Android：打開列表查看活動

Question

我嘗試使用可能不同的方式打開我的listView活動，這些方法可以在Google搜索時從Android Dev Resources找到。每次它不起作用，並給我錯誤。

我試圖打開一個新的活動與列表，當我點擊一個按鈕從主要活動。

我今天剛剛開始用Android編程，所以詳細的解釋會對我有很大的幫助。

我想我已經把問題指向了JokesActivity.java（下） 如果我需要從我的程序發佈更多的文件，請評論，我會發布它們。

JokesActivity：

public class JokesActivity extends Activity { 
    @Override 
    public void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 

     ListView listView = (ListView) findViewById(R.id.mylist); 

     ArrayAdapter<String> adapter = new ArrayAdapter<String>(this, 
       android.R.layout.simple_list_item_1, android.R.id.text1, CATEGORIES); 

     listView.setAdapter(adapter); 
    } 

    String[] CATEGORIES = new String[] { 
      "Blonde", "Chuck Norris" 
    }; 
} 

logcat的：

05-26 11:19:51.236: D/AndroidRuntime(12173): Shutting down VM 
05-26 11:19:51.236: W/dalvikvm(12173): threadid=1: thread exiting with uncaught exception (group=0x40018560) 
05-26 11:19:51.236: E/AndroidRuntime(12173): FATAL EXCEPTION: main 
05-26 11:19:51.236: E/AndroidRuntime(12173): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.lulzone/com.lulzone.JokesActivity}: java.lang.NullPointerException 
05-26 11:19:51.236: E/AndroidRuntime(12173): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1696) 
05-26 11:19:51.236: E/AndroidRuntime(12173): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1716) 
05-26 11:19:51.236: E/AndroidRuntime(12173): at android.app.ActivityThread.access$1500(ActivityThread.java:124) 
05-26 11:19:51.236: E/AndroidRuntime(12173): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:968) 
05-26 11:19:51.236: E/AndroidRuntime(12173): at android.os.Handler.dispatchMessage(Handler.java:99) 
05-26 11:19:51.236: E/AndroidRuntime(12173): at android.os.Looper.loop(Looper.java:130) 
05-26 11:19:51.236: E/AndroidRuntime(12173): at android.app.ActivityThread.main(ActivityThread.java:3806) 
05-26 11:19:51.236: E/AndroidRuntime(12173): at java.lang.reflect.Method.invokeNative(Native Method) 
05-26 11:19:51.236: E/AndroidRuntime(12173): at java.lang.reflect.Method.invoke(Method.java:507) 
05-26 11:19:51.236: E/AndroidRuntime(12173): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839) 
05-26 11:19:51.236: E/AndroidRuntime(12173): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597) 
05-26 11:19:51.236: E/AndroidRuntime(12173): at dalvik.system.NativeStart.main(Native Method) 
05-26 11:19:51.236: E/AndroidRuntime(12173): Caused by: java.lang.NullPointerException 
05-26 11:19:51.236: E/AndroidRuntime(12173): at com.lulzone.JokesActivity.onCreate(JokesActivity.java:19) 
05-26 11:19:51.236: E/AndroidRuntime(12173): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047) 
05-26 11:19:51.236: E/AndroidRuntime(12173): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1660) 
05-26 11:19:51.236: E/AndroidRuntime(12173): ... 11 more 

list_item.xml

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

    <ListView 
     android:id="@+id/mylist" 
     android:layout_width="fill_parent" 
     android:layout_height="wrap_content" > 
    </ListView> 

</LinearLayout> 

main.xml中

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

    <LinearLayout 
     android:layout_weight="1.00" 
     android:layout_width="0dp" 
     android:layout_height="fill_parent" 
     android:orientation="vertical" > 

    <Button 
     android:id="@+id/button1" 
     android:layout_width="fill_parent" 
     android:layout_height="wrap_content" 
     android:layout_weight="1.00" 
     android:text="@string/button_jokes" 
     android:onClick="openJokes"/> 

    <Button 
     android:id="@+id/button2" 
     android:layout_width="fill_parent" 
     android:layout_height="wrap_content" 
     android:layout_weight="1.00" 
     android:text="@string/button_facts" /> 

</LinearLayout> 

<LinearLayout 
    android:layout_weight="1.00" 
    android:layout_width="0dp" 
    android:layout_height="fill_parent" 
    android:orientation="vertical" > 

    <Button 
     android:id="@+id/button3" 
     android:layout_width="fill_parent" 
     android:layout_height="wrap_content" 
     android:layout_weight="1.00" 
     android:text="@string/button_quotes" /> 

    <Button 
     android:id="@+id/button4" 
     android:layout_width="fill_parent" 
     android:layout_height="wrap_content" 
     android:layout_weight="1.00" 
     android:text="@string/button_more" /> 

</LinearLayout> 

Answer 1

你應該main.xml中添加setContentView(R.layout.main) first

setContentView(R.layout.main); 
ListView listView = (ListView) findViewById(R.id.mylist); 

UPDATE

放列表視圖

<ListView 
     android:id="@+id/mylist" 
     android:layout_width="fill_parent" 
     android:layout_height="wrap_content" > 
    </ListView>