我正在尝试实现异步任务以满足android中的json函数。 json函数在android 2.3.3中完全正常工作。所以现在我需要将它实现到android中。 4.3果冻豆平台。但它无法像我预期的那样显示任何结果。 Async Task功能出了问题。请帮帮....
public class Update extends Activity{
JSONArray jArray = null;
String result = null;
StringBuilder sb = null;
InputStream is = null;
String ct_name;
LinearLayout l;
@Override
protected void onCreate(Bundle savedInstanceState){
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_update);
Toast.makeText(getBaseContext(), "Done layout",Toast.LENGTH_LONG).show();
class LongOperation extends AsyncTask<String, Void, String>{
@Override
protected String doInBackground(String... params) {
ArrayList<NameValuePair> nameValuePairs = new ArrayList<NameValuePair>();
//http post
try{
HttpClient httpclient = new DefaultHttpClient();
//Why to use 10.0.2.2
HttpPost httppost = new HttpPost("http://10.0.2.2/moodle/myFile.php");
httppost.setEntity(new UrlEncodedFormEntity(nameValuePairs));
HttpResponse response = httpclient.execute(httppost);
HttpEntity entity = response.getEntity();
is = entity.getContent();
}catch(Exception e){
Log.e("log_tag", "Error in http connection"+e.toString());
}
//convert response to string
try{
BufferedReader reader = new BufferedReader(new InputStreamReader(is,"iso-8859-1"),8);
sb = new StringBuilder();
sb.append(reader.readLine() + "\n");
String line="0";
while ((line = reader.readLine()) != null) {
sb.append(line + "\n");
}
is.close();
result=sb.toString();
}catch(Exception e){
Log.e("log_tag", "Error converting result "+e.toString());
}
try{
jArray = new JSONArray(result);
JSONObject json_data=null;
l = (LinearLayout) findViewById(R.id.container);
for(int i=0;i<jArray.length();i++){
json_data = jArray.getJSONObject(i);
ct_name=json_data.getString("name");//here "Name" is the column name in database
}
}
catch(JSONException e1){
Toast.makeText(getBaseContext(), "No Data Found" ,Toast.LENGTH_LONG).show();
} catch (ParseException e1) {
e1.printStackTrace();
}
return result;
}
protected void onPostExecute(String result) {
TextView txt = (TextView) findViewById(R.id.txt_1);
txt.setText("Executed");
Toast.makeText(getBaseContext(), "this is post",Toast.LENGTH_LONG).show();
Toast.makeText(getBaseContext(), ct_name,
Toast.LENGTH_LONG).show();
TextView textView = new TextView(null);
textView.setText(ct_name + " is out, please attempt it as soon as possible"+ "\n");
l.addView(textView);
}
}
Toast.makeText(getBaseContext(), "lol",
Toast.LENGTH_LONG).show();
}
}
/////////////////////////////////////////////// //////////////////////////////////////////// 可行的json代码
公共类MainActivity扩展了Activity {
JSONArray jArray = null;
String result = null;
StringBuilder sb = null;
InputStream is = null;
String ct_name;
LinearLayout l;
@Override
protected void onCreate(Bundle savedInstanceState){
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
ArrayList<NameValuePair> nameValuePairs = new ArrayList<NameValuePair>();
//http post
try{
HttpClient httpclient = new DefaultHttpClient();
//Why to use 10.0.2.2
HttpPost httppost = new HttpPost("http://10.0.2.2/moodle/myFile.php");
httppost.setEntity(new UrlEncodedFormEntity(nameValuePairs));
HttpResponse response = httpclient.execute(httppost);
HttpEntity entity = response.getEntity();
is = entity.getContent();
}catch(Exception e){
Log.e("log_tag", "Error in http connection"+e.toString());
}
//convert response to string
try{
