Java 创建新SharedReferences文件时出现NullPointerException

除非我错了，否则调用GetSharedReferences（“someName”，0）应该只是创建一个新文件，如果手机内存中不存在文件，对吗

不幸的是，这只是给了我一个NPE。代码和LogCat如下所示

新城级别：

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 ....
}

日志：

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)

---

编辑：好的，现在我知道问题是：在创建城市之前，您正在访问城市。因此，请参见下面的代码

@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) {
            // Here, you should run this method first
            sendCityData(cityName.getText().toString());
            gen = new Generator(getBaseContext());
            errors.clear();
            gen.createCity();
        } else {
            StringBuilder builder = new StringBuilder();
            for(String value : errors) {
                builder.append(value);
            }           
            errorList.setText(builder.toString());
            errors.clear();
        }
    }

@覆盖
公共void onClick（视图）{
布尔值canGenerate=true；
ArrayList errors=新建ArrayList（）；
开关（view.getId（））{
案例R.id.bNewNext：
如果（cityName.getText（）.toString（）.matches（“”）匹配{
错误。添加（“！结算必须有名称。\n”）；
canGenerate=false；
}
if（specific.isChecked（）&&customPop.getText（）.toString（）.matches（“”）{
错误。添加（“！输入人口数字。\n”）；
canGenerate=false；
}           
打破
}
if（canGenerate）{
//在这里，您应该首先运行这个方法
sendCityData（cityName.getText（）.toString（））；
gen=新生成器（getBaseContext（））；
错误。清除（）；
createCity将军（）；
}否则{
StringBuilder=新的StringBuilder（）；
for（字符串值：错误）{
附加（值）；
}           
errorList.setText（builder.toString（））；
错误。清除（）；
}
}

我猜在第17行，city为null，因为NewCity.city为null。我已经确定它有一个值，所以它不是null。为了确保，我将其更改为静态字符串，它给了我完全相同的错误。我仍然不确定，但是创建一个新的构造函数，它也显式地接受

City

，并从中访问名称如何？试试这个：edit.putString（“name”，“test”）.apply（）；如果你犯了同样的错误，你就知道问题不在城市。我已经做到了，现在也行了。所以问题在于我的City类没有实例化它的name变量。我不知道为什么，因为类的构造函数需要给name变量一个字符串。City类只能在onCreate方法中初始化吗？我这样做是因为在我的代码中，我在sendCityData方法（onClick中调用的方法）中初始化它，因为我从EditText中提取用户的输入，并将其作为城市名称发送给类。

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 ....
}

@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) {
            // Here, you should run this method first
            sendCityData(cityName.getText().toString());
            gen = new Generator(getBaseContext());
            errors.clear();
            gen.createCity();
        } else {
            StringBuilder builder = new StringBuilder();
            for(String value : errors) {
                builder.append(value);
            }           
            errorList.setText(builder.toString());
            errors.clear();
        }
    }