跳过活动时遇到问题

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，我在注销时将布尔值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？

编辑：现在，我明白这是因为我在CheckLoggedIn.java的开头将布尔值isLoggedIn设置为false 。 我怎样才能实现我想做的事情？

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.(Preference.java:13) 02-17 16:30:53.063: E/AndroidRuntime(21450): at collector.lbfinance.MainActivity.(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

您必须为此目的使用共享首选项 。 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，共享首选项是最好的。

 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

在您的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存储凭据的值。

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(); 

要从SharedPreference中检索值，

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