[英]Android app crashing on run: 'java.lang.String android.content.Context.getPackageName()'
我想知道是否有人可以提供幫助。 每次我運行android應用項目時，它都會崩潰。 我已經將其縮小為單個功能，但是我不知道為什么它崩潰了！
錯誤：
05-07 17:38:22.059 3952-3986/com.tfs.appname W/System: ClassLoader referenced unknown path: /data/data/com.tfs.appname/lib
05-07 17:38:22.122 3952-3952/com.tfs.appname D/AndroidRuntime: Shutting down VM
05-07 17:38:22.123 3952-3952/com.tfs.appname E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.tfs.appname, PID: 3952
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.tfs.appname/com.tfs.appname.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String android.content.Context.getPackageName()' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2416)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
at android.app.ActivityThread.handleRelaunchActivity(ActivityThread.java:4077)
at android.app.ActivityThread.-wrap15(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1350)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String android.content.Context.getPackageName()' on a null object reference
at android.content.ContextWrapper.getPackageName(ContextWrapper.java:133)
at android.app.Activity.getLocalClassName(Activity.java:5205)
at android.app.Activity.getPreferences(Activity.java:5239)
at com.tfs.appname.helpers.isLoggedIn(helpers.java:99)
at com.tfs.appname.MainActivity$override.onCreate(MainActivity.java:35)
at com.tfs.appname.MainActivity$override.access$dispatch(MainActivity.java)
at com.tfs.appname.MainActivity.onCreate(MainActivity.java:0)
at android.app.Activity.performCreate(Activity.java:6237)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1107)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2369)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
at android.app.ActivityThread.handleRelaunchActivity(ActivityThread.java:4077)
at android.app.ActivityThread.-wrap15(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1350)
at android.os.Handler.dispatchMessage(Handler.java:102)
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)
05-07 17:38:30.716 3952-3952/com.tfs.appname I/Process: Sending signal. PID: 3952 SIG: 9
MainActivity.java：
package com.tfs.appname;
import android.content.Intent;
import android.net.Uri;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import com.google.android.gms.appindexing.Action;
import com.google.android.gms.appindexing.AppIndex;
import com.google.android.gms.common.api.GoogleApiClient;
public class MainActivity extends AppCompatActivity {
/**
* ATTENTION: This was auto-generated to implement the App Indexing API.
* See https://g.co/AppIndexing/AndroidStudio for more information.
*/
private GoogleApiClient client;
Button LoginButton, RegisterButton;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
final helpers helpers = new helpers();
client = new GoogleApiClient.Builder(this).addApi(AppIndex.API).build();
Button LoginButton = (Button) findViewById(R.id.button_login);
Button RegisterButton = (Button) findViewById(R.id.button_register);
if (helpers.isLoggedIn()) {
startActivity(new Intent(MainActivity.this, Dashboard.class));
}
RegisterButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
startActivity(new Intent(MainActivity.this, Register.class));
}
});
LoginButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
startActivity(new Intent(MainActivity.this, Login.class));
}
});
}
@Override
public void onStart() {
super.onStart();
// ATTENTION: This was auto-generated to implement the App Indexing API.
// See https://g.co/AppIndexing/AndroidStudio for more information.
client.connect();
Action viewAction = Action.newAction(
Action.TYPE_VIEW, // TODO: choose an action type.
"Main Page", // TODO: Define a title for the content shown.
// TODO: If you have web page content that matches this app activity's content,
// make sure this auto-generated web page URL is correct.
// Otherwise, set the URL to null.
Uri.parse("http://host/path"),
// TODO: Make sure this auto-generated app URL is correct.
Uri.parse("android-app://com.tfs.appname/http/host/path")
);
AppIndex.AppIndexApi.start(client, viewAction);
}
@Override
public void onStop() {
super.onStop();
// ATTENTION: This was auto-generated to implement the App Indexing API.
// See https://g.co/AppIndexing/AndroidStudio for more information.
Action viewAction = Action.newAction(
Action.TYPE_VIEW, // TODO: choose an action type.
"Main Page", // TODO: Define a title for the content shown.
// TODO: If you have web page content that matches this app activity's content,
// make sure this auto-generated web page URL is correct.
// Otherwise, set the URL to null.
Uri.parse("http://host/path"),
// TODO: Make sure this auto-generated app URL is correct.
Uri.parse("android-app://com.tfs.appname/http/host/path")
);
AppIndex.AppIndexApi.end(client, viewAction);
client.disconnect();
}
}
登錄Java：
package com.tfs.appname;
import android.content.Context;
import android.content.Intent;
import android.content.SharedPreferences;
import android.net.Uri;
import android.os.Bundle;
import android.preference.PreferenceManager;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;
import com.google.android.gms.appindexing.Action;
import com.google.android.gms.appindexing.AppIndex;
import com.google.android.gms.common.api.GoogleApiClient;
import com.kosalgeek.asynctask.AsyncResponse;
import com.kosalgeek.asynctask.PostResponseAsyncTask;
import org.json.JSONException;
import org.json.JSONObject;
import java.util.HashMap;
import static android.app.PendingIntent.getActivity;
public class Login extends AppCompatActivity implements AsyncResponse {
Button LoginSubmitButton, LoginRegisterButton;
EditText LoginEmail, LoginPassword;
/**
* ATTENTION: This was auto-generated to implement the App Indexing API.
* See https://g.co/AppIndexing/AndroidStudio for more information.
*/
private GoogleApiClient client;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_login);
final helpers helpers = new helpers();
final EditText LoginEmail = (EditText) findViewById(R.id.login_email);
final EditText LoginPassword = (EditText) findViewById(R.id.login_password);
Button LoginSubmitButton = (Button) findViewById(R.id.login_submit);
Button LoginRegisterButton = (Button) findViewById(R.id.login_register_button);
LoginRegisterButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
startActivity(new Intent(Login.this, Register.class));
}
});
assert LoginSubmitButton != null;
LoginSubmitButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
final Context context = getApplicationContext();
int duration = Toast.LENGTH_SHORT;
if (helpers.isEmpty(LoginEmail)) {
CharSequence text = "Please enter your email address.";
Toast toast = Toast.makeText(context, text, duration);
toast.show();
} else {
if (helpers.isEmpty(LoginPassword)) {
CharSequence text = "Please enter your password.";
Toast toast = Toast.makeText(context, text, duration);
toast.show();
} else {
if (helpers.isValidEmail(LoginEmail))
if (helpers.isValidPassword(LoginPassword)) {
HashMap<String, String> postData = new HashMap<String, String>();
postData.put("emailaddress", LoginEmail.getText().toString());
postData.put("password", LoginPassword.getText().toString());
final PostResponseAsyncTask loginTask = new PostResponseAsyncTask(Login.this, postData, new AsyncResponse() {
@Override
public void processFinish(String s) {
JSONObject results = null;
String result_status = null;
String MID = null;
String MT = null;
try {
results = new JSONObject(s);
result_status = results.getString("STATUS");
MID = results.getString("MID");
MT = results.getString("MT");
} catch (JSONException e) {
e.printStackTrace();
}
if (result_status.equalsIgnoreCase("success")) {
SharedPreferences sharedPref = Login.this.getPreferences(Context.MODE_PRIVATE);
SharedPreferences.Editor editor = sharedPref.edit();
editor.putString("MID", MID);
editor.putString("MTOK", MT);
editor.commit();
startActivity(new Intent(Login.this, Dashboard.class));
} else {
Context context = getApplicationContext();
int duration = Toast.LENGTH_SHORT;
CharSequence text = result_status;
Toast toast = Toast.makeText(context, text, duration);
toast.show();
}
}
});
loginTask.execute("http://192.168.1.64/app/test.php");
} else {
CharSequence text = "Invalid password.";
Toast toast = Toast.makeText(context, text, duration);
toast.show();
}
else {
CharSequence text = "Invalid email address.";
Toast toast = Toast.makeText(context, text, duration);
toast.show();
}
}
}
}
});
// ATTENTION: This was auto-generated to implement the App Indexing API.
