我正在尝试创建一个Android应用程序。我希望通过REST API服务将我的Android应用程序连接到Web应用程序。所有内容都与WEB端正确相关。我也尝试使用TableLayout它可以正常工作，但我没有＆＃39;我想使用TableLayout，我想使用RelativeLayout。当用户点击下载按钮时，JSON数据应该来自网络端。随着布局，当点击下载按钮时，＃34; retrieveSampleData＆＃34;应该调用方法然后AsyncTask.But它给我以下日志记录：
03-15 17:06:31.730: E/AndroidRuntime(2012): FATAL EXCEPTION: main
03-15 17:06:31.730: E/AndroidRuntime(2012): java.lang.IllegalStateException: Could not
execute method of the activity
03-15 17:06:31.730: E/AndroidRuntime(2012): at android.view.View$1.onClick(View.java:3633)
03-15 17:06:31.730: E/AndroidRuntime(2012): at android.view.View.performClick(View.java:4240)
03-15 17:06:31.730: E/AndroidRuntime(2012): at
android.view.View$PerformClick.run(View.java:17721)
03-15 17:06:31.730: E/AndroidRuntime(2012): at
android.os.Handler.handleCallback(Handler.java:730)
03-15 17:06:31.730: E/AndroidRuntime(2012): at
android.os.Handler.dispatchMessage(Handler.java:92)
03-15 17:06:31.730: E/AndroidRuntime(2012): at android.os.Looper.loop(Looper.java:137)
03-15 17:06:31.730: E/AndroidRuntime(2012): at
android.app.ActivityThread.main(ActivityThread.java:5103)
03-15 17:06:31.730: E/AndroidRuntime(2012): at java.lang.reflect.Method.invokeNative(Native
Method)
03-15 17:06:31.730: E/AndroidRuntime(2012): at java.lang.reflect.Method.invoke(Method.java:525)
03-15 17:06:31.730: E/AndroidRuntime(2012): at
com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
03-15 17:06:31.730: E/AndroidRuntime(2012): at
com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
03-15 17:06:31.730: E/AndroidRuntime(2012): at dalvik.system.NativeStart.main(Native Method)
03-15 17:06:31.730: E/AndroidRuntime(2012): Caused by:
java.lang.reflect.InvocationTargetException
03-15 17:06:31.730: E/AndroidRuntime(2012): at java.lang.reflect.Method.invokeNative(Native
Method)
03-15 17:06:31.730: E/AndroidRuntime(2012): at java.lang.reflect.Method.invoke(Method.java:525)
03-15 17:06:31.730: E/AndroidRuntime(2012): at android.view.View$1.onClick(View.java:3628)
03-15 17:06:31.730: E/AndroidRuntime(2012): ... 11 more
03-15 17:06:31.730: E/AndroidRuntime(2012): Caused by: java.lang.NullPointerException
03-15 17:06:31.730: E/AndroidRuntime(2012): at
com.example.androidrest_client.MainActivity.hideKeyboard(MainActivity.java:83)
03-15 17:06:31.730: E/AndroidRuntime(2012): at
com.example.androidrest_client.MainActivity.access$0(MainActivity.java:76)
03-15 17:06:31.730: E/AndroidRuntime(2012): at
com.example.androidrest_client.MainActivity$WebServiceTask.onPreExecute(MainActivity.java:133)
03-15 17:06:31.730: E/AndroidRuntime(2012): at
android.os.AsyncTask.executeOnExecutor(AsyncTask.java:586)
03-15 17:06:31.730: E/AndroidRuntime(2012): at android.os.AsyncTask.execute(AsyncTask.java:534)
03-15 17:06:31.730: E/AndroidRuntime(2012): at
com.example.androidrest_client.MainActivity.retrieveSampleData(MainActivity.java:53)
03-15 17:06:31.730: E/AndroidRuntime(2012): ... 14 more
我使用以下布局：
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context=".Register" >
<TextView
android:id="@+id/textView1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentTop="true"
android:layout_marginTop="71dp"
android:text="@string/downloadRoutines"
android:textAppearance="?android:attr/textAppearanceLarge" />
<Button
android:id="@+id/download"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_below="@+id/textView1"
android:layout_centerHorizontal="true"
android:layout_marginTop="46dp"
android:onClick="retrieveSampleData"
android:text="@string/download"
/>
</RelativeLayout>
这是MainActivity类：
public class MainActivity extends Activity {
private static final String SERVICE_URL = "http://10.0.2.2:8085/ClinicWebApp/rest/routine
/sample";
private static final String TAG = "MainActivity";
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
public void retrieveSampleData(View vw){
Toast.makeText(MainActivity.this, "Button Clicked", Toast.LENGTH_SHORT).show();
