TextView.setText() 在片段中使应用程序崩溃

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，就好像 TextView 变量为空一样。我在 onCreateView 中设置了 TextView 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

使用这个

@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 2

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。首先修改这里。

备注

你会得到NullPointerException.

Thrown when an application attempts to use null in a case where an object is required.

你应该通过 View's object .

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

终于

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

Answer 3

首先，给布局充气

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对象调用findViewById方法

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

将您的 findViewById 代码放入 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，您会复制并粘贴具有重复 ID 的 xml 代码。当您随后调用粘贴资源的 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 page1 id 是否仅在一个片段的 Xml 中找到。如果不能解决 "findviewbyid"。希望对您有所帮助，您的代码中没有详细信息（错误消息）

TextView.setText() 在片段中使应用程序崩溃

TextView.setText() in fragment crashes app

crash

android

fragment

sensors