Question

我的Android应用程序有一个登录屏幕，用户登录到他的仪表板。但我不希望用户每次关闭应用程序并启动它时都会登录（除非他们从仪表板注销）。所以，我创建了一个类来检查用户是否登录

CheckLoggedIn.java

public class CheckLoggedIn extends Activity {

    private boolean isLoggedIn = false;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        // TODO Auto-generated method stub
        super.onCreate(savedInstanceState);

        if(!isLoggedIn){
            Intent intent = new Intent(this, MainActivity.class);
            startActivity(intent);
        }else{
            Intent intent = new Intent(this, AgentHome.class);
            startActivity(intent);
        }

    }

    public boolean getStatus(){
        return this.isLoggedIn;
    }

    public void setStatus(boolean status){
        isLoggedIn = status;
    }

}

当用户登录时，我会在注销时将布尔isLoggedIn更改为true和false。但是当我通过成功登录并关闭它并再次启动它来检查它时，它仍然转到LoginActivity。为什么呢？

编辑：现在，我明白这是因为我在CheckLoggedIn.java的开头设置了布尔isLoggedIn到false。我怎样才能实现我想要做的事情？

编辑2：

Preference.java

public class Preference {

    Context context;
    SharedPreferences sharedPref;

    public Preference(Context context){
        this.context = context;
        sharedPref = context.getSharedPreferences("LoginState", 0);
    }

    public boolean getIsLoggedIn(){
        return sharedPref.getBoolean("State", false);
    }

    public void setIsLoggedIn(boolean state){
        SharedPreferences.Editor editor = sharedPref.edit();
        editor.putBoolean("State", state);
        editor.commit();
    }

}

MainActivity.java

public class MainActivity extends Activity {
    Preference preference = new Preference(this);
    @Override
    protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    if(preference.getIsLoggedIn()){
        Log.d("State", "Already logged in");
    }
            ......
    }
}

logcat的

02-17 16:30:53.063: E/AndroidRuntime(21450): FATAL EXCEPTION: main
02-17 16:30:53.063: E/AndroidRuntime(21450): Process: collector.lbfinance, PID: 21450
02-17 16:30:53.063: E/AndroidRuntime(21450): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{collector.lbfinance/collector.lbfinance.MainActivity}: java.lang.NullPointerException
02-17 16:30:53.063: E/AndroidRuntime(21450):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2121)
02-17 16:30:53.063: E/AndroidRuntime(21450):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
02-17 16:30:53.063: E/AndroidRuntime(21450):    at android.app.ActivityThread.access$800(ActivityThread.java:135)
02-17 16:30:53.063: E/AndroidRuntime(21450):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
02-17 16:30:53.063: E/AndroidRuntime(21450):    at android.os.Handler.dispatchMessage(Handler.java:102)
02-17 16:30:53.063: E/AndroidRuntime(21450):    at android.os.Looper.loop(Looper.java:136)
02-17 16:30:53.063: E/AndroidRuntime(21450):    at android.app.ActivityThread.main(ActivityThread.java:5017)
02-17 16:30:53.063: E/AndroidRuntime(21450):    at java.lang.reflect.Method.invokeNative(Native Method)
02-17 16:30:53.063: E/AndroidRuntime(21450):    at java.lang.reflect.Method.invoke(Method.java:515)
02-17 16:30:53.063: E/AndroidRuntime(21450):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
02-17 16:30:53.063: E/AndroidRuntime(21450):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
02-17 16:30:53.063: E/AndroidRuntime(21450):    at dalvik.system.NativeStart.main(Native Method)
02-17 16:30:53.063: E/AndroidRuntime(21450): Caused by: java.lang.NullPointerException
02-17 16:30:53.063: E/AndroidRuntime(21450):    at android.content.ContextWrapper.getSharedPreferences(ContextWrapper.java:173)
02-17 16:30:53.063: E/AndroidRuntime(21450):    at collector.lbfinance.library.Preference.<init>(Preference.java:13)
02-17 16:30:53.063: E/AndroidRuntime(21450):    at collector.lbfinance.MainActivity.<init>(MainActivity.java:52)
02-17 16:30:53.063: E/AndroidRuntime(21450):    at java.lang.Class.newInstanceImpl(Native Method)
02-17 16:30:53.063: E/AndroidRuntime(21450):    at java.lang.Class.newInstance(Class.java:1208)
02-17 16:30:53.063: E/AndroidRuntime(21450):    at android.app.Instrumentation.newActivity(Instrumentation.java:1061)
02-17 16:30:53.063: E/AndroidRuntime(21450):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2112)
02-17 16:30:53.063: E/AndroidRuntime(21450):    ... 11 more

Answer 1

为此，您必须使用shared preferences。您的布尔变量仅在您的活动未被销毁之前有效。要保留数据，您必须使用共享首选项或sqlite。

只有当我们有Relational数据库时，才会建议使用sqlite，对于应用程序seetings的轻量级持久存储等，共享首选项最好。

public class PreferenceForApp {
  Context context;
  SharedPreferences prefs;

  public PreferenceForApp(Context context) {
      this.context = context;
      prefs = context.getSharedPreferences("myAppPrefs", 0);
  }

  public Boolean getIsDeviceValidated() {

      return prefs.getBoolean("Validated", false);
  }

  public void setIsDeviceValidated(Boolean value) {

      SharedPreferences.Editor editor = prefs.edit();
      editor.putBoolean("Validated", value);
      editor.commit();
  }
}

编辑

在Activity中调用此函数并以下列方式将上下文传递给它：

PreferenceForApp myPrefs= new PreferenceForApp (this);

Boolean val=myPrefs.getIsDeviceValidated();

Answer 2

您可以使用SharedPreference存储凭据值。

在SharedPreference中存储值

SharedPreferences preferences = getSharedPreferences("userData", 0);
SharedPreferences.Editor editor = preferences.edit();
editor.putString("userName", "value");
editor.putString("password", "value");
editor.commit();

从SharedPreference中检索值

SharedPreferences preferences = getSharedPreferences("loginData", 0);
String userName = preferences.getString("userName", "");
String password = preferences.getString("password", "");

跳过活动时遇到问题

2 个答案: