Question

当我添加行list.add(sb.toString());时，程序停止工作当我删除它时，数据加载到StringBuilder，但我无法显示它我搜索了一个解决方案，但每个代码示例都是相同的我无法找到问题。

public ArrayList<String> list;
public ArrayAdapter<String> adapter;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_contact_list);

    listView = (ListView) findViewById(R.id.contactList);
    // listView.setOnItemClickListener(this);

    Cursor phones = getContentResolver().query(
            ContactsContract.CommonDataKinds.Phone.CONTENT_URI, null, null,
            null, null);
    while (phones.moveToNext()) {

        String name = phones
                .getString(phones
                        .getColumnIndex(ContactsContract.CommonDataKinds.Phone.DISPLAY_NAME));

        String phoneNumber = phones
                .getString(phones
                        .getColumnIndex(ContactsContract.CommonDataKinds.Phone.NUMBER));
        StringBuilder sb = new StringBuilder();

        sb.append(name).append(" ").append(phoneNumber);

        list.add(sb.toString());
        Log.d("Added:", sb.toString());

    }
    adapter = new ArrayAdapter<String>(this,
            android.R.layout.simple_list_item_1, list);
    listView.setAdapter(adapter);

    phones.close();

堆栈跟踪：

02-05 10:41:03.505: E/AndroidRuntime(29762): FATAL EXCEPTION: main
02-05 10:41:03.505: E/AndroidRuntime(29762): java.lang.NullPointerException
02-05 10:41:03.505: E/AndroidRuntime(29762):    at com.example.anewapp.CameraPreview.surfaceCreated(CameraPreview.java:30)
02-05 10:41:03.505: E/AndroidRuntime(29762):    at android.view.SurfaceView.updateWindow(SurfaceView.java:547)
02-05 10:41:03.505: E/AndroidRuntime(29762):    at android.view.SurfaceView.access$000(SurfaceView.java:85)
02-05 10:41:03.505: E/AndroidRuntime(29762):    at android.view.SurfaceView$3.onPreDraw(SurfaceView.java:173)
02-05 10:41:03.505: E/AndroidRuntime(29762):    at android.view.ViewTreeObserver.dispatchOnPreDraw(ViewTreeObserver.java:671)
02-05 10:41:03.505: E/AndroidRuntime(29762):    at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1821)
02-05 10:41:03.505: E/AndroidRuntime(29762):    at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:999)
02-05 10:41:03.505: E/AndroidRuntime(29762):    at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:4217)
02-05 10:41:03.505: E/AndroidRuntime(29762):    at android.view.Choreographer$CallbackRecord.run(Choreographer.java:725)
02-05 10:41:03.505: E/AndroidRuntime(29762):    at android.view.Choreographer.doCallbacks(Choreographer.java:555)
02-05 10:41:03.505: E/AndroidRuntime(29762):    at android.view.Choreographer.doFrame(Choreographer.java:525)
02-05 10:41:03.505: E/AndroidRuntime(29762):    at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:711)
02-05 10:41:03.505: E/AndroidRuntime(29762):    at android.os.Handler.handleCallback(Handler.java:615)
02-05 10:41:03.505: E/AndroidRuntime(29762):    at android.os.Handler.dispatchMessage(Handler.java:92)
02-05 10:41:03.505: E/AndroidRuntime(29762):    at android.os.Looper.loop(Looper.java:137)
02-05 10:41:03.505: E/AndroidRuntime(29762):    at android.app.ActivityThread.main(ActivityThread.java:4802)
02-05 10:41:03.505: E/AndroidRuntime(29762):    at java.lang.reflect.Method.invokeNative(Native Method)
02-05 10:41:03.505: E/AndroidRuntime(29762):    at java.lang.reflect.Method.invoke(Method.java:511)
02-05 10:41:03.505: E/AndroidRuntime(29762):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:813)
02-05 10:41:03.505: E/AndroidRuntime(29762):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:580)
02-05 10:41:03.505: E/AndroidRuntime(29762):    at dalvik.system.NativeStart.main(Native Method)

Answer 1

您需要初始化列表

list = new ArrayList<String>();

Answer 2

您显示的堆栈跟踪是针对空指针异常的。这是说你的文件CameraPreview.java的第30行取消引用空指针。

看看第30行。了解哪个指针为空以及为什么。调试代码，所以当控件在那里传递时，指针就会引用一个对象。

显然，堆栈回溯与您显示的onCreate（）没有任何关联。这对你来说是另一回事。为什么你认为它在list.add（）中失败了（或者，为什么你显示错误的堆栈追溯）？

顺便说一下，变量“list”在哪里初始化？

Android系统。当我尝试向ArrayList添加项目时，为什么会出错？

2 个答案: