在运行我的应用程序时，我点击注册按钮，应用程序崩溃了。请在下面找到Log-cat（如果有人能解释使用log-cat的最佳方法那么棒）我还包括了Java注册表。如果还有其他信息需要评论，我会更新此消息。
04-23 21:52:07.835: D/libEGL(28588): loaded /system/lib/egl/libEGL_mali.so
04-23 21:52:07.875: D/libEGL(28588): loaded /system/lib/egl/libGLESv1_CM_mali.so
04-23 21:52:07.885: D/libEGL(28588): loaded /system/lib/egl/libGLESv2_mali.so
04-23 21:52:07.895: E/(28588): Device driver API match
04-23 21:52:07.895: E/(28588): Device driver API version: 23
04-23 21:52:07.895: E/(28588): User space API version: 23
04-23 21:52:07.895: E/(28588): mali: REVISION=Linux-r3p2-01rel3 BUILD_DATE=Wed Oct 9 21:05:57 KST 2013
04-23 21:52:08.000: D/OpenGLRenderer(28588): Enabling debug mode 0
04-23 21:52:24.925: D/AndroidRuntime(28588): Shutting down VM
04-23 21:52:24.925: W/dalvikvm(28588): threadid=1: thread exiting with uncaught exception (group=0x41ba8700)
04-23 21:52:24.930: E/AndroidRuntime(28588): FATAL EXCEPTION: main
04-23 21:52:24.930: E/AndroidRuntime(28588): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.loggedin/com.loggedin.Register}: java.lang.NullPointerException
04-23 21:52:24.930: E/AndroidRuntime(28588): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2295)
04-23 21:52:24.930: E/AndroidRuntime(28588): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2349)
04-23 21:52:24.930: E/AndroidRuntime(28588): at android.app.ActivityThread.access$700(ActivityThread.java:159)
04-23 21:52:24.930: E/AndroidRuntime(28588): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1316)
04-23 21:52:24.930: E/AndroidRuntime(28588): at android.os.Handler.dispatchMessage(Handler.java:99)
04-23 21:52:24.930: E/AndroidRuntime(28588): at android.os.Looper.loop(Looper.java:176)
04-23 21:52:24.930: E/AndroidRuntime(28588): at android.app.ActivityThread.main(ActivityThread.java:5419)
04-23 21:52:24.930: E/AndroidRuntime(28588): at java.lang.reflect.Method.invokeNative(Native Method)
04-23 21:52:24.930: E/AndroidRuntime(28588): at java.lang.reflect.Method.invoke(Method.java:525)
04-23 21:52:24.930: E/AndroidRuntime(28588): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1046)
04-23 21:52:24.930: E/AndroidRuntime(28588): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:862)
04-23 21:52:24.930: E/AndroidRuntime(28588): at dalvik.system.NativeStart.main(Native Method)
04-23 21:52:24.930: E/AndroidRuntime(28588): Caused by: java.lang.NullPointerException
04-23 21:52:24.930: E/AndroidRuntime(28588): at com.loggedin.Register.onCreate(Register.java:83)
04-23 21:52:24.930: E/AndroidRuntime(28588): at android.app.Activity.performCreate(Activity.java:5372)
04-23 21:52:24.930: E/AndroidRuntime(28588): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1104)
04-23 21:52:24.930: E/AndroidRuntime(28588): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2257)
以下代码是注册页面
package com.loggedin;
import android.app.Activity;
import android.app.ProgressDialog;
import android.content.Context;
import android.content.Intent;
import android.net.ConnectivityManager;
import android.net.NetworkInfo;
import android.os.AsyncTask;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;
import com.loggedin.internal.DatabaseHandler;
import com.loggedin.internal.UserFunctions;
import org.json.JSONException;
import org.json.JSONObject;
import java.io.IOException;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
public class Register extends Activity {
/**
* JSON Response node names.
**/
private static String KEY_SUCCESS = "success";
private static String KEY_UID = "id";
private static String KEY_FIRSTNAME = "FirstName";
private static String KEY_LASTNAME = "LastName";
private static String KEY_USERNAME = "Username";
private static String KEY_EMAIL = "email";
private static String KEY_DOB = "DOB";
private static String KEY_CREATED_AT = "created_at";
private static String KEY_ERROR = "error";
/**
* Defining layout items.
**/
EditText inputFirstName;
EditText inputLastName;
EditText inputUsername;
EditText inputEmail;
EditText inputDOB;
EditText inputPassword;
Button btnRegister;
TextView registerErrorMsg;
/**
* Called when the activity is first created.
*/
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_register);
/**
* Defining all layout items
**/
inputFirstName = (EditText) findViewById(R.id.FirstName);
inputLastName = (EditText) findViewById(R.id.LastName);
inputUsername = (EditText) findViewById(R.id.Username);
inputEmail = (EditText) findViewById(R.id.email);
inputDOB = (EditText) findViewById(R.id.DOB);
inputPassword = (EditText) findViewById(R.id.Password);
btnRegister = (Button) findViewById(R.id.registerbtn1);
registerErrorMsg = (TextView) findViewById(R.id.register_error);
/**
* Button which Switches back to the login screen on clicked
**/
Button login = (Button) findViewById(R.id.bktologinbtn);
login.setOnClickListener(new View.OnClickListener() {
public void onClick(View view) {
Intent myIntent = new Intent(view.getContext(), Login.class);
startActivityForResult(myIntent, 0);
finish();
}
});
/**
* Register Button click event.
* A Toast is set to alert when the fields are empty.
* Another toast is set to alert Username must be 5 characters.
**/
btnRegister.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
if ( ( !inputUsername.getText().toString().equals("")) && ( !inputPassword.getText().toString().equals("")) && ( !inputFirstName.getText().toString().equals("")) && ( !inputLastName.getText().toString().equals("")) && ( !inputDOB.getText().toString().equals("")) && ( !inputEmail.getText().toString().equals("")) )
{
if ( inputUsername.getText().toString().length() > 4 ){
InternetAsync(view);
}
else
{
Toast.makeText(getApplicationContext(),
"Username should be minimum 5 characters", Toast.LENGTH_SHORT).show();
}
}
else
{
Toast.makeText(getApplicationContext(),
"One or more fields are empty", Toast.LENGTH_SHORT).show();
}
}
});
}
/**
* Async Task to check whether internet connection is working
**/
private class InternetCheck extends AsyncTask<String, Boolean, Boolean> {
private ProgressDialog nDialog;
@Override
protected void onPreExecute(){
super.onPreExecute();
nDialog = new ProgressDialog(Register.this);
nDialog.setMessage("Loading..");
nDialog.setTitle("Checking Network");
nDialog.setIndeterminate(false);
nDialog.setCancelable(true);
nDialog.show();
}
@Override
protected Boolean doInBackground(String... args){
/**
* Gets current device state and checks for working internet connection by trying Google.
**/
ConnectivityManager cm = (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);
NetworkInfo netInfo = cm.getActiveNetworkInfo();
if (netInfo != null && netInfo.isConnected()) {
try {
URL url = new URL("http://www.google.com");
HttpURLConnection urlc = (HttpURLConnection) url.openConnection();
urlc.setConnectTimeout(3000);
urlc.connect();
if (urlc.getResponseCode() == 200) {
return true;
}
} catch (MalformedURLException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
return false;
}
@Override
protected void onPostExecute(Boolean th){
if(th == true){
nDialog.dismiss();
new ProcessRegister().execute();
}
else{
nDialog.dismiss();
registerErrorMsg.setText("Error in Network Connection");
}
}
}
private class ProcessRegister extends AsyncTask <String, String, JSONObject>{
/**
* Defining Process dialog
**/
private ProgressDialog pDialog;
String email,Password,FirstName,LastName,DOB,Username;
@Override
protected void onPreExecute() {
super.onPreExecute();
inputUsername = (EditText) findViewById(R.id.Username);
inputPassword = (EditText) findViewById(R.id.Password);
FirstName = inputFirstName.getText().toString();
LastName = inputLastName.getText().toString();
email = inputEmail.getText().toString();
DOB = inputDOB.getText().toString();
Username= inputUsername.getText().toString();
Password = inputPassword.getText().toString();
pDialog = new ProgressDialog(Register.this);
pDialog.setTitle("Contacting Servers");
pDialog.setMessage("Registering ...");
pDialog.setIndeterminate(false);
pDialog.setCancelable(true);
pDialog.show();
}
@Override
protected JSONObject doInBackground(String... args) {
UserFunctions userFunction = new UserFunctions();
JSONObject json = userFunction.registerUser(FirstName, LastName, DOB, email, Username, Password);
return json;
}
@Override
protected void onPostExecute(JSONObject json) {
/**
* Checks for success message.
**/
try {
if (json.getString(KEY_SUCCESS) != null) {
registerErrorMsg.setText("");
String res = json.getString(KEY_SUCCESS);
String red = json.getString(KEY_ERROR);
if(Integer.parseInt(res) == 1){
pDialog.setTitle("Getting Data");
pDialog.setMessage("Loading Info");
registerErrorMsg.setText("Successfully Registered");
DatabaseHandler db = new DatabaseHandler(getApplicationContext());
JSONObject json_user = json.getJSONObject("user");
/**
* Removes all the previous data in the SQlite database
**/
UserFunctions logout = new UserFunctions();
logout.logoutUser(getApplicationContext());
db.addUser(json_user.getString(KEY_FIRSTNAME),json_user.getString(KEY_LASTNAME),json_user.getString(KEY_EMAIL),json_user.getString(KEY_USERNAME),json_user.getString(KEY_UID),json_user.getString(KEY_CREATED_AT));
/**
* Stores registered data in SQlite Database
* Launch Registered screen
**/
Intent registered = new Intent(getApplicationContext(),Registered.class);
/**
* Close all views before launching Registered screen
**/
registered.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
pDialog.dismiss();
startActivity(registered);
finish();
}
else if (Integer.parseInt(red) ==2){
pDialog.dismiss();
registerErrorMsg.setText("User already exists");
}
else if (Integer.parseInt(red) ==3){
pDialog.dismiss();
registerErrorMsg.setText("Invalid Email id");
}
}
else{
pDialog.dismiss();
registerErrorMsg.setText("Error occured in registration");
}
} catch (JSONException e) {
e.printStackTrace();
}
}
}
public void InternetAsync(View view){
new InternetCheck().execute();
}
}
答案 0 :(得分：3)
使用logcat时的一些建议...
E / AndroidRuntime（28588）：引起：java.lang.NullPointerException
E / AndroidRuntime（28588）：at
com.loggedin.Register.onCreate（ Register.java:83 ）
你总是可以快速进行文本搜索，检查所造成的：你可以找出你出错的地方.Logcat还会在你的案例行＃83中显示错误被抛出的位置。
我建议也要考虑如何正确使用调试器，这非常重要：
答案 1 :(得分：2)
正如Mike已经说过的，调试器可以真正帮助您找到问题。 在这种情况下，该行是：
btnRegister.setOnClickListener(new View.OnClickListener() {
问题在于你使用findViewById：
public View findViewById (int id)
Added in API level 1
Finds a view that was identified by the id attribute from the XML that was processed in onCreate(Bundle).
Returns
The view if found or null otherwise.
这意味着findViewById返回一个空指针:)所以，在XML布局中检查你的id。
答案 2 :(得分：0)
错误是显而易见的，ppl正确地说使用了调试器和logcat ..
无论如何以下是我的意见： - 1. plz交叉检查你的xml文件activity_register.xml，它有你在这里使用的id。
因为错误发生在按钮的onclick上，然后尝试捕获异常中的所有内容，使用try-catch也可以在try-catch中单击整个按钮。添加两个具有不同消息的Toast，以识别引发异常的位置。
你也可以在获取id之后简单地添加Log msg这样的Log.e（“IS_REGISTER_BUTTON_NULL”，“Value：”+ btnRegister），如果它不为null，它将写入除null之外的其他字符。同时删除onlick中的所有内容，并查看每个字符串值，如
String uName = inputUsername.getText（）。toString（）; String pWd = inputPassword.getText（）。toString（）; 。 。
Log.e（“CHECKING_IF_STRING_ARE_NULL”，uName +“”+ pWd +“”+ eMail + .....）;
THX