Question

Android findViewById w innej klasie przy włączaniu aplikacji wywala błąd

Błąd:

11-25 20:04:54.882 7070-7070/com.wolfriders E/AndroidRuntime: FATAL EXCEPTION: main
                                                              Process: com.wolfriders, PID: 7070
                                                              java.lang.RuntimeException: Unable to start activity ComponentInfo{com.wolfriders/com.wolfriders.Main}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.view.Window.findViewById(int)' on a null object reference
                                                                  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2817)
                                                                  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2892)
                                                                  at android.app.ActivityThread.-wrap11(Unknown Source:0)
                                                                  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1593)
                                                                  at android.os.Handler.dispatchMessage(Handler.java:105)
                                                                  at android.os.Looper.loop(Looper.java:164)
                                                                  at android.app.ActivityThread.main(ActivityThread.java:6541)
                                                                  at java.lang.reflect.Method.invoke(Native Method)
                                                                  at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240)
                                                                  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:767)
                                                               Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.view.Window.findViewById(int)' on a null object reference
                                                                  at android.app.Activity.findViewById(Activity.java:2563)
                                                                  at com.wolfriders.Login.<init>(Login.java:14)
                                                                  at com.wolfriders.Main.onCreate(Main.java:19)
                                                                  at android.app.Activity.performCreate(Activity.java:6975)
                                                                  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1213)
                                                                  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2770)
                                                                  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2892) 
                                                                  at android.app.ActivityThread.-wrap11(Unknown Source:0) 
                                                                  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1593) 
                                                                  at android.os.Handler.dispatchMessage(Handler.java:105) 
                                                                  at android.os.Looper.loop(Looper.java:164) 
                                                                  at android.app.ActivityThread.main(ActivityThread.java:6541) 
                                                                  at java.lang.reflect.Method.invoke(Native Method) 
                                                                  at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240) 
                                                                  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:767) 

 

Main:

package com.wolfriders;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;

public class Main extends AppCompatActivity {

    private boolean logged = false; // Temporary variable indicating whether you are logged in

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        if (logged == false) {
            setContentView(R.layout.login_from);

            final Login login = new Login();

            login.login_btn.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    login.loginAction();
                }

            });
        } else { setContentView(R.layout.main_activity); }
    }
}

Login:

package com.wolfriders;

import android.app.Activity;
import android.widget.Button;
import android.widget.EditText;

public class Login extends Activity {

    public EditText login_phone, login_password;
    public Button login_btn;

    Login() {
        this.login_phone = (EditText)findViewById(R.id.inputloginpassword);
        this.login_password = (EditText)findViewById(R.id.inputloginpassword);
        this.login_btn = (Button)findViewById(R.id.btnlogin);
    }

    public void loginAction() {
        // Do something after login button clicked
    }

}