Question

我正在尝试点击片段中的按钮。就像在下面的过程中一样：

点击片段导航抽屉中的A
App open up Fragment A
当片段A启动时，它会在其类中的按钮上执行Click（），这将导致活动B

我已经尝试将btnSchedule.performClick();放在OnCreate，OnStart甚至是AsyncTask onPostExecute方法中。

然而，这一切都会导致nullpointerException，如下所示：

02-25 16：03：13.421 17348-17348 / com.example.l33902.contactmanagment1512 E / AndroidRuntime：致命异常：主要处理：com.example.l33902.contactmanagment1512，PID：17348 java.lang.NullPointerException：尝试调用虚方法空对象上的'boolean android.widget.Button.performClick（）' 参考在 com.example.l33902.contactmanagment.FragmentPlanner.onStart（FragmentPlanner.java:106）在android.app.Fragment.performStart（Fragment.java:2138）在 android.app.FragmentManagerImpl.moveToState（FragmentManager.java:937）在 android.app.FragmentManagerImpl.moveToState（FragmentManager.java:1082）在android.app.BackStackRecord.run（BackStackRecord.java:834）在 android.app.FragmentManagerImpl.execPendingActions（FragmentManager.java:1467）在android.app.FragmentManagerImpl $ 1.run（FragmentManager.java:452）在android.os.Handler.handleCallback（Handler.java:739）在android.os.Handler.dispatchMessage（Handler.java:95）在android.os.Looper.loop（Looper.java:145）在android.app.ActivityThread.main（ActivityThread.java:6897） at java.lang.reflect.Method.invoke（Native Method）在java.lang.reflect.Method.invoke（Method.java:372）在 com.android.internal.os.ZygoteInit $ MethodAndArgsCaller.run（ZygoteInit.java:1404）在com.android.internal.os.ZygoteInit.main（ZygoteInit.java:1199）

以下是我的代码（片段A）（目前在onStart方法中放置btnSchedule.performClick();）：

public class FragmentPlanner extends Fragment {

    View root;
    Context context;
    Button btnSchedule;

    public FragmentPlanner() {
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        final View rootView = inflater.inflate(R.layout.fragment_planner, container, false);
        root = rootView;
        context = rootView.getContext();
        setHasOptionsMenu(true);

        Button btnSchedule = (Button)rootView.findViewById(R.id.btnSchedule);
        btnSchedule.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                // here you set what you want to do when user clicks your button,

                Intent intent = new Intent(getActivity(), CalendarMain.class);
                startActivity(intent);

            }
        });



        return rootView;
    }

    @Override
    public void onCreateOptionsMenu(Menu menu, MenuInflater inflater) {
        inflater.inflate(R.menu.to_note, menu);
        MenuItem noteItem;
        noteItem = menu.findItem(R.id.action_note).setIcon(resizeImage(R.drawable.ic_note_add_white_24dp, 250, 250));
        noteItem.setVisible(true);

    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        int id = item.getItemId();
        if(id == R.id.action_note){
            //Do whatever you want to do

            Intent intent = new Intent(context, CalendarMain.class);
            startActivity(intent);

            return true;
        }

        return super.onOptionsItemSelected(item);
    }

    private Drawable resizeImage(int resId, int w, int h) {
        Bitmap BitmapOrg = BitmapFactory.decodeResource(getResources(), resId);
        int width = BitmapOrg.getWidth();
        int height = BitmapOrg.getHeight();
        int newWidth = w;
        int newHeight = h;
        float scaleWidth = ((float) newWidth) / width;
        float scaleHeight = ((float) newHeight) / height;
        Matrix matrix = new Matrix();
        matrix.postScale(scaleWidth, scaleHeight);
        Bitmap resizedBitmap = Bitmap.createBitmap(BitmapOrg, 0, 0, width, height, matrix, true);
        return new BitmapDrawable(resizedBitmap);
    }

    @Override
    public void onStart(){
        super.onStart();

        btnSchedule.performClick();

        }


}

Answer 1

这一行错了：

Button btnSchedule = (Button)rootView.findViewById(R.id.btnSchedule);

必须是：

btnSchedule = (Button)rootView.findViewById(R.id.btnSchedule);

因为有一个成员：

Button btnSchedule;

当你写：

Button btnSchedule = (Button)rootView.findViewById(R.id.btnSchedule);

您正在声明一个局部变量，而不是指定一个成员。

Answer 2

在onCreateView中，您正在重新定义本地范围内的成员btnSchedule，隐藏未初始化的类成员。在onCreateView中更改

Button btnSchedule = (Button)rootView.findViewById(R.id.btnSchedule);

与

btnSchedule = (Button)rootView.findViewById(R.id.btnSchedule);

Answer 3

像这样修改代码：

public class FragmentPlanner extends Fragment {

    View rootView;
    Context context;
    Button btnSchedule;

    public FragmentPlanner() {
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        rootView = inflater.inflate(R.layout.fragment_planner, container, false);
        context = rootView.getContext();
        setHasOptionsMenu(true);
        btnSchedule = (Button)rootView.findViewById(R.id.btnSchedule);
        btnSchedule.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                // here you set what you want to do when user clicks your button,
                Intent intent = new Intent(getActivity(), CalendarMain.class);
                startActivity(intent);
            }
        });
        return rootView;
    }

希望它有所帮助!!!

performClick（）

3 个答案: