当我在我的应用程序（Template1Activity）中打开此活动时，应用程序崩溃并显示以下消息：
引起：java.lang.NullPointerException：尝试在空对象引用上调用虚方法'android.content.SharedPreferences android.content.Context.getSharedPreferences（java.lang.String，int）'
Template1Activity的代码是：
package com.idleappsinc.smartmirror;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.TextView;
/**
* Created by Luke on 04/02/2018.
*/
public class Template1Activity extends AppCompatActivity {
Preferences sharedPreferences;
TimeModule timeModule = new TimeModule();
TextView timeDisplayTextView;
TextView timeLocationTextView;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_template_1);
sharedPreferences = new Preferences(this);
timeDisplayTextView = findViewById(R.id.time_display_text_view);
timeLocationTextView = findViewById(R.id.time_location_text_view);
timeModule.startTimer(timeDisplayTextView);
timeLocationTextView.setText(timeModule.getCurrentLocation());
View decorView = getWindow().getDecorView();
int uiOptions = View.SYSTEM_UI_FLAG_HIDE_NAVIGATION | View.SYSTEM_UI_FLAG_FULLSCREEN;
decorView.setSystemUiVisibility(uiOptions);
}
}
TimeModule的代码是：
package com.idleappsinc.smartmirror;
import android.app.Activity;
import android.content.Context;
import android.location.Address;
import android.location.Geocoder;
import android.location.Location;
import android.location.LocationManager;
import android.os.Handler;
import android.widget.TextView;
import java.io.IOException;
import java.util.Calendar;
import java.util.List;
import java.util.Locale;
/**
* Created by Luke on 05/02/2018.
*/
public class TimeModule extends Activity {
Preferences sharedPreferences = new Preferences(this);
List<Address> addressList;
@SuppressWarnings({"MissingPermission"})
public String getCurrentLocation() {
String currentLocation = "";
Geocoder geocoder = new Geocoder(this, Locale.getDefault());
try {
LocationManager lm = (LocationManager) getSystemService(Context.LOCATION_SERVICE);
Location location = lm.getLastKnownLocation(LocationManager.GPS_PROVIDER);
addressList = geocoder.getFromLocation(location.getLatitude(), location.getLongitude(), 1);
String area = addressList.get(0).getLocality();
String country = addressList.get(0).getCountryCode();
currentLocation = area + ", " + country;
} catch (IOException e) {
e.printStackTrace();
}
return currentLocation;
}
public void startTimer(final TextView timeDisplayTextView) {
final Handler handler = new Handler();
Runnable runnable = new Runnable() {
@Override
public void run() {
try {
if (sharedPreferences.getBooleanValue(getResources().getString(R.string.preference_time_clock_hours))) {
// User wants 24 hour format
if (sharedPreferences.getBooleanValue(getResources().getString(R.string.preference_time_segment_seconds))) {
// User wants to see seconds
int secondsLength = String.valueOf(Calendar.getInstance().get(Calendar.SECOND)).length();
int minutesLength = String.valueOf(Calendar.getInstance().get(Calendar.MINUTE)).length();
if (secondsLength == 1) {
if (minutesLength == 1) {
// Seconds = 0-9
// Minutes = 0-9
timeDisplayTextView.setText(Calendar.getInstance().get(Calendar.HOUR_OF_DAY) + ":0" + Calendar.getInstance().get(Calendar.MINUTE) + ":0" + Calendar.getInstance().get(Calendar.SECOND));
} else {
// Seconds = 0-9
timeDisplayTextView.setText(Calendar.getInstance().get(Calendar.HOUR_OF_DAY) + ":" + Calendar.getInstance().get(Calendar.MINUTE) + ":0" + Calendar.getInstance().get(Calendar.SECOND));
}
} else {
if (minutesLength == 1) {
// Minutes = 0-9
timeDisplayTextView.setText(Calendar.getInstance().get(Calendar.HOUR_OF_DAY) + ":0" + Calendar.getInstance().get(Calendar.MINUTE) + ":" + Calendar.getInstance().get(Calendar.SECOND));
} else {
// Seconds = 0-9
timeDisplayTextView.setText(Calendar.getInstance().get(Calendar.HOUR_OF_DAY) + ":" + Calendar.getInstance().get(Calendar.MINUTE) + ":" + Calendar.getInstance().get(Calendar.SECOND));
}
timeDisplayTextView.setText(Calendar.getInstance().get(Calendar.HOUR_OF_DAY) + ":" + Calendar.getInstance().get(Calendar.MINUTE) + ":" + Calendar.getInstance().get(Calendar.SECOND));
}
} else {
timeDisplayTextView.setText(Calendar.getInstance().get(Calendar.HOUR_OF_DAY) + ":" + Calendar.getInstance().get(Calendar.MINUTE));
}
} else {
// The user wants the 12 hours format
if (sharedPreferences.getBooleanValue(getResources().getString(R.string.preference_time_segment_seconds))) {
int secondsLength = String.valueOf(Calendar.getInstance().get(Calendar.SECOND)).length();
int minutesLength = String.valueOf(Calendar.getInstance().get(Calendar.MINUTE)).length();
if (secondsLength == 1) {
Calendar cal = Calendar.getInstance();
if (cal.get(Calendar.AM_PM) == Calendar.PM) {
if (minutesLength == 1) {
// Seconds = 0-9
// Minutes = 0-9
// PM
timeDisplayTextView.setText(Calendar.getInstance().get(Calendar.HOUR) + ":0" + Calendar.getInstance().get(Calendar.MINUTE) + ":0" + Calendar.getInstance().get(Calendar.SECOND) + "pm");
} else {
// Seconds = 0-9
// PM
timeDisplayTextView.setText(Calendar.getInstance().get(Calendar.HOUR) + ":" + Calendar.getInstance().get(Calendar.MINUTE) + ":0" + Calendar.getInstance().get(Calendar.SECOND) + "pm");
}
} else {
if (minutesLength == 1) {
// Seconds = 0-9
// Minutes = 0-9
// AM
timeDisplayTextView.setText(Calendar.getInstance().get(Calendar.HOUR) + ":0" + Calendar.getInstance().get(Calendar.MINUTE) + ":0" + Calendar.getInstance().get(Calendar.SECOND) + "am");
} else {
// Seconds = 0-9
// Minutes = 0-9
// AM
timeDisplayTextView.setText(Calendar.getInstance().get(Calendar.HOUR) + ":" + Calendar.getInstance().get(Calendar.MINUTE) + ":0" + Calendar.getInstance().get(Calendar.SECOND) + "am");
}
}
} else {
Calendar cal = Calendar.getInstance();
if (cal.get(Calendar.AM_PM) == Calendar.PM) {
if (minutesLength == 1) {
// Minutes = 0-9
// PM
timeDisplayTextView.setText(Calendar.getInstance().get(Calendar.HOUR) + ":0" + Calendar.getInstance().get(Calendar.MINUTE) + ":" + Calendar.getInstance().get(Calendar.SECOND) + "pm");
} else {
// PM
timeDisplayTextView.setText(Calendar.getInstance().get(Calendar.HOUR) + ":" + Calendar.getInstance().get(Calendar.MINUTE) + ":" + Calendar.getInstance().get(Calendar.SECOND) + "pm");
}
} else {
if (minutesLength == 1) {
// Minutes = 0-9
// AM
timeDisplayTextView.setText(Calendar.getInstance().get(Calendar.HOUR) + ":0" + Calendar.getInstance().get(Calendar.MINUTE) + ":" + Calendar.getInstance().get(Calendar.SECOND) + "am");
} else {
// AM
timeDisplayTextView.setText(Calendar.getInstance().get(Calendar.HOUR) + ":" + Calendar.getInstance().get(Calendar.MINUTE) + ":" + Calendar.getInstance().get(Calendar.SECOND) + "am");
}
}
}
} else {
Calendar cal = Calendar.getInstance();
if (cal.get(Calendar.AM_PM) == Calendar.PM) {
timeDisplayTextView.setText(Calendar.getInstance().get(Calendar.HOUR) + ":" + Calendar.getInstance().get(Calendar.MINUTE) + "pm");
} else {
timeDisplayTextView.setText(Calendar.getInstance().get(Calendar.HOUR) + ":" + Calendar.getInstance().get(Calendar.MINUTE) + "am");
}
}
}
} catch (Exception e) {
// TODO: handle exception
} finally {
//also call the same runnable to call it at regular interval
if (sharedPreferences.getBooleanValue(getResources().getString(R.string.preference_time_segment_seconds))) {
handler.postDelayed(this, 1000);
} else {
handler.postDelayed(this, (60 - Calendar.getInstance().get(Calendar.SECOND)) * 1000);
}
}
}
};
handler.postDelayed(runnable, (1 - Calendar.getInstance().get(Calendar.MILLISECOND)) * 1000);
}
}
错误发生在TimeModule类的以下行：Preferences sharedPreferences = new Preferences(this);
我认为这与标准Java类在调用onCreate()方法之前没有上下文这一事实有关，但我对下一步的内容毫无头绪。我尝试过一些东西，但没有运气。
Java类TimeModule只是一个Java类，而不是链接到布局的类。它扩展的erason Activity是我可以访问某些方法，例如getResources()
答案 0 :(得分：1)
由于您是在TimeModule中自己创建Template1Activity对象的。使用构造函数将Template1Activity的上下文传递给它。然后，您可以初始化构造函数中的sharedPreference。
TimeModule(Context context){
sharedPreferences = new Preferences(this);
}
答案 1 :(得分：0)
Using getResources() in non-activity class 您可以使用答案中提供的想法而不是继承活动。 通过上下文可能会导致内存泄漏并不是一个好主意。