-1

我在我的 LogIn 类中创建了 SharedPreference 并输入了一个方法 SavedPreference()

登录.java

public void SavePreferences(String key, String value){
    SharedPreferences sharedPreferences = PreferenceManager.getDefaultSharedPreferences(getApplicationContext());
    SharedPreferences.Editor editor = sharedPreferences.edit();

    editor.putString(key, value);
    editor.commit();

}

现在在我的其他活动中，我想通过调用方法并在单击确定按钮后添加这些参数来更新它或将字符串放入其中。

菜单.java

ok.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    String oldpassword = oldpass.getText().toString();
                    String newpassword = newpass.getText().toString();
                    if (LogIn.s.toString().equals("1234")) {
                        if (oldpassword.toString().equals("1234")) {
                            logIn.SavePreferences("password",newpassword);
                            Toast.makeText(Menu.this,"New password saved!",Toast.LENGTH_SHORT).show();
                        }
                        else {
                            Toast.makeText(Menu.this,"Old Password is not correct",Toast.LENGTH_SHORT).show();
                        }
                    }
                    else {
                        if (oldpassword.equals(LogIn.realpass)){
                            logIn.SavePreferences("password",newpassword);
                            Toast.makeText(Menu.this,"New password saved!",Toast.LENGTH_SHORT).show();
                        }
                        else{
                            Toast.makeText(Menu.this,"Old Password is not correct",Toast.LENGTH_SHORT).show();
                        }
                    }

                }
            });

但是点击确定后，我的应用程序崩溃了，LogCat 显示了这个

02-06 13:21:55.834 6327-6327/com.secsys.gagacamaso.gagacamaso E/AndroidRuntime: FATAL EXCEPTION: main
                                                                            Process: com.secsys.gagacamaso.gagacamaso, PID: 6327
                                                                            java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.Context android.content.Context.getApplicationContext()' on a null object reference
                                                                                at android.content.ContextWrapper.getApplicationContext(ContextWrapper.java:107)
                                                                                at com.secsys.gagacamaso.gagacamaso.LogIn.SavePreferences(LogIn.java:191)
                                                                                at com.secsys.gagacamaso.gagacamaso.Menu$3$1.onClick(Menu.java:133)
                                                                                at android.view.View.performClick(View.java:5198)
                                                                                at android.view.View$PerformClick.run(View.java:21147)
                                                                                at android.os.Handler.handleCallback(Handler.java:739)
                                                                                at android.os.Handler.dispatchMessage(Handler.java:95)
                                                                                at android.os.Looper.loop(Looper.java:148)
                                                                                at android.app.ActivityThread.main(ActivityThread.java:5417)
                                                                                at java.lang.reflect.Method.invoke(Native Method)
                                                                                at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
                                                                                at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)

LogIn.java:191 是这个SharedPreferences sharedPreferences = PreferenceManager.getDefaultSharedPreferences(getApplicationContext());

和 Menu.java:133 是这个logIn.SavePreferences("password",newpassword);

4

3 回答 3

3

最好在SavePreferencescontext中传递argument 

public void SavePreferences(String key, String value,Conext mContext){

 SharedPreferences sharedPreferences = PreferenceManager.getDefaultSharedPreferences(mContext);
 .....
}
于 2016-02-06T13:31:50.800 回答
0

我建议您SavePreferences(String key, String value)在 Application 类中编写函数而不是任何活动，因为它可以在多个活动中使用，然后您可以轻松地使用应用程序实例调用该函数

public class MyApplication extends Application
{
    //your app constructors and other related code
    ....
    ....

    public void SavePreferences(String key, String value){
        SharedPreferences sharedPreferences = PreferenceManager.getDefaultSharedPreferences(getApplicationContext());
        SharedPreferences.Editor editor = sharedPreferences.edit();

        editor.putString(key, value);
        editor.commit();

    }
    ....
    ....
}

public class MyActivity extends Activity{

    //your Activity code
    ....
    ....

    private void MyFunction(){
        //assuming you have a static getter for the application object
        MyApplication.getApplication().SavePreferences("password",password);

    }

}
于 2016-02-06T13:45:03.100 回答
0

制作该方法static，因为这样您就可以从activity应用程序内的任何其他地方更新它。

于 2016-02-06T13:32:30.183 回答