BufferedReader reader = new BufferedReader(new InputStreamReader(is,"iso-8859-1"),8);
sb = new StringBuilder();
sb.append(reader.readLine() + "\n");
String line="0";
while ((line = reader.readLine()) != null) {
sb.append(line + "\n");
}
is.close();
result=sb.toString();
}catch(Exception e){
Log.e("log_tag", "Error converting result "+e.toString());
}
try{
jArray = new JSONArray(result);
JSONObject json_data=null;
l = (LinearLayout) findViewById(R.id.container);
for(int i=0;i<jArray.length();i++){
json_data = jArray.getJSONObject(i);
ct_name=json_data.getString("name");//here "Name" is the column name in database
Toast.makeText(getBaseContext(), ct_name,
Toast.LENGTH_LONG).show();
TextView textView = new TextView(this);
textView.setText(ct_name + " is out, please attempt it as soon as possible"+ "\n");
l.addView(textView);
}
}
catch(JSONException e1){
Toast.makeText(getBaseContext(), "No Data Found" ,Toast.LENGTH_LONG).show();
} catch (ParseException e1) {
e1.printStackTrace();
}
}
}
答案 0 :(得分：0)
您正试图在doInBackground(String... params)中做一些无法做到的事情。使用Assync时，仅在onPreExecute或onPostExecute中更新UI中的任何内容。在这个你试图吐司并附上最终会崩溃的视图。如果你真的想要从后台更新UI，即使它不是一个很好的appoch来解决问题，你可以使用runOnUiThread(action)。使用Assync任务时请记住这一点。无法从后台更新UI。
答案 1 :(得分：0)
它正在崩溃，因为你在doInBackGround（）catch部分中显示toast。您无法从不同的线程更新UI。
答案 2 :(得分：0)
用以下代码替换您的代码：
public class Update extends Activity {
JSONArray jArray = null;
String result = null;
StringBuilder sb = null;
InputStream is = null;
String ct_name;
LinearLayout l;
String responseString;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_update);
Toast.makeText(getBaseContext(), "Done layout", Toast.LENGTH_LONG)
.show();
new LongOperation().execute();
}
class LongOperation extends AsyncTask<String, String, String> {
@Override
protected String doInBackground(String... params) {
// http post
HttpClient httpclient = new DefaultHttpClient();
// Why to use 10.0.2.2
HttpPost httppost = new HttpPost(
"http://10.0.2.2/moodle/myFile.php");
try {
ArrayList<NameValuePair> nameValuePairs = new ArrayList<NameValuePair>();
httppost.setEntity(new UrlEncodedFormEntity(nameValuePairs));
HttpResponse response = httpclient.execute(httppost);
response.getStatusLine().getStatusCode();
HttpEntity getResponseEntity = response.getEntity();
responseString = EntityUtils.toString(getResponseEntity);
} catch (ClientProtocolException e) {
// TODO Auto-generated catch block
} catch (IOException e) {
// TODO Auto-generated catch block
}
return responseString;
}
protected void onPostExecute(String resultStr) {
try {
JSONObject json = new JSONObject(responseString);
JSONArray jArray = json.getJSONArray("result");
l = (LinearLayout) findViewById(R.id.container);
for (int i = 0; i < jArray.length(); i++) {
JSONObject json_data = jArray.getJSONObject(i);
ct_name = json_data.getString("name");
}
TextView txt = (TextView) findViewById(R.id.txt_1);
txt.setText("Executed");
Toast.makeText(getBaseContext(), "this is post",
Toast.LENGTH_LONG).show();
Toast.makeText(getBaseContext(), ct_name, Toast.LENGTH_LONG)
.show();
TextView textView = new TextView(null);
textView.setText(ct_name
+ " is out, please attempt it as soon as possible"
+ "\n");
l.addView(textView);
} catch (JSONException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
}
答案 3 :(得分：0)
但它无法显示我预期的任何结果
您似乎不会首先调用异步任务。添加以下内容：
new LongOperation().execute();
同时至少将e.printStackTrace()添加到您的catch块中，以便发现更多问题。