// See https://g.co/AppIndexing/AndroidStudio for more information.
client = new GoogleApiClient.Builder(this).addApi(AppIndex.API).build();
}
@Override
public void processFinish(String s) {
}
@Override
public void onStart() {
super.onStart();
// ATTENTION: This was auto-generated to implement the App Indexing API.
// See https://g.co/AppIndexing/AndroidStudio for more information.
client.connect();
Action viewAction = Action.newAction(
Action.TYPE_VIEW, // TODO: choose an action type.
"Login Page", // TODO: Define a title for the content shown.
// TODO: If you have web page content that matches this app activity's content,
// make sure this auto-generated web page URL is correct.
// Otherwise, set the URL to null.
Uri.parse("http://host/path"),
// TODO: Make sure this auto-generated app URL is correct.
Uri.parse("android-app://com.tfs.appname/http/host/path")
);
AppIndex.AppIndexApi.start(client, viewAction);
}
@Override
public void onStop() {
super.onStop();
// ATTENTION: This was auto-generated to implement the App Indexing API.
// See https://g.co/AppIndexing/AndroidStudio for more information.
Action viewAction = Action.newAction(
Action.TYPE_VIEW, // TODO: choose an action type.
"Login Page", // TODO: Define a title for the content shown.
// TODO: If you have web page content that matches this app activity's content,
// make sure this auto-generated web page URL is correct.
// Otherwise, set the URL to null.
Uri.parse("http://host/path"),
// TODO: Make sure this auto-generated app URL is correct.
Uri.parse("android-app://com.tfs.appname/http/host/path")
);
AppIndex.AppIndexApi.end(client, viewAction);
client.disconnect();
}
}
Helpers.Java：
package com.tfs.appname;
import android.content.Context;
import android.content.Intent;
import android.content.SharedPreferences;
import android.net.Uri;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.text.TextUtils;
import android.util.Patterns;
import android.widget.EditText;
import android.widget.Toast;
import com.google.android.gms.appindexing.Action;
import com.google.android.gms.appindexing.AppIndex;
import com.google.android.gms.common.api.GoogleApiClient;
import com.kosalgeek.asynctask.AsyncResponse;
import com.kosalgeek.asynctask.PostResponseAsyncTask;
import org.json.JSONException;
import org.json.JSONObject;
import java.io.BufferedInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.net.URL;
import java.net.URLConnection;
import java.util.HashMap;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
/**
* Created by Offic on 03/05/2016.
*/
public class helpers extends AppCompatActivity implements AsyncResponse {
/**
* ATTENTION: This was auto-generated to implement the App Indexing API.
* See https://g.co/AppIndexing/AndroidStudio for more information.
*/
private GoogleApiClient client;
boolean isEmpty(EditText etText) {
return etText.getText().toString().trim().length() <= 0;
}
public boolean isValidEmail(EditText email) {
if (TextUtils.isEmpty(email.getText())) {
return false;
} else {
return Patterns.EMAIL_ADDRESS.matcher(email.getText()).matches();
}
}
public boolean isValidPassword(EditText password) {
String regExpn = "^[a-z0-9_]{6,24}$";
CharSequence inputStr = password.getText();
Pattern pattern = Pattern.compile(regExpn, Pattern.CASE_INSENSITIVE);
Matcher matcher = pattern.matcher(inputStr);
if (matcher.matches()) {
return true;
} else {
return false;
}
}
private boolean verifySession(String MID, String MTOK) {
HashMap<String, String> postData = new HashMap<String, String>();
postData.put("MID", MID);
postData.put("MTOK", MTOK);
final Boolean[] Ret = {false};
final PostResponseAsyncTask loginTask = new PostResponseAsyncTask(this, postData, new AsyncResponse() {
@Override
public void processFinish(String s) {
JSONObject results = null;
String result_status = null;
try {
results = new JSONObject(s);
result_status = results.getString("STATUS");
} catch (JSONException e) {
e.printStackTrace();
}
if (result_status == "success") {
Ret[0] = true;
} else {
Ret[0] = false;
}
}
});
loginTask.execute("http://192.168.1.64/app/test.php");
return Ret[0];
}
public boolean isLoggedIn() {
SharedPreferences sharedPref = this.getPreferences(Context.MODE_PRIVATE);
String MID = sharedPref.getString("MID", null);
String MT = sharedPref.getString("MTOK", null);
if (MID == null || MT == null) {
return false;
} else {
return verifySession(MID, MT);
}
}
@Override
public void processFinish(String s) {
}
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
client = new GoogleApiClient.Builder(this).addApi(AppIndex.API).build();
}
@Override
public void onStart() {
super.onStart();
client.connect();
Action viewAction = Action.newAction(
Action.TYPE_VIEW, // TODO: choose an action type.