String sampleURL = SERVICE_URL;
WebServiceTask wst = new
WebServiceTask(WebServiceTask.GET_TASK,MainActivity.this,"GETting data...");
wst.execute(new String[] { sampleURL });
}
public void handleResponse(String response) {
try {
JSONObject jso = new JSONObject(response);
for(int i=0;i<jso.length();i++){
System.out.println(jso.toString());
}
} catch (Exception e) {
Log.e(TAG, e.getLocalizedMessage(), e);
}
}
private void hideKeyboard() {
InputMethodManager inputManager = (InputMethodManager) MainActivity.this
.getSystemService(Context.INPUT_METHOD_SERVICE);
inputManager.hideSoftInputFromWindow(
MainActivity.this.getCurrentFocus()
.getWindowToken(), InputMethodManager.HIDE_NOT_ALWAYS);
}
private class WebServiceTask extends AsyncTask<String, Integer, String> {
public static final int POST_TASK = 1;
public static final int GET_TASK = 2;
private static final String TAG = "WebServiceTask";
// connection timeout, in milliseconds (waiting to connect)
private static final int CONN_TIMEOUT = 3000;
// socket timeout, in milliseconds (waiting for data)
private static final int SOCKET_TIMEOUT = 5000;
private int taskType = GET_TASK;
private Context mContext = null;
private String processMessage = "Processing...";
private ArrayList<NameValuePair> params = new ArrayList<NameValuePair>();
private ProgressDialog pDlg = null;
public WebServiceTask(int taskType, Context mContext, String processMessage) {
this.taskType = taskType;
this.mContext = mContext;
this.processMessage = processMessage;
}
public void addNameValuePair(String name, String value) {
params.add(new BasicNameValuePair(name, value));
}
private void showProgressDialog() {
pDlg = new ProgressDialog(mContext);
pDlg.setMessage(processMessage);
pDlg.setProgressDrawable(mContext.getWallpaper());
pDlg.setProgressStyle(ProgressDialog.STYLE_SPINNER);
pDlg.setCancelable(false);
pDlg.show();
}
@Override
protected void onPreExecute() {
hideKeyboard();
showProgressDialog();
}
protected String doInBackground(String... urls) {
String url = urls[0];
String result = "";
HttpResponse response = doResponse(url);
if (response == null) {
return result;
} else {
try {
result = inputStreamToString(response.getEntity().getContent());
} catch (IllegalStateException e) {
Log.e(TAG, e.getLocalizedMessage(), e);
} catch (IOException e) {
Log.e(TAG, e.getLocalizedMessage(), e);
}
}
return result;
}
@Override
protected void onPostExecute(String response) {
handleResponse(response);
pDlg.dismiss();
}
// Establish connection and socket (data retrieval) timeouts
private HttpParams getHttpParams() {
HttpParams htpp = new BasicHttpParams();
HttpConnectionParams.setConnectionTimeout(htpp, CONN_TIMEOUT);
HttpConnectionParams.setSoTimeout(htpp, SOCKET_TIMEOUT);
return htpp;
}
private HttpResponse doResponse(String url) {
// Use our connection and data timeouts as parameters for our
// DefaultHttpClient
HttpClient httpclient = new DefaultHttpClient(getHttpParams());
HttpResponse response = null;
try {
switch (taskType) {
case POST_TASK:
HttpPost httppost = new HttpPost(url);
// Add parameters
httppost.setEntity(new UrlEncodedFormEntity(params));
response = httpclient.execute(httppost);
break;
case GET_TASK:
HttpGet httpget = new HttpGet(url);
response = httpclient.execute(httpget);
break;
}
} catch (Exception e) {
Log.e(TAG, e.getLocalizedMessage(), e);
}
return response;
}
private String inputStreamToString(InputStream is) {
String line = "";
StringBuilder total = new StringBuilder();
// Wrap a BufferedReader around the InputStream
BufferedReader rd = new BufferedReader(new InputStreamReader(is));
try {
// Read response until the end
while ((line = rd.readLine()) != null) {
total.append(line);
}
} catch (IOException e) {
Log.e(TAG, e.getLocalizedMessage(), e);
}
// Return full string
return total.toString();
}
}
}
你能帮帮我吗？任何想法都会受到赞赏。