Android - 動態添加按鈕 - 出錯

我有一個由XML設計的佈局。然後，我想通過Java編程添加一個按鈕。無論我如何使用marginparams，layoutparams，我在執行addview時總會遇到錯誤。Android - 動態添加按鈕 - 出錯

我在做什麼錯？什麼不見了？

此外，我收到了一個警告，即MarginLayoutParams中的RelativeLayout.LayoutParams.FILL_PARENT已被棄用。那麼做什麼是另一種方式呢？我想把新按鈕放在相對佈局的特定位置。

感謝， 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);

的logcat的是：

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

我activity_main XML如下：

<?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>

來源

2012-12-07 AJ Gottes

請出示一些logcat的爲你得到 – Stupidus

喜Stupidus錯誤。它給出：NullPointerException。 –

用LogCat編輯我的問題 –

它給你NullPointerException異常

解決方案是： - 下面寫一行

setContentView(R.layout.activity_main);

後

super.onCreate(savedInstanceState);

而下面寫一行

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

代替

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

而且使用下面的代碼更新XML。

<?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>

並從上次刪除，它將解決您的問題。

來源

2012-12-07 10:32:07

Dipak Keshariya，它不能解決問題。 :-(我仍然得到NullPointerException ... –

Dipak，我如何獲得佈局ID？它不會出現在R.id. autocompletion列表中... –

我添加了xml代碼 –

你需要調用findViewById之前調用setContentView .. 並設置margi n檢查下面..

@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

來源

2012-12-07 10:31:30 Nermeen

我仍然收到NullPointerException ... –

嘗試刪除此行... btn.setLayoutParams（layoutParams）;

當您在中提供佈局參數ll.addView（btn，layoutParams）;

問候，\ n 網速慢

來源

2013-01-18 05:14:33 Suman

Android - 動態添加按鈕 - 出錯

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