Android URL 连接和线程问题，以及 IllegalStateExceptions
Android problems with URL connection and threading, and IllegalStateExceptions
这是 class，应该允许我连接到 url 并从中检索数据。它将 JSON 数据转换为字符串。也许这里有问题，我看不到。我对这种编程还很陌生。
public class NetworkConnection extends AsyncTask<String, Void, String> {
private static final String DEBUG_TAG = "HttpExample";
protected String doInBackground(String... urls) {
try{
return downloadUrl(urls[0]);
} catch (IOException e) {
return "Unable to retrieve Web Page";
}
}
//Fetch the data from the URL
public String downloadUrl(String myurl) throws IOException {
InputStream is = null;
int len = 500;
String text = new String();
try {
URL url = new URL(myurl);
HttpURLConnection conn = (HttpURLConnection) url.openConnection();
conn.setReadTimeout(10000 /* milliseconds */);
conn.setConnectTimeout(15000 /* milliseconds */);
conn.setRequestMethod("GET");
conn.setDoInput(true);
// Starts the query
conn.connect();
int response = conn.getResponseCode();
Log.d(DEBUG_TAG, "The response is: " + response);
is = conn.getInputStream();
try {
BufferedReader br = new BufferedReader(
new InputStreamReader(
conn.getInputStream()));
StringBuilder sb = new StringBuilder();
String line;
while ((line = br.readLine()) != null) {
sb.append(line + "\n");
}
br.close();
JSONArray data = new JSONArray(sb.toString());
for (int i = 0; i < data.length(); i++) {
JSONObject row = data.getJSONObject(i);
String klasse = row.getString("K_Nr");
String raum = row.getString("K_Raum");
text = text + klasse + ": " + raum + "\n";
}
} catch (IOException e) {
} catch (JSONException e) {
e.printStackTrace();
}
} finally {
if (is != null) {
is.close();
}
}
return text;
}
@Override
protected void onPostExecute(String s){
super.onPostExecute(s);
}
}
这是主线程UI所在的class。在这里，我尝试通过 class 网络连接访问 url。问题是我不知道如何正确穿线。
public class Start extends Activity {
// public String URL = new String("http://10.0.2.2/?action=getKlassen");
// public String URL = new String("http://127.0.0.1/webservice/ajax.php?action=getKlassen");
public String URL;
NetworkConnection netCon;
public TextView testAusgabe;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
Intent i = getIntent();
String val = i.getStringExtra("Klasse");
TextView ausgabe = (TextView) findViewById(R.id.ausgabe);
testAusgabe = (TextView)findViewById(R.id.testAusgabe);
netCon = new NetworkConnection();
URL = new String("http://10.0.2.2/?action=getKlassen");
ausgabe.setText(val);
}
public void myClickHandler(View view) {
ConnectivityManager connMgr = (ConnectivityManager)
getSystemService(Context.CONNECTIVITY_SERVICE);
NetworkInfo networkInfo = connMgr.getActiveNetworkInfo();
if (networkInfo != null && networkInfo.isConnected()) {
new NetworkConnection().execute(URL);
} else {
testAusgabe.setText("No network connection available.");
}
}
public void onClick(View view){
}
public void zeigeListe_Click (View view) {
startActivity(new Intent(this, KlassenView.class));
}
public void ladeDaten_Click(View view) {
String data;
data = netCon.doInBackground(URL);
testAusgabe.setText(data);
}
}
这里我们有抛出的异常。当我单击应该加载数据的按钮时，应用程序崩溃了。它肯定有线程问题，但我不明白其他例外情况。如果有人可以提供帮助，那就太好了。提前致谢。
01-29 11:10:38.776 6648-6648/com.example.httptest E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.httptest, PID: 6648
java.lang.IllegalStateException: Could not execute method for android:onClick
at android.view.View$DeclaredOnClickListener.onClick(View.java:4452)
at android.view.View.performClick(View.java:5198)
at android.view.View$PerformClick.run(View.java:21147)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
Caused by: java.lang.reflect.InvocationTargetException
at java.lang.reflect.Method.invoke(Native Method)
at android.view.View$DeclaredOnClickListener.onClick(View.java:4447)
at android.view.View.performClick(View.java:5198)
at android.view.View$PerformClick.run(View.java:21147)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
Caused by: android.os.NetworkOnMainThreadException
at android.os.StrictMode$AndroidBlockGuardPolicy.onNetwork(StrictMode.java:1273)
at libcore.io.BlockGuardOs.connect(BlockGuardOs.java:110)
at libcore.io.IoBridge.connectErrno(IoBridge.java:154)
at libcore.io.IoBridge.connect(IoBridge.java:122)
at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:183)
at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:452)
at java.net.Socket.connect(Socket.java:884)
at com.android.okhttp.internal.Platform.connectSocket(Platform.java:117)
at com.android.okhttp.internal.http.SocketConnector.connectRawSocket(SocketConnector.java:160)
at com.android.okhttp.internal.http.SocketConnector.connectCleartext(SocketConnector.java:67)
at com.android.okhttp.Connection.connect(Connection.java:152)
at com.android.okhttp.Connection.connectAndSetOwner(Connection.java:185)
at com.android.okhttp.OkHttpClient.connectAndSetOwner(OkHttpClient.java:128)
at com.android.okhttp.internal.http.HttpEngine.nextConnection(HttpEngine.java:341)
at com.android.okhttp.internal.http.HttpEngine.connect(HttpEngine.java:330)
at com.android.okhttp.internal.http.HttpEngine.sendRequest(HttpEngine.java:248)
at com.android.okhttp.internal.huc.HttpURLConnectionImpl.execute(HttpURLConnectionImpl.java:433)
at com.android.okhttp.internal.huc.HttpURLConnectionImpl.connect(HttpURLConnectionImpl.java:114)
at com.example.httptest.NetworkConnection.downloadUrl(NetworkConnection.java:50)
at com.example.httptest.NetworkConnection.doInBackground(NetworkConnection.java:29)
at com.example.httptest.Start.ladeDaten_Click(Start.java:62)
at java.lang.reflect.Method.invoke(Native Method)
at android.view.View$DeclaredOnClickListener.onClick(View.java:4447)
at android.view.View.performClick(View.java:5198)
at android.view.View$PerformClick.run(View.java:21147)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
您可以在 LogCat 中看到您有一个 NetworkOnMainThreadException。
如果您试图在主线程中执行网络代码，就会出现这种异常。
对此类代码使用 AsyncTask 或线程。
其实！你在你的代码中犯了一个错误。
你必须使用
netCon.execute(URL);代替
netCon.doInBackground(URL);
一旦调用了 execute() 方法，并且在完成之前的 doInBackground() 之前再次单击以启动该方法，则会再次发生异常。
所以做一件事：
在方法 onPreExecute() 中，防止您的按钮再次被点击，在 onPostExecute() 中，使其再次可点击。
因此，通过这种方式您可以防止创建新线程。
干杯!
这是 class，应该允许我连接到 url 并从中检索数据。它将 JSON 数据转换为字符串。也许这里有问题，我看不到。我对这种编程还很陌生。
public class NetworkConnection extends AsyncTask<String, Void, String> {
private static final String DEBUG_TAG = "HttpExample";
protected String doInBackground(String... urls) {
try{
return downloadUrl(urls[0]);
} catch (IOException e) {
return "Unable to retrieve Web Page";
}
}
//Fetch the data from the URL
public String downloadUrl(String myurl) throws IOException {
InputStream is = null;
int len = 500;
String text = new String();
try {
URL url = new URL(myurl);
HttpURLConnection conn = (HttpURLConnection) url.openConnection();
conn.setReadTimeout(10000 /* milliseconds */);
conn.setConnectTimeout(15000 /* milliseconds */);
conn.setRequestMethod("GET");
conn.setDoInput(true);
// Starts the query
conn.connect();
int response = conn.getResponseCode();
Log.d(DEBUG_TAG, "The response is: " + response);
is = conn.getInputStream();
try {
BufferedReader br = new BufferedReader(
new InputStreamReader(
conn.getInputStream()));
StringBuilder sb = new StringBuilder();
String line;
while ((line = br.readLine()) != null) {
sb.append(line + "\n");
}
br.close();
JSONArray data = new JSONArray(sb.toString());
for (int i = 0; i < data.length(); i++) {
JSONObject row = data.getJSONObject(i);
String klasse = row.getString("K_Nr");
String raum = row.getString("K_Raum");
text = text + klasse + ": " + raum + "\n";
}
} catch (IOException e) {
} catch (JSONException e) {
e.printStackTrace();
}
} finally {
if (is != null) {
is.close();
}
}
return text;
}
@Override
protected void onPostExecute(String s){
super.onPostExecute(s);
}
}
这是主线程UI所在的class。在这里，我尝试通过 class 网络连接访问 url。问题是我不知道如何正确穿线。
public class Start extends Activity {
// public String URL = new String("http://10.0.2.2/?action=getKlassen");
// public String URL = new String("http://127.0.0.1/webservice/ajax.php?action=getKlassen");
public String URL;
NetworkConnection netCon;
