如何在使用if else的佈局之間進行選擇？

Question

我試圖根據if else語句在兩個佈局之間切換。我不知道我出錯的地方。任何人都請幫忙。

public class MainActivity extends Activity 
{ 
    TextView head, tname, tid, tphone; 
    EditText ename, eid, ephone; 
    Button submit; 
    List label = new ArrayList<String>(); 
    List labels = new ArrayList<String>(); 
    String name, id, phone; 

    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     DataBaseHelper db = new DataBaseHelper(getApplicationContext()); 
     labels = db.getAllLabels(); 

     if (labels.isEmpty()) { 
      setContentView(R.layout.activity_main); 
      System.out.println("in if loop"); 
     } else { 
      System.out.println("in else loop");  
      Intent i = new Intent(this, activity2.class); 
      startActivity(i); 
      MainActivity.this.finish(); 
     } 

     System.out.println("Coming into onCreate");      
     Calendar cal = Calendar.getInstance(); 
     cal.setTimeInMillis(System.currentTimeMillis()); 

     cal.add(Calendar.DAY_OF_MONTH, 1); 
     cal.set(Calendar.HOUR_OF_DAY, 10); 
     cal.set(Calendar.MINUTE, 00); 
     cal.set(Calendar.SECOND, 10); 
     System.out.println(cal.toString() + "   " + cal.getTime()); 

     Intent intent = new Intent(MainActivity.this, TestService.class); 

     PendingIntent pintent = PendingIntent.getService(this, 0, intent, 0); 

     AlarmManager alarm = (AlarmManager) getSystemService(Context.ALARM_SERVICE); 
     // int i; 
     // i=24*60*60*1000; 
     alarm.setRepeating(AlarmManager.RTC_WAKEUP, cal.getTimeInMillis(), 
        86400000, pintent); 

     head = (TextView) findViewById(R.id.textView1); 
     tname = (TextView) findViewById(R.id.textView2); 
     tid = (TextView) findViewById(R.id.textView3); 
     tphone = (TextView) findViewById(R.id.textView4); 
     ename = (EditText) findViewById(R.id.editText1); 
     eid = (EditText) findViewById(R.id.editText2); 
     ephone = (EditText) findViewById(R.id.editText3); 
     submit = (Button) findViewById(R.id.button1); 

     // head.setText("REGISTER"); 
     // tname.setText("NAME:"); 
     // tid.setText("ID:"); 
     // tphone.setText("PHONE NUMBER"); 

     submit.setOnClickListener(new OnClickListener() { 

      @Override 
      public void onClick(View v) { 
       // TODO Auto-generated method stub 

       name = ename.getText().toString(); 
       id = eid.getText().toString(); 
       phone = ephone.getText().toString(); 

       label.add(name); 
       label.add(id); 
       label.add(phone); 

       DataBaseHelper db = new DataBaseHelper(getApplicationContext()); 
       // labels=db.getAllLabels(); 
       db.insertLabel(label); 
       Toast.makeText(getApplicationContext(), "Registered", 
          Toast.LENGTH_SHORT).show(); 
       MainActivity.this.finish(); 
      } 
     }); 

    } 

} 

錯誤的logcat：

12-16 15:09:18.452: E/AndroidRuntime(9117): FATAL EXCEPTION: main 
12-16 15:09:18.452: E/AndroidRuntime(9117): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.alarmservice/com.example.alarmservice.MainActivity}: java.lang.NullPointerException 
12-16 15:09:18.452: E/AndroidRuntime(9117):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2114) 
12-16 15:09:18.452: E/AndroidRuntime(9117):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2139) 
12-16 15:09:18.452: E/AndroidRuntime(9117):  at android.app.ActivityThread.access$700(ActivityThread.java:143) 
12-16 15:09:18.452: E/AndroidRuntime(9117):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1241) 
12-16 15:09:18.452: E/AndroidRuntime(9117):  at android.os.Handler.dispatchMessage(Handler.java:99) 
12-16 15:09:18.452: E/AndroidRuntime(9117):  at android.os.Looper.loop(Looper.java:137) 
12-16 15:09:18.452: E/AndroidRuntime(9117):  at android.app.ActivityThread.main(ActivityThread.java:4960) 
12-16 15:09:18.452: E/AndroidRuntime(9117):  at java.lang.reflect.Method.invokeNative(Native Method) 
12-16 15:09:18.452: E/AndroidRuntime(9117):  at java.lang.reflect.Method.invoke(Method.java:511) 
12-16 15:09:18.452: E/AndroidRuntime(9117):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1038) 
12-16 15:09:18.452: E/AndroidRuntime(9117):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:805) 
12-16 15:09:18.452: E/AndroidRuntime(9117):  at dalvik.system.NativeStart.main(Native Method) 
12-16 15:09:18.452: E/AndroidRuntime(9117): Caused by: java.lang.NullPointerException 
12-16 15:09:18.452: E/AndroidRuntime(9117):  at com.example.alarmservice.MainActivity.onCreate(MainActivity.java:110) 
12-16 15:09:18.452: E/AndroidRuntime(9117):  at android.app.Activity.performCreate(Activity.java:5203) 
12-16 15:09:18.452: E/AndroidRuntime(9117):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1094) 
12-16 15:09:18.452: E/AndroidRuntime(9117):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2078) 
12-16 15:09:18.452: E/AndroidRuntime(9117):  ... 11 more 

Answer 1

添加return;聲明MainActivity.this.finish();

Answer 2

後

調整你的if語句，然後將代碼的其餘部分在整個街區：

if (!labels.isEmpty()) { 
    System.out.println("in else loop");  
    Intent i = new Intent(this, activity2.class); 
    startActivity(i); 
    MainActivity.this.finish(); 
} 
else { 
    setContentView(R.layout.activity_main); 
    System.out.println("in if loop"); 
    System.out.println("Coming into onCreate");      
    Calendar cal = Calendar.getInstance(); 
    cal.setTimeInMillis(System.currentTimeMillis()); 

    cal.add(Calendar.DAY_OF_MONTH, 1); 
    cal.set(Calendar.HOUR_OF_DAY, 10); 
    cal.set(Calendar.MINUTE, 00); 
    cal.set(Calendar.SECOND, 10); 

    //and the rest of the code 
}