除非我错了，否则调用 getSharedPreferences("someName", 0) 应该只是在手机内存中不存在一个新文件时创建一个新文件，对吧？
对我来说不幸的是，这只是给了我一个 NPE。代码和 LogCat 如下。
新城类：
public class NewCity extends Activity implements OnClickListener, OnCheckedChangeListener {
public static City city;
private Generator gen;
RadioGroup popGroup;
RadioButton random, specific;
Spinner cityType, supplies;
EditText cityName, customPop;
CheckBox fishing, mining, forestry;
Button next;
TextView errorList;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.newcity);
initializeRefs();
}
private void initializeRefs() {
popGroup = (RadioGroup) findViewById(R.id.popGroup);
random = (RadioButton) findViewById(R.id.radioRandomCity);
specific = (RadioButton) findViewById(R.id.radioSpecificCity);
cityType = (Spinner) findViewById(R.id.spinCityType);
supplies = (Spinner) findViewById(R.id.spinSupplies);
cityName = (EditText) findViewById(R.id.textCityName);
customPop = (EditText) findViewById(R.id.textCustomPop);
fishing = (CheckBox) findViewById(R.id.checkFishing);
mining = (CheckBox) findViewById(R.id.checkMining);
forestry = (CheckBox) findViewById(R.id.checkForestry);
next = (Button) findViewById(R.id.bNewNext);
errorList = (TextView) findViewById(R.id.errorList);
popGroup.setOnCheckedChangeListener(this);
next.setOnClickListener(this);
customPop.setEnabled(false);
}
@Override
public void onClick(View view) {
boolean canGenerate = true;
ArrayList<String> errors = new ArrayList<String>();
switch(view.getId()) {
case R.id.bNewNext:
if(cityName.getText().toString().matches("")) {
errors.add("! Settlement must have a name.\n");
canGenerate = false;
}
if(specific.isChecked() && customPop.getText().toString().matches("")) {
errors.add("! Enter a population figure.\n");
canGenerate = false;
}
break;
}
if(canGenerate) {
gen = new Generator(getBaseContext());
errors.clear();
sendCityData(cityName.getText().toString());
gen.createCity();
} else {
StringBuilder builder = new StringBuilder();
for(String value : errors) {
builder.append(value);
}
errorList.setText(builder.toString());
errors.clear();
}
}
.... Unrelated code ....
}
生成器类：
public class Generator {
private Context context;
private City city;
private SharedPreferences storage;
public Generator(Context context) {
this.context = context;
city = NewCity.city;
storage = context.getSharedPreferences(city.getName(), Context.MODE_PRIVATE);
}
public float random(float low, float high) {
Random random = new Random();
return ((low + (high - low)) * random.nextFloat());
}
public void createCity() {
Editor edit = storage.edit();
edit.putString("NAME", city.getName()).apply();
}
}
日志猫：
10-08 20:22:28.598: E/AndroidRuntime(21336): FATAL EXCEPTION: main
10-08 20:22:28.598: E/AndroidRuntime(21336): java.lang.NullPointerException
10-08 20:22:28.598: E/AndroidRuntime(21336): at com.flawedspirit.android.citygen.Generator.<init>(Generator.java:17)
10-08 20:22:28.598: E/AndroidRuntime(21336): at com.flawedspirit.android.citygen.NewCity.onClick(NewCity.java:77)
10-08 20:22:28.598: E/AndroidRuntime(21336): at android.view.View.performClick(View.java:4203)
10-08 20:22:28.598: E/AndroidRuntime(21336): at android.view.View$PerformClick.run(View.java:17189)
10-08 20:22:28.598: E/AndroidRuntime(21336): at android.os.Handler.handleCallback(Handler.java:615)
10-08 20:22:28.598: E/AndroidRuntime(21336): at android.os.Handler.dispatchMessage(Handler.java:92)
10-08 20:22:28.598: E/AndroidRuntime(21336): at android.os.Looper.loop(Looper.java:137)
10-08 20:22:28.598: E/AndroidRuntime(21336): at android.app.ActivityThread.main(ActivityThread.java:4961)
10-08 20:22:28.598: E/AndroidRuntime(21336): at java.lang.reflect.Method.invokeNative(Native Method)
10-08 20:22:28.598: E/AndroidRuntime(21336): at java.lang.reflect.Method.invoke(Method.java:511)
10-08 20:22:28.598: E/AndroidRuntime(21336): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1004)
10-08 20:22:28.598: E/AndroidRuntime(21336): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:771)
10-08 20:22:28.598: E/AndroidRuntime(21336): at dalvik.system.NativeStart.main(Native Method)
违规语句位于 Generate 类的第 17 行。我不明白为什么它不起作用。它被传递了一个上下文和一个字符串（“city.getName（）”），它在传递它之前被初始化，所以我知道那不是空的。Generator 类的构造函数是不是放错地方了？我知道它必须在活动的 super.onCreate() 语句之后。
编辑：我的城市类的构造函数；这样做真的有效吗？
public class City {
private static final int PEOPLE_PER_SQACRE = 61;
private static final int PEOPLE_PER_SQMILE = 38850;
private String name;
private String type;
private int population;
private float sizeMi;
private float sizeAc;
private int gpLimit;
private long wealth;
private float lowPop;
private float highPop;
private boolean fishing;
private boolean mining;
private boolean forestry;
public City(String name) {
this.name = name;
}
.... Unrelated code ....
}