如何在 Java/Android 中处理慢速网络连接 [英] How to handle slow network connection in Java/Android
问题描述
我有一个应用程序，它对 MySQL 数据库进行了多次调用；它在 AsyncTask 中执行此操作.下面是一个示例.
I have an app that uses many, many calls to a MySQL database; it does this inside an AsyncTask. Below is a sample of what one may look like.
我的主要问题是这个；有时，主机(Godaddy，呃)决定停止连接，我的 progressDialog 加载，加载，加载更多，直到强制关闭并且应用程序崩溃.特别是如果用户试图中断它(但是，我已将大多数设置为不可取消).
My main question is this; sometimes, the host (Godaddy, ugh) decides to stall a connection and my progressDialog loads, and loads, and loads some more, until there is a force close and the app crashes. Especially if the user tries to interrupt it (most I have set to non-cancelable, however).
有没有比我下面更好的方法来处理这个问题?我是在 try/catch 中做的，但不知道如何利用它对我有利.
Is there a better way to handle this than I am below? I am doing it in a try/catch, but not sure how to use that to my advantage.
class Task extends AsyncTask<String, String, Void> {
private ProgressDialog progressDialog = new ProgressDialog(
MasterCat.this);
InputStream is = null;
String result = "";
protected void onPreExecute() {
progressDialog.setMessage("Loading...");
progressDialog.show();
progressDialog.setCancelable(false);
}
@Override
protected Void doInBackground(String... params) {
String url_select = "http://www.---.com/---/master.php";
HttpClient httpClient = new DefaultHttpClient();
HttpPost httpPost = new HttpPost(url_select);
ArrayList<NameValuePair> param = new ArrayList<NameValuePair>();
try {
httpPost.setEntity(new UrlEncodedFormEntity(param));
HttpResponse httpResponse = httpClient.execute(httpPost);
HttpEntity httpEntity = httpResponse.getEntity();
// read content
is = httpEntity.getContent();
} catch (Exception e) {
Log.e("log_tag", "Error in http connection " + e.toString());
}
try {
BufferedReader br = new BufferedReader(
new InputStreamReader(is));
StringBuilder sb = new StringBuilder();
String line = "";
while ((line = br.readLine()) != null) {
sb.append(line + "
");
}
is.close();
result = sb.toString();
} catch (Exception e) {
// TODO: handle exception
Log.e("log_tag", "Error converting result " + e.toString());
}
return null;
}
protected void onPostExecute(Void v) {
String cat;
try {
jArray = new JSONArray(result);
JSONObject json_data = null;
for (int i = 0; i < jArray.length(); i++) {
json_data = jArray.getJSONObject(i);
cat = json_data.getString("category");
cats.add(cat);
}
} catch (JSONException e1) {
Toast.makeText(getBaseContext(), "No Categories Found",
Toast.LENGTH_LONG).show();
} catch (ParseException e1) {
e1.printStackTrace();
}
ListView listView = getListView();
listView.setTextFilterEnabled(true);
listView.setOnItemClickListener(new OnItemClickListener() {
public void onItemClick(AdapterView<?> arg0, View arg1,
int arg2, long id) {
Intent i = new Intent(getApplicationContext(), Items.class);
i.putExtra("category", cats.get(arg2));
startActivity(i);
}
});
progressDialog.dismiss();
MasterCatAdapter adapter = new MasterCatAdapter(MasterCat.this,
cats);
setListAdapter(adapter);
}
}
现在我假设强制关闭是因为连接不良；但是当我可以重新创建它时，我会尝试启动它.
Now I AM assuming the force close is because of the poor connection; but I will try to get alogcat up when I can recreate it.