"helpers Page", // TODO: Define a title for the content shown.
Uri.parse("http://host/path"),
Uri.parse("android-app://com.tfs.appname/http/host/path")
);
AppIndex.AppIndexApi.start(client, viewAction);
}
@Override
public void onStop() {
super.onStop();
Action viewAction = Action.newAction(
Action.TYPE_VIEW, // TODO: choose an action type.
"helpers Page", // TODO: Define a title for the content shown.
// TODO: If you have web page content that matches this app activity's content,
// make sure this auto-generated web page URL is correct.
// Otherwise, set the URL to null.
Uri.parse("http://host/path"),
// TODO: Make sure this auto-generated app URL is correct.
Uri.parse("android-app://com.tfs.appname/http/host/path")
);
AppIndex.AppIndexApi.end(client, viewAction);
client.disconnect();
}
}
任何幫助將不勝感激！ 我對這門語言非常陌生，因此我仍在掌握所有語言的工作方式。
非常感謝
您的設計中存在一個重大缺陷。 錯誤很明顯。 在這條線
final helpers helpers = new helpers();
您正在嘗試創建一個活動的對象，這是非常非常糟糕的做法。 您不能簡單地創建此類活動的對象。 Android中的所有Activity必須經歷Activity生命周期，以便它們具有有效的上下文。 在這種情況下，有效上下文不會附加到幫助程序實例。 所以結果
SharedPreferences sharedPref = this.getPreferences(Context.MODE_PRIVATE);
導致空指針，因為“ this”為空。 （為什么？因為這是指尚未創建的上下文，因為未使用startActivity（intent）啟動該活動）
另一件事雖然不是錯誤，但您必須使用以大寫字母開頭的活動名稱。 這是遵循的約定，它將使您的代碼更具可讀性。 由於大寫和小寫名稱的奇怪使用，您的代碼非常混亂。 您使用小寫字母聲明類，而在某些情況下變量則使用大寫字母。 引起混亂。 規則是類，接口等應以大寫字母和變量（小寫）開頭。
那么在這種情況下您該怎么辦？
您永遠不會啟動Helper活動，並且我認為您無需向用戶展示它。 那就是它需要做一些工作而無需用戶交互。 您應該提供服務。 然后使用startService(intent).啟動它startService(intent). 或者您也可以將其創建為Java類，具體取決於您的用例。
編輯：順便說一句，我回答了另一個類似的問題，同樣的問題，但今天晚些時候涉及服務。
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[英]Attempt to invoke virtual method 'java.lang.String android.content.Context.getPackageName()' on a null object reference error
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[英]app crash with android.content.Context.getPackageName()' on a null object reference
android.content.Context.getPackageName() 在 null object 參考
[英]android.content.Context.getPackageName() on a null object reference
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[英]Exception when Intent Data to another Activity android.content.Context.getPackageName()
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[英]Android app returns "Error: Attempt to invoke virtual method 'java.lang.Object android.content.Context.getSystemService(java.lang.String)"
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