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登录(除非他们从仪表板注销)。因此,我创建了一个类来检查用户是否登录
检查登录.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,我更改布尔值isLoggedIn
to true
and false
当注销时。但是当我通过登录成功并关闭它并再次启动来检查它时,它仍然转到LoginActivity。为什么?
编辑:现在,我明白这是因为我设置了布尔值isLoggedIn
to false
在 CheckLoggedIn.java 的开头。我怎样才能实现我想要做的事情?
编辑2:
偏好设置.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
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