我想知道是否有人可以提供帮助。每次我运行我的Android应用程序项目时都会崩溃。我把它缩小到一个单一的功能，但我不知道它为什么会崩溃！
ERROR：
05-07 17:38:22.059 3952-3986/com.tfs.adihub W/System: ClassLoader referenced unknown path: /data/data/com.tfs.adihub/lib
05-07 17:38:22.122 3952-3952/com.tfs.adihub D/AndroidRuntime: Shutting down VM
05-07 17:38:22.123 3952-3952/com.tfs.adihub E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.tfs.adihub, PID: 3952
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.tfs.adihub/com.tfs.adihub.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.adihub.helpers.isLoggedIn(helpers.java:99)
at com.tfs.adihub.MainActivity$override.onCreate(MainActivity.java:35)
at com.tfs.adihub.MainActivity$override.access$dispatch(MainActivity.java)
at com.tfs.adihub.MainActivity.onCreate(MainActivity.java:0)
at android.app.Activity.performCreate(Activity.java:6237)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1107)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2369)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
at android.app.ActivityThread.handleRelaunchActivity(ActivityThread.java:4077)
at android.app.ActivityThread.-wrap15(ActivityThread.java)
at android.app.ActivityThread$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.adihub I/Process: Sending signal. PID: 3952 SIG: 9
MainActivity.java：
package com.tfs.adihub;
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.adihub/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.adihub/http/host/path")
);
AppIndex.AppIndexApi.end(client, viewAction);
client.disconnect();
}
}
Login.Java：
package com.tfs.adihub;
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.adihub/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.adihub/http/host/path")
);
AppIndex.AppIndexApi.end(client, viewAction);
client.disconnect();
}
}
Helpers.Java：
package com.tfs.adihub;
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.adihub/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.adihub/http/host/path")
);
AppIndex.AppIndexApi.end(client, viewAction);
client.disconnect();
}
}
任何帮助将不胜感激！我对这种语言非常非常新，所以我仍然要掌握这一切是如何运作的。
非常感谢
答案 0 :(得分：3)
您的设计存在重大缺陷。错误很明显。在这一行
final helpers helpers = new helpers();
您正在尝试创建活动的对象，这是一种非常糟糕的做法。你不能简单地创建这样的活动对象。 Android中的所有活动都必须通过活动生命周期，以便它们附加有效的上下文。在这种情况下，有效的上下文不会附加到帮助程序实例。因此，行
SharedPreferences sharedPref = this.getPreferences(Context.MODE_PRIVATE);
导致空指针，因为'this'为null。 （为什么？因为这是指由于未使用startActivity（intent）启动活动而尚未创建的上下文）
另一件事虽然这不是错误，但您必须使用以大写字母开头的活动名称。遵循惯例，将使您的代码更具可读性。由于大写和小写名称的奇怪使用，您的代码非常混乱。您使用小写字母声明您的类，而在某些地方，变量是大写的。这会造成混乱。规则是类，接口等应该以大写字母和变量作为小写字母开始。
所以在这种情况下你做什么？
您永远不会开始您的帮助程序活动，我认为您不需要向用户显示它。这就是它需要在没有用户交互的情况下完成一些工作。你应该把它变成一种服务。然后使用startService(intent).启动它或者您也可以将其创建为Java类，具体取决于您的用例。
编辑：顺便说一下，我回答了another类似问题，但问题相同，但今天晚些时候涉及服务。