public TextView testAusgabe;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
Intent i = getIntent();
String val = i.getStringExtra("Klasse");
TextView ausgabe = (TextView) findViewById(R.id.ausgabe);
testAusgabe = (TextView)findViewById(R.id.testAusgabe);
netCon = new NetworkConnection();
URL = new String("http://10.0.2.2/?action=getKlassen");
ausgabe.setText(val);
}
public void myClickHandler(View view) {
ConnectivityManager connMgr = (ConnectivityManager)
getSystemService(Context.CONNECTIVITY_SERVICE);
NetworkInfo networkInfo = connMgr.getActiveNetworkInfo();
if (networkInfo != null && networkInfo.isConnected()) {
new NetworkConnection().execute(URL);
} else {
testAusgabe.setText("No network connection available.");
}
}
public void onClick(View view){
}
public void zeigeListe_Click (View view) {
startActivity(new Intent(this, KlassenView.class));
}
public void ladeDaten_Click(View view) {
String data;
data = netCon.doInBackground(URL);
testAusgabe.setText(data);
}
}
这里我们有抛出的异常。当我单击应该加载数据的按钮时，应用程序崩溃了。它肯定有线程问题，但我不明白其他例外情况。如果有人可以提供帮助，那就太好了。提前致谢。
01-29 11:10:38.776 6648-6648/com.example.httptest E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.httptest, PID: 6648
java.lang.IllegalStateException: Could not execute method for android:onClick
at android.view.View$DeclaredOnClickListener.onClick(View.java:4452)
at android.view.View.performClick(View.java:5198)
at android.view.View$PerformClick.run(View.java:21147)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
Caused by: java.lang.reflect.InvocationTargetException
at java.lang.reflect.Method.invoke(Native Method)
at android.view.View$DeclaredOnClickListener.onClick(View.java:4447)
at android.view.View.performClick(View.java:5198)
at android.view.View$PerformClick.run(View.java:21147)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
Caused by: android.os.NetworkOnMainThreadException
at android.os.StrictMode$AndroidBlockGuardPolicy.onNetwork(StrictMode.java:1273)
at libcore.io.BlockGuardOs.connect(BlockGuardOs.java:110)
at libcore.io.IoBridge.connectErrno(IoBridge.java:154)
at libcore.io.IoBridge.connect(IoBridge.java:122)
at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:183)
at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:452)
at java.net.Socket.connect(Socket.java:884)
at com.android.okhttp.internal.Platform.connectSocket(Platform.java:117)
at com.android.okhttp.internal.http.SocketConnector.connectRawSocket(SocketConnector.java:160)
at com.android.okhttp.internal.http.SocketConnector.connectCleartext(SocketConnector.java:67)
at com.android.okhttp.Connection.connect(Connection.java:152)
at com.android.okhttp.Connection.connectAndSetOwner(Connection.java:185)
at com.android.okhttp.OkHttpClient.connectAndSetOwner(OkHttpClient.java:128)
at com.android.okhttp.internal.http.HttpEngine.nextConnection(HttpEngine.java:341)
at com.android.okhttp.internal.http.HttpEngine.connect(HttpEngine.java:330)
at com.android.okhttp.internal.http.HttpEngine.sendRequest(HttpEngine.java:248)
at com.android.okhttp.internal.huc.HttpURLConnectionImpl.execute(HttpURLConnectionImpl.java:433)
at com.android.okhttp.internal.huc.HttpURLConnectionImpl.connect(HttpURLConnectionImpl.java:114)
at com.example.httptest.NetworkConnection.downloadUrl(NetworkConnection.java:50)
at com.example.httptest.NetworkConnection.doInBackground(NetworkConnection.java:29)
at com.example.httptest.Start.ladeDaten_Click(Start.java:62)
at java.lang.reflect.Method.invoke(Native Method)
at android.view.View$DeclaredOnClickListener.onClick(View.java:4447)
at android.view.View.performClick(View.java:5198)
at android.view.View$PerformClick.run(View.java:21147)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
您可以在 LogCat 中看到您有一个 NetworkOnMainThreadException。
如果您试图在主线程中执行网络代码，就会出现这种异常。
对此类代码使用 AsyncTask 或线程。
其实！你在你的代码中犯了一个错误。
你必须使用
netCon.execute(URL);代替
netCon.doInBackground(URL);
一旦调用了 execute() 方法，并且在完成之前的 doInBackground() 之前再次单击以启动该方法，则会再次发生异常。
所以做一件事：
在方法 onPreExecute() 中，防止您的按钮再次被点击，在 onPostExecute() 中，使其再次可点击。
因此，通过这种方式您可以防止创建新线程。 干杯!