Question

我正在创建一个应用程序来保存名称并使用Spinner控件，但它一直给我一个Null Pointer Exception。

它说：

Attempt to invoke interface method 'android.content.SharedPreferences$Editor android.content.SharedPreferences$Editor.putInt(java.lang.String, int)' on a null object reference 
at com.example.shubham.theroster.MainActivity.onItemSelected

这是MainActivity.java

public class MainActivity extends AppCompatActivity implements AdapterView.OnItemSelectedListener {
    EditText editText;
    SharedPreferences prefs;
    SharedPreferences.Editor editor;
    CheckBox box1, box2;
    Spinner spinner;
    int spinnerData;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        prefs = getSharedPreferences("settings", MODE_PRIVATE);
        editText = (EditText) findViewById(R.id.editText);
        box1 = (CheckBox) findViewById(R.id.checkBox);
        box2 = (CheckBox) findViewById(R.id.checkBox2);
        spinner = (Spinner) findViewById(R.id.spinner);
        spinner.setOnItemSelectedListener(this);
        spinnerElement();
        loadDataPreference();
    }

    public void save(View v) {
        editor = prefs.edit();
        // 1.  Name
        editor.putString("name", editText.getText().toString());
        //2. checkbox
        if (box1.isChecked()) {
            // steady=true;
            editor.putString("status", "Not Steady");
        } else if (box2.isChecked()) {
            //notSteady=true;
            editor.putString("status", "Steady");
        }
        /*CheckBox cb = (CheckBox) findViewById(checkBox);
        boolean bCheckBox = cb.isChecked();
        editor.putInt("", bCheckBox ? 1 : 0);*/
        editor.commit();
        Toast.makeText(this, "Saved", Toast.LENGTH_SHORT).show();
    }

    public void loadDataPreference() {
        String str = prefs.getString("name", "");
        editText.setText(str);
        String status = prefs.getString("status", "");
        if (status.equals("Steady")) {
            box2.setChecked(true);
        } else {
            box1.setChecked(true);
        }
        Toast.makeText(MainActivity.this, status, Toast.LENGTH_LONG).show();
        spinner.setSelection(prefs.getInt("spinnerStatus", 0));
    }

    @Override
    public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
        editor.putInt("spinnerStatus", position);

        Toast.makeText(MainActivity.this, parent.getItemAtPosition(position).toString(), Toast.LENGTH_LONG).show();
    }

    @Override
    public void onNothingSelected(AdapterView<?> parent) {
    }

    public void spinnerElement() {
        ArrayAdapter<CharSequence> adapter = ArrayAdapter.createFromResource(this,
                R.array.color_arrays, android.R.layout.simple_spinner_item);
        adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
        spinner.setAdapter(adapter);
    }
}

Answer 1

您用于编辑数据的编辑器对象为null，只需写入

editor = prefs .edit();

下面

 prefs = getSharedPreferences("settings", MODE_PRIVATE);

在您的onCreate()方法中，所有内容都将按计划进行。您正在使用特定方法初始化编辑器，这会使您的内容变得模棱两可。

Spinner控件上共享首选项的空指针异常

1 个答案: