.io.IoBridge.connect(IoBridge.java:114)
03-19 12:45:11.366: D/JSONParser(919): at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:192)
03-19 12:45:11.366: D/JSONParser(919): at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:459)
03-19 12:45:11.366: D/JSONParser(919): at java.net.Socket.connect(Socket.java:842)
03-19 12:45:11.366: D/JSONParser(919): at org.apache.http.conn.scheme.PlainSocketFactory.connectSocket(PlainSocketFactory.java:119)
03-19 12:45:11.366: D/JSONParser(919): at org.apache.http.impl.conn.DefaultClientConnectionOperator.openConnection(DefaultClientConnectionOperator.java:144)
03-19 12:45:11.366: D/JSONParser(919): ... 14 more
03-19 12:45:11.366: D/JSONParser(919): Caused by: libcore.io.ErrnoException: connect failed: ECONNREFUSED (Connection refused)
03-19 12:45:11.366: D/JSONParser(919): at libcore.io.Posix.connect(Native Method)
03-19 12:45:11.366: D/JSONParser(919): at libcore.io.BlockGuardOs.connect(BlockGuardOs.java:85)
03-19 12:45:11.366: D/JSONParser(919): at libcore.io.IoBridge.connectErrno(IoBridge.java:127)
03-19 12:45:11.366: D/JSONParser(919): at libcore.io.IoBridge.connect(IoBridge.java:112)
03-19 12:45:11.366: D/JSONParser(919): ... 19 more
03-19 12:45:11.499: D/JSONParser(919): Extract response
03-19 12:45:12.838: D/JSONParser(919): Exception:
03-19 12:45:12.838: D/JSONParser(919): java.lang.NullPointerException: lock == null
03-19 12:45:12.838: D/JSONParser(919): at java.io.Reader.<init>(Reader.java:64)
03-19 12:45:12.838: D/JSONParser(919): at java.io.InputStreamReader.<init>(InputStreamReader.java:79)
03-19 12:45:12.838: D/JSONParser(919): at com.spyraa.bookstore.JSONParser.makeHttpRequest(JSONParser.java:83)
03-19 12:45:12.838: D/JSONParser(919): at com.spyraa.bookstore.Latest$LoadAllProducts.doInBackground(Latest.java:105)
03-19 12:45:12.838: D/JSONParser(919): at com.spyraa.bookstore.Latest$LoadAllProducts.doInBackground(Latest.java:1)
03-19 12:45:12.838: D/JSONParser(919): at android.os.AsyncTask$2.call(AsyncTask.java:287)
03-19 12:45:12.838: D/JSONParser(919): at java.util.concurrent.FutureTask.run(FutureTask.java:234)
03-19 12:45:12.838: D/JSONParser(919): at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1080)
03-19 12:45:12.838: D/JSONParser(919): at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:573)
03-19 12:45:12.838: D/JSONParser(919): at java.lang.Thread.run(Thread.java:856)
03-19 12:45:12.985: D/JSONParser(919): Parse JSON
03-19 12:45:31.570: D/JSONParser(919): JSONException:
03-19 12:45:31.570: D/JSONParser(919): org.json.JSONException: End of input at character 0 of
03-19 12:45:31.570: D/JSONParser(919): at org.json.JSONTokener.syntaxError(JSONTokener.java:450)
03-19 12:45:31.570: D/JSONParser(919): at org.json.JSONTokener.nextValue(JSONTokener.java:97)
03-19 12:45:31.570: D/JSONParser(919): at org.json.JSONObject.<init>(JSONObject.java:154)
03-19 12:45:31.570: D/JSONParser(919): at org.json.JSONObject.<init>(JSONObject.java:171)
03-19 12:45:31.570: D/JSONParser(919): at com.spyraa.bookstore.JSONParser.makeHttpRequest(JSONParser.java:101)
03-19 12:45:31.570: D/JSONParser(919): at com.spyraa.bookstore.Latest$LoadAllProducts.doInBackground(Latest.java:105)
03-19 12:45:31.570: D/JSONParser(919): at com.spyraa.bookstore.Latest$LoadAllProducts.doInBackground(Latest.java:1)
03-19 12:45:31.570: D/JSONParser(919): at android.os.AsyncTask$2.call(AsyncTask.java:287)
03-19 12:45:31.570: D/JSONParser(919): at java.util.concurrent.FutureTask.run(FutureTask.java:234)
03-19 12:45:31.570: D/JSONParser(919): at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1080)
03-19 12:45:31.570: D/JSONParser(919): at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:573)
03-19 12:45:31.570: D/JSONParser(919): at java.lang.Thread.run(Thread.java:856)
03-19 12:45:32.365: D/dalvikvm(919): GC_CONCURRENT freed 412K, 17% free 2798K/3352K, paused 55ms+31ms, total 671ms
除了上述内容之外，大多数logcat都包含以下内容：
03-19 12:45:44.466: I/Choreographer(919): Skipped 289 frames! The application may be doing too much work on its main thread.
03-19 12:45:44.706: W/Trace(919): Unexpected value from nativeGetEnabledTags: 0
答案 0 :(得分：1)
由于您没有提供行号，我可以猜测。
解析数据时出错org.json.JSONException：
的字符0处的输入结束
提示无效的JSON字符串。您应该将收到的JSON字符串打印到logcat以进行调试。
<强>更新：
JSONParser的问题（我到目前为止看到的）主要是它捕获异常，转储一些消息然后继续。结果是你通常有几条消息，并且不知道它最初失败的地方。
这就是您必须将跟踪语句添加到makeHttpRequest()以查看其失败的原因。另一种（附加）方法是删除所有try / catch语句，并将异常传播到外部。然后，您将看到第一个故障所在的堆栈跟踪，并且可以查看问题的真正原因。
但即便如此，正确的跟踪和调试日志也是必不可少的。
答案 1 :(得分：0)
听起来像是处理不当的JSON数据。你确定你得到的JSON的结构？一个样本可能有所帮助。
答案 2 :(得分：0)
尝试使用对象而不是原始数据类型。原始类型（int，float，double等）不能存储空值。
int替换为Integer
Integer success = json.getInt(TAG_SUCCESS);