Question

我有一个带有视图寻呼机和简单日期选择器的主要活动。

   public static class MyPagerAdapter extends SmartFragmentStatePagerAdapter {
    private static int NUM_ITEMS = 3;
    private List<String> titleList = Arrays.asList("Week", "Month", "Year");

    public MyPagerAdapter(FragmentManager fragmentManager) {
        super(fragmentManager);
    }

    // Returns total number of pages
    @Override
    public int getCount() {
        return NUM_ITEMS;
    }

    // Returns the fragment to display for that page
    @Override
    public Fragment getItem(int position) {
        switch (position) {
            case 0:
                return graph_week.newInstance(0, "Week");
            case 1:
                return graph_month.newInstance(1, "Month");
            case 2:
                return graph_year.newInstance(2, "Year");
            default:
                return null;
        }
    }

    // Returns the page titles
    @Override
    public CharSequence getPageTitle(int position) {
         return titleList.get(position);
    }

}

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    dateSetter = new DateSetter();
    setContentView(R.layout.activity_graph);

    ViewPager vpPager = (ViewPager) findViewById(R.id.vpPager);
    adapterViewPager = new MyPagerAdapter(getSupportFragmentManager());
    vpPager.setAdapter(adapterViewPager);
    PagerTabStrip strip = (PagerTabStrip) findViewById(R.id.pager_header);
    strip.setDrawFullUnderline(false);

    vpPager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {
        // This method will be invoked when a new page becomes selected.
        @Override
        public void onPageSelected(int position) {

        }
        // This method will be invoked when the current page is scrolled
        @Override
        public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {

        }
        // Called when the scroll state changes:
        // SCROLL_STATE_IDLE, SCROLL_STATE_DRAGGING, SCROLL_STATE_SETTLING
        @Override
        public void onPageScrollStateChanged(int state) {

        }
    });

    fragment = (graph_month) adapterViewPager.getItem(1);

    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);
}

当我选择日期时，我在我的片段中调用setCalendar来更改值。在createChart中我创建了一个简单的图表，异常在第一行出现，所以我切断了剩下的代码。

   public static graph_month newInstance(int page, String title) {
    graph_month fragment = new graph_month();
    Bundle args = new Bundle();
    args.putInt(PAGE, page);
    args.putString(TITLE, title);
    fragment.setArguments(args);
    return fragment;
}
public graph_month() {
    // Required empty public constructor
}

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    if (getArguments() != null) {
        page = getArguments().getInt(PAGE);
        title = getArguments().getString(TITLE);
    }
}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    View view = inflater.inflate(R.layout.fragment_graph_month, container, false);

    return view;
}

@Override
public void onViewCreated(View view, Bundle savedInstanceState) {
    super.onViewCreated(view, savedInstanceState);
  this.createChart();
}

@Override
public void onAttach(Context context) {
    super.onAttach(context);
}

@Override
public void onDetach() {
    super.onDetach();
    mListener = null;
}


public void setCalendar(Calendar cal) {
    this.cal = cal;
    maxMonth = cal.getActualMaximum(cal.DAY_OF_MONTH);
    this.createChart();
}

public void createChart() {
    lineChartW= (LineChart) getView().findViewById(R.id.lineChartW);

但现在我在null对象引用上得到一个NullPointerException，而我的视图现在为null。我不知道为什么，我想不出任何其他方式来更新我的活动中的片段。

完整错误代码：

处理：com.example.snyap.graphdemo，PID：1491 java.lang.NullPointerException：尝试在空对象引用上调用虚方法'java.lang.String android.view.View.toString（）' 在com.example.snyap.graphdemo.graphs.graph_month.createChart（graph_month.java:125）在com.example.snyap.graphdemo.graphs.graph_month.setCalendar（graph_month.java:120）在com.example.snyap.graphdemo.Graph.setDate（Graph.java:138）在com.example.snyap.graphdemo.Graph.onDateSet（Graph.java:144）在android.app.DatePickerDialog.onClick（DatePickerDialog.java:134）在com.android.internal.app.AlertController $ ButtonHandler.handleMessage（AlertController.java:165）在android.os.Handler.dispatchMessage（Handler.java:111）在android.os.Looper.loop（Looper.java:194）在android.app.ActivityThread.main（ActivityThread.java:5549） 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:964）在com.android.internal.os.ZygoteInit.main（ZygoteInit.java:759）

Answer 1

这是一种正确的方法：

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    View view = inflater.inflate(R.layout.fragment_graph_month, container, false);
    lineChartW= (LineChart) view.findViewById(R.id.lineChartW);
    return view;
}

没有必要覆盖onViewCreated这样的事情。您可以在充气后访问该视图。您可以阅读更多关于此here的内容。

Android：更新片段

1 个答案: