java.lang.NullPointerException-Android中的错误 [英] java.lang.NullPointerException- error in Android
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问题描述
我正在使用我的android应用程序的电话号码和密码创建一个简单的登录活动.我想将用户输入的电话号码传递给我的欢迎屏幕，但是问题是，当用户第一次没有注销，然后在运行应用程序后注销时，出现了以上错误.请帮助我解决此错误.
I'm creating a simple login activity using phone number and password for my android application. I want to pass the user entered a phone number to my welcome screen, but the problem is I'm getting the above error when the user didn't log out the first time and then after running the application. Please help me to solve this error.
这是我的LoginActivity.java文件，
this is my LoginActivity.java file,
public class LoginActivity extends Activity {
Button btnLogin;
Button btnLinkToRegister;
EditText inputphone_number;
EditText inputPassword;
TextView loginErrorMsg;
// JSON Response node names
private static String KEY_SUCCESS = "success";
private static String KEY_ERROR = "error";
private static String KEY_ERROR_MSG = "error_msg";
private static String KEY_UID = "uid";
private static String KEY_NAME = "name";
private static String KEY_PHONE_NUMBER = "phone_number";
private static String KEY_CREATED_AT = "created_at";
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.login);
// Importing all assets like buttons, text fields
inputphone_number = (EditText) findViewById(R.id.loginEmail);
inputPassword = (EditText) findViewById(R.id.loginPassword);
btnLogin = (Button) findViewById(R.id.btnLogin);
btnLinkToRegister = (Button) findViewById(R.id.btnLinkToRegisterScreen);
loginErrorMsg = (TextView) findViewById(R.id.login_error);
// Login button Click Event
btnLogin.setOnClickListener(new View.OnClickListener() {
public void onClick(View view) {
String phone_number = inputphone_number.getText().toString();
String password = inputPassword.getText().toString();
UserFunctions userFunction = new UserFunctions();
Log.d("Button", "Login");
JSONObject json = userFunction.loginUser(phone_number, password);
// check for login response
try {
if (json.getString(KEY_SUCCESS) != null) {
loginErrorMsg.setText("");
String res = json.getString(KEY_SUCCESS);
if(Integer.parseInt(res) == 1){
// user successfully logged in
// Store user details in SQLite Database
DatabaseHandler db = new DatabaseHandler(getApplicationContext());
JSONObject json_user = json.getJSONObject("user");
// Clear all previous data in database
userFunction.logoutUser(getApplicationContext());
db.addUser(json_user.getString(KEY_NAME), json_user.getString(KEY_PHONE_NUMBER), json.getString(KEY_UID), json_user.getString(KEY_CREATED_AT));
// Launch Dashboard Screen
Intent dashboard = new Intent(getApplicationContext(), MainActivity.class);
// this is how i sent phone number to next activity
dashboard.putExtra("phone_number", phone_number);
// Close all views before launching Dashboard
dashboard.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
startActivity(dashboard);
// Close Login Screen
finish();
}else{
// Error in login
loginErrorMsg.setText("Incorrect username/password");
}
}
} catch (JSONException e) {
e.printStackTrace();
}
}
});
// Link to Register Screen
btnLinkToRegister.setOnClickListener(new View.OnClickListener() {
public void onClick(View view) {
Intent i = new Intent(getApplicationContext(),
RegisterActivity.class);
startActivity(i);
finish();
}
});
}
}
这是MainActivity.java文件，
this is MainActivity.java file,
public class MainActivity extends Activity {
UserFunctions userFunctions;
Button btnLogout;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
/**
* Dashboard Screen for the application
* */
// Check login status in database
userFunctions = new UserFunctions();
if(userFunctions.isUserLoggedIn(getApplicationContext())){
setContentView(R.layout.dashboard);
TextView phone_number = (TextView) findViewById(R.id.userNameView);
Intent i = getIntent();
String phoneNumber = i.getExtras().getString("phone_number");
phone_number.setText(phoneNumber);
btnLogout = (Button) findViewById(R.id.btnLogout);
btnLogout.setOnClickListener(new View.OnClickListener() {
public void onClick(View arg0) {
// TODO Auto-generated method stub
userFunctions.logoutUser(getApplicationContext());
Intent login = new Intent(getApplicationContext(), LoginActivity.class);
login.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
startActivity(login);
// Closing dashboard screen
finish();
}
});
}else{
// user is not logged in show login screen
Intent login = new Intent(getApplicationContext(), LoginActivity.class);
login.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
startActivity(login);
// Closing dashboard screen
finish();
}
// setContentView(R.layout.main);
// MainDBAdapter mainDBAdapter = new MainDBAdapter(this);
