无法调用意图

Question

我尝试从其他活动中调用此活动，但是应用程序强制退出。 这是我的代码。

public class Records extends Activity {

// Array of strings storing country names
String[] types = new String[] {
    "Tutorial Room",
    "Lecture Hall",
    "Tutorial Room",
    "Tutorial Room"
};

// Array of integers points to images stored in /res/drawable-ldpi/
int[] icon = new int[]{
    R.drawable.tutorialroom,
    R.drawable.lecturehall,
    R.drawable.tutorialroom,
    R.drawable.tutorialroom
};

// Array of strings to store currencies
String[] info = new String[]{
    "Booking1",
    "Booking2",
    "Booking3",
    "Booking4"
};

/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);

    // Each row in the list stores country name, currency and flag
    List<HashMap<String,String>> aList = new ArrayList<HashMap<String,String>>();

    for(int i=0;i<4;i++){
        HashMap<String, String> hm = new HashMap<String,String>();
        hm.put("txt", "Name : " + types[i]);
        hm.put("cur","Type : " + info[i]);
        hm.put("flag", Integer.toString(icon[i]) );
        aList.add(hm);
    }

    // Keys used in Hashmap
    String[] from = { "flag","txt","cur" };

    // Ids of views in listview_layout
    int[] to = { R.id.flag,R.id.txt,R.id.cur};

    // Instantiating an adapter to store each items
    // R.layout.listview_layout defines the layout of each item
    SimpleAdapter adapter = new SimpleAdapter(getBaseContext(), aList, R.layout.listview_layout, from, to);

    // Getting a reference to listview of main.xml layout file
    ListView listView = ( ListView ) findViewById(R.id.listview);

    // Setting the adapter to the listView
    listView.setAdapter(adapter);


}

08-23 12:19:50.449: E/AndroidRuntime(7642): 致命异常: main 08-23 12:19:50.449: E/AndroidRuntime(7642): 进程: my.edu.utar.sofebos, PID: 7642 08-23 12:19:50.449: E/AndroidRuntime(7642): java.lang.RuntimeException: 无法启动活动 ComponentInfo{my.edu.utar.sofebos/my.edu.utar.sofebos.Records}: java.lang 。空指针异常 08-23 12:19:50.449: E/AndroidRuntime(7642): 在 android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2195) 08-23 12:19:50.449: E/AndroidRuntime(7642): 在 android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245) 08-23 12:19:50.449: E/AndroidRuntime(7642): 在 android.app.ActivityThread.access$800(ActivityThread.java:135) 08-23 12:19:50.449: E/AndroidRuntime(7642): 在 android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196) 08-23 12:19:50.449: E/AndroidRuntime(7642): 在 android.os.Handler.dispatchMessage(Handler.java:102) 08-23 12:19:50.449: E/AndroidRuntime(7642): 在 android.os.Looper.loop(Looper.java:136) 08-23 12:19:50.449: E/AndroidRuntime(7642): 在 android.app.ActivityThread.main(ActivityThread.java:5017) 08-23 12:19:50.449: E/AndroidRuntime(7642): 在 java.lang.reflect.Method.invokeNative(Native Method) 08-23 12:19:50.449: E/AndroidRuntime(7642): 在 java.lang.reflect.Method.invoke(Method.java:515) 08-23 12:19:50.449: E/AndroidRuntime(7642): 在 com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779) 08-23 12:19:50.449: E/AndroidRuntime(7642): 在 com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595) 08-23 12:19:50.449: E/AndroidRuntime(7642): 在 dalvik.system.NativeStart.main(Native Method) 08-23 12:19:50.449: E/AndroidRuntime(7642): 引起: java.lang.NullPointerException 08-23 12:19:50.449: E/AndroidRuntime(7642): 在 my.edu.utar.sofebos.Records.onCreate(Records.java:71) 08-23 12:19:50.449: E/AndroidRuntime(7642): 在 android.app.Activity.performCreate(Activity.java:5231) 08-23 12:19:50.449: E/AndroidRuntime(7642): 在 android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087) 08-23 12:19:50.449: E/AndroidRuntime(7642): 在 android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2159) 08-23 12:19:50.449: E/AndroidRuntime(7642): ... 11 更多

Answer 1

由于您在以下几行中收到java.lang.NullPointerException：

ListView listView = ( ListView ) findViewById(R.id.listview);
listView.setAdapter(adapter);

1. 您需要检查main.xml 的ID listview。确保 它存在。
2. 确保您使用了正确的布局setContentView()

Answer 2

您是否正在尝试调用您想要的意图？

这是制作电话意图的代码：

Intent callIntent = new Intent(Intent.ACTION_CALL);
    callIntent.setData(Uri.parse("tel:" + phone));
    startActivity(callIntent);

并在您的清单文件中添加这样的权限：

<uses-permission android:name="android.permission.CALL_PHONE" />