Question

我正在尝试更改传感器更改的TextView内容，但在调用TextView.setText("foo");应用程序崩溃后，好像TextView变量为空。我在TextView中设置了onCreateView变量。这是代码：

public class fragment1 extends Fragment implements SensorEventListener
{
    private SensorManager mSrMgr = null;
    private Sensor mLight;
    private TextView page1;
    protected View mView;


    public fragment1()
    {
        // Required empty public constructor
    }

    public void onCreate(Bundle savedInstance)
    {
        super.onCreate(savedInstance);
        mSrMgr = (SensorManager) getActivity().getSystemService(SENSOR_SERVICE);
        mLight = mSrMgr.getDefaultSensor(Sensor.TYPE_LIGHT);
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState)
    {
        page1 = container.findViewById(R.id.page1);
        View view = inflater.inflate(R.layout.fragment_fragment1, container, false);
        this.mView = view;
        return inflater.inflate(R.layout.fragment_fragment1, container, false);
    }

    public void onPause()
    {
        super.onPause();
        this.unregister();
    }

    public void onResume()
    {
        super.onResume();
        this.registerSensorListiner();
    }

    private void registerSensorListiner()
    {
        mSrMgr.registerListener(this, mLight, SensorManager.SENSOR_DELAY_NORMAL);
    }

    private void unregister()
    {
        mSrMgr.unregisterListener(this);
    }


    @Override
    public void onSensorChanged(SensorEvent event)
    {
        Toast.makeText(getContext(),String.valueOf(event.values[0]),Toast.LENGTH_SHORT).show();
        page1.setText("elo"); //here is the crashing part
    }

    @Override
    public void onAccuracyChanged(Sensor sensor, int accuracy)
    {

    }
}

Answer 1

为什么多次 R.layout. ？

  View view = inflater.inflate(R.layout.fragment_fragment1, container, false);
        this.mView = view;
        return inflater.inflate(R.layout.fragment_fragment1, container, false);

应该是一次性的。首先修改一下。

注意

您将获得NullPointerException。

当应用程序在某个情况下尝试使用null时抛出对象是必需的。

您应该传递 View's object 。

page1 = view.findViewById(R.id.page1);

<强>最后

View view = inflater.inflate(R.layout.fragment_fragment1, container, false); page1 = view.findViewById(R.id.page1); this.mView = view; return view;

Answer 2

首先，夸大布局

View view = inflater.inflate(R.layout.fragment_fragment1, container, false);
this.mView = view;
page1 = view.findViewById(R.id.page1); 
return view, false);

使用view对象来调用findViewById方法

Answer 3

使用此

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,Bundle savedInstanceState)
{            
   View view = inflater.inflate(R.layout.fragment_fragment1, container, false);
   this.mView = view;
   page1 = view.findViewById(R.id.page1);
   return view;
}

而不是这个

@Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState)
    {
        page1 = container.findViewById(R.id.page1);
        View view = inflater.inflate(R.layout.fragment_fragment1, container, false);
        this.mView = view;
        return inflater.inflate(R.layout.fragment_fragment1, container, false);
    }

Answer 4

public class fragment1 extends Fragment implements SensorEventListener {
    private SensorManager mSrMgr = null;
    private Sensor mLight;
    private TextView page1;
    protected View mView;


    public fragment1() {
        // Required empty public constructor
    }

    public void onCreate(Bundle savedInstance) {
        super.onCreate(savedInstance);
        mSrMgr = (SensorManager) getActivity().getSystemService(SENSOR_SERVICE);
        mLight = mSrMgr.getDefaultSensor(Sensor.TYPE_LIGHT);
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {

        mView = inflater.inflate(R.layout.fragment_fragment1, container, false);
        page1 = mView.findViewById(R.id.page1);
        return mView;
    }

    public void onPause() {
        super.onPause();
        this.unregister();
    }

    public void onResume() {
        super.onResume();
        this.registerSensorListiner();
    }

    private void registerSensorListiner() {
        mSrMgr.registerListener(this, mLight, SensorManager.SENSOR_DELAY_NORMAL);
    }

    private void unregister() {
        mSrMgr.unregisterListener(this);
    }


    @Override
    public void onSensorChanged(SensorEvent event) {
        Toast.makeText(getContext(), String.valueOf(event.values[0]), Toast.LENGTH_SHORT).show();
        page1.setText("elo"); //here is the crashing part
    }

    @Override
    public void onAccuracyChanged(Sensor sensor, int accuracy) {

    }
}

Answer 5

将findViewById代码放在onActivityCreated中，如下所示：

 @Override
    public void onActivityCreated(@Nullable Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);
        page1 = getActivity().findViewById(R.id.page1);
    }

Answer 6

有时在片段中创建布局时，您将粘贴并粘贴具有重复ID的xml代码。然后，当您调用粘贴的资源的ID时，它将尝试调用第一个定义的资源，该资源在运行时可能为null。仔细检查是否仅在一个片段的Xml中找到page1 id。如果无法解决“ findviewbyid”。希望对您有所帮助，您的代码中几乎没有细节（错误消息）

片段中的TextView.setText（）崩溃应用程序

6 个答案: