Question

所以我试图在一个no activity类中使用我的共享prefference但是我一直在我的

上获得空指针

private SharedPreferences setingPreferences = context.getSharedPreferences（“Settings”，Activity.MODE_PRIVATE）;

我该如何解决这个问题？

 public class ConnectionClass
{
    Context context;
    private SharedPreferences setingPreferences = context.getSharedPreferences("Settings", Activity.MODE_PRIVATE);
    String ip;
    String classs = "net.sourceforge.jtds.jdbc.Driver";
    String db = "ISTABLocalDB";
    String un = "istab_wpf";
    String password = "istab_!234";
    @SuppressLint("NewApi")
    public Connection CONN() {
        ip = setingPreferences.getString("server", "");
        StrictMode.ThreadPolicy policy = new StrictMode.ThreadPolicy.Builder()
                .permitAll().build();
        StrictMode.setThreadPolicy(policy);
        Connection conn = null;
        String ConnURL = null;
        try {
            Class.forName(classs);
            ConnURL = "jdbc:jtds:sqlserver://" + ip + ";"
                    + "databaseName=" + db + ";user=" + un + ";password="
                    + password + ";";
            conn = DriverManager.getConnection(ConnURL);
        } catch (SQLException se) {
            Log.e("ERRO", se.getMessage());
        } catch (ClassNotFoundException e) {
            Log.e("ERRO", e.getMessage());
        } catch (Exception e) {
            Log.e("ERRO", e.getMessage());
        }
        return conn;

Answer 1

在初始化之前使用上下文。在您的类构造函数中，将context作为参数，然后初始化您的首选项Object。

Answer 2

您需要初始化您的上下文变量。一种方法是通过在ConnectionClass中定义构造函数将上下文变量从活动类传递给此非活动类

public ConnectionClass (Context context)  
{
   this.context = context;

}

无论您要在何处实例化此类，都要通过从调用类传递上下文来实例化它。

例如，如果要从活动类中实例化，则可以通过

执行此操作

ConnectionClass conn = new ConnectionClass(MyActivity.this.getApplicationContext());

Answer 3

您必须初始化上下文。

在构造函数中获取上下文：

Context context;
private SharedPreferences setingPreferences;

public ConnectionClass(Context context){
    this.context = context;
}

public Connection CONN() {
    setingPreferences = context.getSharedPreferences("Settings", Activity.MODE_PRIVATE);
    ip = setingPreferences.getString("server", "");

    ...

或者您可以直接在您调用的方法上获取上下文：

private SharedPreferences setingPreferences;

public Connection CONN(Context context) {
    setingPreferences = context.getSharedPreferences("Settings", Activity.MODE_PRIVATE);
    ip = setingPreferences.getString("server", "");

    ...

在无活动类

3 个答案: