Android Studio FATALE AUSNAHME: Haupt

Question

Ich bin Anfänger bei der Entwicklung von Android. Und das ist meine erste App, die ich erstellen möchte. Aber ich habe ein Problem damit und weiß nicht, wie ich es lösen soll. Bitte hilf mir. Dieser Fehler Ich habe:

03-19 14:30:44.502 22661-22661/com.don.test E/AndroidRuntime: FATAL EXCEPTION: main 
Process: com.don.test, PID: 22661 
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.don.test/com.don.test.MainActivity}: java.lang.NullPointerException 
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2224) 
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2283) 
    at android.app.ActivityThread.access$800(ActivityThread.java:144) 
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1205) 
    at android.os.Handler.dispatchMessage(Handler.java:102) 
    at android.os.Looper.loop(Looper.java:136) 
    at android.app.ActivityThread.main(ActivityThread.java:5158) 
    at java.lang.reflect.Method.invokeNative(Native Method) 
    at java.lang.reflect.Method.invoke(Method.java:515) 
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:732) 
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:566) 
    at dalvik.system.NativeStart.main(Native Method) 
Caused by: java.lang.NullPointerException 
    at com.don.test.MainActivity.onCreate(MainActivity.java:29) 
    at android.app.Activity.performCreate(Activity.java:5998) 
    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087) 
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2181) 
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2283)  
    at android.app.ActivityThread.access$800(ActivityThread.java:144)  
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1205)  
    at android.os.Handler.dispatchMessage(Handler.java:102)  
    at android.os.Looper.loop(Looper.java:136)  
    at android.app.ActivityThread.main(ActivityThread.java:5158)  
    at java.lang.reflect.Method.invokeNative(Native Method)  
    at java.lang.reflect.Method.invoke(Method.java:515)  
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:732)  
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:566)  
    at dalvik.system.NativeStart.main(Native Method)  

Das ist mein MainActivity.java

public class MainActivity extends AppCompatActivity implements View.OnClickListener{ 

Button bLogout; 
EditText etId, etNama, etUsername; 


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

    etId = (EditText) findViewById(R.id.etId); 
    etNama = (EditText) findViewById(R.id.etNama); 
    etUsername = (EditText) findViewById(R.id.etUsername); 
    bLogout = (Button) findViewById(R.id.bLogout); 

    bLogout.setOnClickListener(this); 

} 

@Override 
public void onClick(View v) { 
    switch (v.getId()){ 
     case R.id.bLogout: 


      break; 
    } 
} 
} 

ich mein Samsung Galaxy SIII Mini als Emulator verwenden. Können Sie mir mit diesem Fehler helfen, danke vor

Answer 1

Sie müssen den Inhalt Ansicht für Ihre Aktivität einstellen, bevor es die Ansichten mit:

hinzufügen

setContentView(R.layout.activity_main); // activity_main is an example, here you need to put the name of your layout 

Gleich nach

super.onCreate(savedInstanceState);