DatabaseHandler mainDBHandler = new DatabaseHandler(this);
}
public void onClickedJobs(View view){
Intent intent = new Intent(this,TourNumberList.class);
startActivity(intent);
}
}
UserFunctions.java文件，
UserFunctions.java file,
public class UserFunctions {
private JSONParser jsonParser;
private static String loginURL = "http://10.0.2.2/android_login_api/";
private static String registerURL = "http://10.0.2.2/android_login_api/";
private static String login_tag = "login";
private static String register_tag = "register";
// constructor
public UserFunctions(){
jsonParser = new JSONParser();
}
/**
* function make Login Request
* @param phone_number
* @param password
* */
public JSONObject loginUser(String phone_number, String password){
// Building Parameters
List<NameValuePair> params = new ArrayList<NameValuePair>();
params.add(new BasicNameValuePair("tag", login_tag));
params.add(new BasicNameValuePair("phone_number", phone_number));
params.add(new BasicNameValuePair("password", password));
JSONObject json = jsonParser.getJSONFromUrl(loginURL, params);
// return json
// Log.e("JSON", json.toString());
return json;
}
/**
* function make Login Request
* @param name
* @param phone_number
* @param password
* */
public JSONObject registerUser(String name, String phone_number, String password){
// Building Parameters
List<NameValuePair> params = new ArrayList<NameValuePair>();
params.add(new BasicNameValuePair("tag", register_tag));
params.add(new BasicNameValuePair("name", name));
params.add(new BasicNameValuePair("phone_number", phone_number));
params.add(new BasicNameValuePair("password", password));
// getting JSON Object
JSONObject json = jsonParser.getJSONFromUrl(registerURL, params);
// return json
return json;
}
/**
* Function get Login status
* */
public boolean isUserLoggedIn(Context context){
DatabaseHandler db = new DatabaseHandler(context);
int count = db.getRowCount();
if(count > 0){
// user logged in
return true;
}
return false;
}
/**
* Function to logout user
* Reset Database
* */
public boolean logoutUser(Context context){
DatabaseHandler db = new DatabaseHandler(context);
db.resetTables();
return true;
}
}
这是LogCat错误，
This is LogCat error,
04-08 10:27:56.763: E/AndroidRuntime(342): FATAL EXCEPTION: main
04-08 10:27:56.763: E/AndroidRuntime(342): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.tourinfo/com.example.tourinfo.MainActivity}: java.lang.NullPointerException
04-08 10:27:56.763: E/AndroidRuntime(342): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1647)
04-08 10:27:56.763: E/AndroidRuntime(342): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1663)
04-08 10:27:56.763: E/AndroidRuntime(342): at android.app.ActivityThread.access$1500(ActivityThread.java:117)
04-08 10:27:56.763: E/AndroidRuntime(342): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:931)
04-08 10:27:56.763: E/AndroidRuntime(342): at android.os.Handler.dispatchMessage(Handler.java:99)
04-08 10:27:56.763: E/AndroidRuntime(342): at android.os.Looper.loop(Looper.java:123)
04-08 10:27:56.763: E/AndroidRuntime(342): at android.app.ActivityThread.main(ActivityThread.java:3683)
04-08 10:27:56.763: E/AndroidRuntime(342): at java.lang.reflect.Method.invokeNative(Native Method)
04-08 10:27:56.763: E/AndroidRuntime(342): at java.lang.reflect.Method.invoke(Method.java:507)
04-08 10:27:56.763: E/AndroidRuntime(342): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
04-08 10:27:56.763: E/AndroidRuntime(342): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
04-08 10:27:56.763: E/AndroidRuntime(342): at dalvik.system.NativeStart.main(Native Method)
04-08 10:27:56.763: E/AndroidRuntime(342): Caused by: java.lang.NullPointerException
04-08 10:27:56.763: E/AndroidRuntime(342): at com.example.tourinfo.MainActivity.onCreate(MainActivity.java:37)
04-08 10:27:56.763: E/AndroidRuntime(342): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
04-08 10:27:56.763: E/AndroidRuntime(342): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1611)
04-08 10:27:56.763: E/AndroidRuntime(342): ... 11 more
推荐答案
第37行替换
i.getExtras().getString("phone_number");
使用
i.getStringExtra("phone_number");
使用sharedpreferrence:- 保存
use sharedpreferrence :- For saving
SharedPreferences sharedPref = context.getSharedPreferences("text1",
Context.MODE_PRIVATE);
Editor editor = sharedPref.edit();
if (phone!= null) {
editor.putString("phone", phone);
}
editor.commit();
用于取回:-
SharedPreferences sharedPref = context.getSharedPreferences("text1",
Context.MODE_PRIVATE);
phone= sharedPref.getString("phone", null);
这篇关于java.lang.NullPointerException-Android中的错误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！
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