Android - 버튼을 동적으로 추가 - 오류 발생

Question

XML로 디자인 된 레이아웃이 있습니다. 그런 다음 자바 프로그래밍에 의해 버튼을 추가하고 싶습니다. marginparam, layoutparams를 어떻게 사용하든 관계없이 addview를 할 때마다 항상 오류가 발생합니다.

내가 뭘 잘못하고 있니? 없어진 물건 있어요?

또한 MarginLayoutParams 내의 RelativeLayout.LayoutParams.FILL_PARENT가 사용되지 않는다는 경고가 나타납니다. 그래서 이것을하는 다른 방법은 무엇입니까? 새 단추를 상대 레이아웃의 특정 위치에 놓으려고합니다.

감사합니다, AJ

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

    Button btn = new Button(this); 
    btn.setText("Go!"); 
    btn.setOnClickListener(new Button.OnClickListener() { 
     public void onClick(View v) { 
      number_of_cards=0; 
     } 
    });  


    RelativeLayout ll = (RelativeLayout) findViewById(R.layout.activity_main); 

    //ll.addView(btn); 
    //setContentView(ll); 

    float density = getApplicationContext().getResources().getDisplayMetrics().density; 
    MarginLayoutParams marginParams; 
    RelativeLayout.LayoutParams layoutParams; 

    int px_left = Math.round((float) (30+(4-1)*75) * density); 
    int px_top = Math.round((float) (30+(1-1)*91) * density); 
    marginParams = new MarginLayoutParams(RelativeLayout.LayoutParams.FILL_PARENT,RelativeLayout.LayoutParams.FILL_PARENT); 
    marginParams.setMargins(px_left, px_top, 0, 0); 
    layoutParams = new RelativeLayout.LayoutParams(marginParams); 
    btn.setLayoutParams(layoutParams);    
    ll.addView(btn, layoutParams); // getting error here 
    setContentView(R.layout.activity_main); 

로그 캣은 다음과 같습니다

12-07 10:57:03.534: E/AndroidRuntime(850): FATAL EXCEPTION: main 

12-07 10:57:03.534: E/AndroidRuntime(850): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.first/com.example.first.First}: java.lang.NullPointerException 

12-07 10:57:03.534: E/AndroidRuntime(850): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1647) 

12-07 10:57:03.534: E/AndroidRuntime(850): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1663) 

12-07 10:57:03.534: E/AndroidRuntime(850): at android.app.ActivityThread.access$1500(ActivityThread.java:117) 

12-07 10:57:03.534: E/AndroidRuntime(850): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:931) 

12-07 10:57:03.534: E/AndroidRuntime(850): at android.os.Handler.dispatchMessage(Handler.java:99) 

12-07 10:57:03.534: E/AndroidRuntime(850): at android.os.Looper.loop(Looper.java:123) 

12-07 10:57:03.534: E/AndroidRuntime(850): at android.app.ActivityThread.main(ActivityThread.java:3683) 

12-07 10:57:03.534: E/AndroidRuntime(850): at java.lang.reflect.Method.invokeNative(Native Method) 

12-07 10:57:03.534: E/AndroidRuntime(850): at java.lang.reflect.Method.invoke(Method.java:507) 

12-07 10:57:03.534: E/AndroidRuntime(850): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839) 

12-07 10:57:03.534: E/AndroidRuntime(850): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597) 

12-07 10:57:03.534: E/AndroidRuntime(850): at dalvik.system.NativeStart.main(Native Method) 

12-07 10:57:03.534: E/AndroidRuntime(850): Caused by: java.lang.NullPointerException 

12-07 10:57:03.534: E/AndroidRuntime(850): at com.example.first.First.onCreate(First.java:127) 

12-07 10:57:03.534: E/AndroidRuntime(850): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047) 

12-07 10:57:03.534: E/AndroidRuntime(850): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1611) 

12-07 10:57:03.534: E/AndroidRuntime(850): ... 11 more 

내 activity_main의 XML은 다음과 같습니다 :

<?xml version="1.0" encoding="utf-8"?> 
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" 
xmlns:tools="http://schemas.android.com/tools" 
android:layout_width="fill_parent" 
android:layout_height="fill_parent" 
android:orientation="vertical" > 

<TextView 
    android:id="@+id/textScore" 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:layout_alignParentLeft="true" 
    android:layout_alignParentTop="true" 
    android:layout_marginLeft="30dp" 
    android:layout_marginTop="5dp" 
    android:text="@string/text_score" /> 

</RelativeLayout> 

Answer 1

.. 아래의 확인 : - 라인 아래 쓰기

setContentView(R.layout.activity_main); 

super.onCreate(savedInstanceState); 

후를 그리고 라인

아래 쓰기 0 대신

RelativeLayout ll = (RelativeLayout) findViewById(R.layout.activity_main); 

그리고 코드 아래 사용하여 XML을 업데이트의

RelativeLayout ll = (RelativeLayout) findViewById(R.id.mRlayout1); 

.

<?xml version="1.0" encoding="utf-8"?> 
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" 
xmlns:tools="http://schemas.android.com/tools" 
android:layout_width="fill_parent" 
android:layout_height="fill_parent" 
android:id="@+id/mRlayout1"> 

<TextView 
    android:id="@+id/textScore" 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:layout_alignParentLeft="true" 
    android:layout_alignParentTop="true" 
    android:layout_marginLeft="30dp" 
    android:layout_marginTop="5dp" 
    android:text="@string/text_score" /> 

</RelativeLayout> 

마지막으로 제거하면 문제가 해결됩니다.

Answer 2

당신은 findViewById를 호출하기 전에 setContentView를 호출해야 .. 마가미를 설정하고 N 그것은 당신에게

솔루션은 NullPointerException이 제공

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

setContentView(R.layout.activity_main); 

Button btn = new Button(this); 
btn.setText("Go!"); 
btn.setOnClickListener(new Button.OnClickListener() { 
    public void onClick(View v) { 
     number_of_cards=0; 
    } 
});  


RelativeLayout ll = (RelativeLayout) findViewById(R.layout.activity_main); 

//ll.addView(btn); 
//setContentView(ll); 

float density = getApplicationContext().getResources().getDisplayMetrics().density; 
MarginLayoutParams marginParams; 
RelativeLayout.LayoutParams layoutParams; 

int px_left = Math.round((float) (30+(4-1)*75) * density); 
int px_top = Math.round((float) (30+(1-1)*91) * density); 

layoutParams = new RelativeLayout.LayoutParams(RelativeLayout.LayoutParams.FILL_PARENT,RelativeLayout.LayoutParams.FILL_PARENT); 
layoutParams.setMargins(px_left, px_top, 0, 0); 
btn.setLayoutParams(layoutParams);    
ll.addView(btn, layoutParams); // getting error here 

Answer 3

이 줄을 제거해보십시오 ... btn.setLayoutParams (layoutParams);

에 레이아웃 매개 변수를 제공 할 때 ll.addView (btn, layoutParams);