Edit2:这是 LogCat:
here is LogCat:
08-13 14:57:00.580: E/WindowManager(2262): Activity com.---.---.MyFragmentActivity has leaked window com.android.internal.policy.impl.PhoneWindow$DecorView@42b02cd0 that was originally added here
08-13 14:57:00.580: E/WindowManager(2262): android.view.WindowLeaked: Activity com.---.---.MyFragmentActivity has leaked window com.android.internal.policy.impl.PhoneWindow$DecorView@42b02cd0 that was originally added here
08-13 14:57:00.580: E/WindowManager(2262): at android.view.ViewRootImpl.<init>(ViewRootImpl.java:374)
08-13 14:57:00.580: E/WindowManager(2262): at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:292)
08-13 14:57:00.580: E/WindowManager(2262): at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:224)
08-13 14:57:00.580: E/WindowManager(2262): at android.view.WindowManagerImpl$CompatModeWrapper.addView(WindowManagerImpl.java:149)
08-13 14:57:00.580: E/WindowManager(2262): at android.view.Window$LocalWindowManager.addView(Window.java:547)
08-13 14:57:00.580: E/WindowManager(2262): at android.app.Dialog.show(Dialog.java:277)
08-13 14:57:00.580: E/WindowManager(2262): at com.---.---.MyFragmentActivity$RateFragment$RatingTask.onPreExecute(MyFragmentActivity.java:374)
08-13 14:57:00.580: E/WindowManager(2262): at android.os.AsyncTask.executeOnExecutor(AsyncTask.java:586)
08-13 14:57:00.580: E/WindowManager(2262): at android.os.AsyncTask.execute(AsyncTask.java:534)
08-13 14:57:00.580: E/WindowManager(2262): at com.---.---.MyFragmentActivity$RateFragment$insertTask.onPostExecute(MyFragmentActivity.java:520)
08-13 14:57:00.580: E/WindowManager(2262): at com.---.---.MyFragmentActivity$RateFragment$insertTask.onPostExecute(MyFragmentActivity.java:1)
08-13 14:57:00.580: E/WindowManager(2262): at android.os.AsyncTask.finish(AsyncTask.java:631)
08-13 14:57:00.580: E/WindowManager(2262): at android.os.AsyncTask.access$600(AsyncTask.java:177)
08-13 14:57:00.580: E/WindowManager(2262): at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:644)
08-13 14:57:00.580: E/WindowManager(2262): at android.os.Handler.dispatchMessage(Handler.java:99)
08-13 14:57:00.580: E/WindowManager(2262): at android.os.Looper.loop(Looper.java:137)
08-13 14:57:00.580: E/WindowManager(2262): at android.app.ActivityThread.main(ActivityThread.java:4745)
08-13 14:57:00.580: E/WindowManager(2262): at java.lang.reflect.Method.invokeNative(Native Method)
08-13 14:57:00.580: E/WindowManager(2262): at java.lang.reflect.Method.invoke(Method.java:511)
08-13 14:57:00.580: E/WindowManager(2262): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
08-13 14:57:00.580: E/WindowManager(2262): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
08-13 14:57:00.580: E/WindowManager(2262): at dalvik.system.NativeStart.main(Native Method)
08-13 14:57:00.588: D/AndroidRuntime(2262): Shutting down VM
08-13 14:57:00.588: W/dalvikvm(2262): threadid=1: thread exiting with uncaught exception (group=0x4200b300)
08-13 14:57:00.596: E/AndroidRuntime(2262): FATAL EXCEPTION: main
08-13 14:57:00.596: E/AndroidRuntime(2262): java.lang.NullPointerException
08-13 14:57:00.596: E/AndroidRuntime(2262): at com.---.---.MyFragmentActivity$RateFragment$RatingTask.onPostExecute(MyFragmentActivity.java:461)
08-13 14:57:00.596: E/AndroidRuntime(2262): at com.---.---.MyFragmentActivity$RateFragment$RatingTask.onPostExecute(MyFragmentActivity.java:1)
08-13 14:57:00.596: E/AndroidRuntime(2262): at android.os.AsyncTask.finish(AsyncTask.java:631)
08-13 14:57:00.596: E/AndroidRuntime(2262): at android.os.AsyncTask.access$600(AsyncTask.java:177)
08-13 14:57:00.596: E/AndroidRuntime(2262): at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:644)
08-13 14:57:00.596: E/AndroidRuntime(2262): at android.os.Handler.dispatchMessage(Handler.java:99)
08-13 14:57:00.596: E/AndroidRuntime(2262): at android.os.Looper.loop(Looper.java:137)
08-13 14:57:00.596: E/AndroidRuntime(2262): at android.app.ActivityThread.main(ActivityThread.java:4745)
08-13 14:57:00.596: E/AndroidRuntime(2262): at java.lang.reflect.Method.invokeNative(Native Method)
08-13 14:57:00.596: E/AndroidRuntime(2262): at java.lang.reflect.Method.invoke(Method.java:511)
08-13 14:57:00.596: E/AndroidRuntime(2262): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
08-13 14:57:00.596: E/AndroidRuntime(2262): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
08-13 14:57:00.596: E/AndroidRuntime(2262): at dalvik.system.NativeStart.main(Native Method)
这是在不同活动中但在 LogCat 中被引用的任务:
Here is the Task that is in a different activity but being referenced in LogCat:
class RatingTask extends AsyncTask<String, String, Void> {
private ProgressDialog progressDialog = new ProgressDialog(
getActivity());
InputStream is = null;
String result = "";
protected void onPreExecute() {
progressDialog.setMessage("Loading...");
progressDialog.show();
progressDialog.setOnCancelListener(new OnCancelListener() {
public void onCancel(DialogInterface dialog) {
RatingTask.this.cancel(true);
}
});
}
@Override
protected Void doInBackground(String... params) {
String url_select = "http://www.---.com/---/get_ratings.php";
ArrayList<NameValuePair> param = new ArrayList<NameValuePair>();
param.add(new BasicNameValuePair("item", Item));
param.add(new BasicNameValuePair("category", Category));
HttpClient httpClient = new DefaultHttpClient();
HttpPost httpPost = new HttpPost(url_select);
try {
httpPost.setEntity(new UrlEncodedFormEntity(param));
HttpResponse httpResponse = httpClient.execute(httpPost);
HttpEntity httpEntity = httpResponse.getEntity();
// read content
is = httpEntity.getContent();
} catch (Exception e) {
Log.e("log_tag", "Error in http connection " + e.toString());
}
try {
BufferedReader br = new BufferedReader(
new InputStreamReader(is));
StringBuilder sb = new StringBuilder();
String line = "";
while ((line = br.readLine()) != null) {
sb.append(line + "
");
}
is.close();
result = sb.toString();
} catch (Exception e) {
Log.e("log_tag", "Error converting result " + e.toString());
}
return null;
}
protected void onPostExecute(Void v) {
String starTotal = null, starAvg = null;
try {
JSONArray jArray = new JSONArray(result);
JSONObject json_data = null;
for (int i = 0; i < jArray.length(); i++) {
json_data = jArray.getJSONObject(i);
starTotal = json_data.getString("TotalRating");
starAvg = json_data.getString("AverageRating");
}
} catch (JSONException e1) {
Log.e("log_tag",
"Error in http connection " + e1.toString());
Toast.makeText(getActivity(), "JSONexception",
Toast.LENGTH_LONG).show();
} catch (ParseException e1) {
e1.printStackTrace();
}
int total = 0;
if (starTotal != null) {
total = Integer.parseInt(starTotal);
} else {
starTotal = "0";
}
if (total > 0) {
total = Integer.parseInt(starTotal);
} else {
total = 0;
}
StarTotal = (TextView) getActivity().findViewById(
R.id.tvStarTotal);
StarTotal.setText("(" + String.valueOf(total) + (")"));
float avg = 0.f;
try {
avg = Float.parseFloat(starAvg);
} catch (NumberFormatException e) {
avg = 0;
}
DecimalFormat myFormat = new DecimalFormat("0.00");
StarNumbers = (TextView) getActivity().findViewById(
R.id.tvStarNumber);
StarNumbers.setText(myFormat.format(avg));
ratingsBarTwo.setRating(Float.valueOf(avg));
progressDialog.dismiss();
}
}
推荐答案
首先检查是否有可用的连接，如果没有则通知用户.
Begin with checking if there is a connection available, and notify the user if there isn't.
特别是如果用户试图打断它(不过，我已将大多数设置为不可取消).
Especially if the user tries to interrupt it (most I have set to non-cancelable, however).
我会重新考虑这个决定.就个人而言，我不喜欢不可中断的进程.我的建议是，您按照@CommonsWare 在此处的评论中的建议继续操作.很快，有一个布尔变量来检查数据是否无效，或者你自己检查你的数据是否为空.如果是，请不要执行基于此数据的任何命令，您将不会有任何与此相关的强制关闭.
I would reconsider that decision. Personally, I don't like non-interruptible processes. My suggestion is that you go on from what @CommonsWare suggests in the comments here. Shortly, have a boolean variable that checks whether the data is invalid or your own check to see if your data is null. If it is, don't execute any commands based from this data and you won't have any force closes related to this.
有没有比我下面更好的方法来处理这个问题?
Is there a better way to handle this than I am below?
除了上述内容之外，我还建议向您的 http 客户端添加一些 HTTP 参数.例如:
Besides from what is stated above, I'd recommend adding some HTTP parameters to your http client. For example:
final int CONN_WAIT_TIME = 3000;
final int CONN_DATA_WAIT_TIME = 2000;
HttpParams httpParams = new BasicHttpParams();
HttpConnectionParams.setConnectionTimeout(httpParams, CONN_WAIT_TIME);
HttpConnectionParams.setSoTimeout(httpParams, CONN_DATA_WAIT_TIME);
DefaultHttpClient postClient = new DefaultHttpClient(httpParams);
// Go on...
如果您的 http 客户端超过了您在各自字段中输入的时间，它只会给您一个 ConnectTimeoutException.现在您已经足够了解 onPostExecute() 中的数据是否有效以及是否应该继续使用它.
If your http client exceeds the time you put in their respective fields, it will simply give you a ConnectTimeoutException. Now you know enough to consider if the data is valid in onPostExecute() and whether you should go on using it or not.
这篇关于如何在 Java/Android 中处理慢速网络连接的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
