我是新手安卓开发者,也许这是一个愚蠢的问题,但请帮助我。在尝试保存int值时,我遇到了以下错误。
Caused by: java.lang.NullPointerException: 尝试在空对象引用上调用虚拟方法'android.content.SharedPreferences android.content.Context.getSharedPreferences(java.lang.String,int)'
这是我的代码:
SharedPreferences prefs = this.getSharedPreferences("com.example.app", Context.MODE_PRIVATE);
String value = "com.example.app.value";
int i = prefs.getInt(value, 0);
并写入
prefs.edit().putInt(number, i).apply();
我只想设置SharedPreferences,并在Activity中读取它并将其写入。我该如何解决?
编辑
public class MainActivity extends Activity {
SharedPreferences sharedpreferences;
public static final String MyPREFERENCES = "myprefs";
public static final String value = "key";
int i = sharedpreferences.getInt(value, 0);
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
sharedpreferences = getSharedPreferences(MyPREFERENCES, Context.MODE_PRIVATE);
}
public void sendMessage(View view) {
i += 1;
SharedPreferences.Editor editor = sharedpreferences.edit();
editor.putInt(value, i);
editor.apply();
}
我成功地用另一种方式保存了偏好设置,但我无法在MainActivity扩展的Activity类中读取它。
日志:
Caused by: java.lang.NullPointerException: 尝试在空对象引用上调用接口方法'int android.content.SharedPreferences.getInt(java.lang.String, int)'
SharedPreferences prefs = yourActivity.this.getSharedPreferences("com.example.app", Context.MODE_PRIVATE);
- M D