java - 添加 EditText 时 Fragment 中出现 NullPointerException

Question

我正在使用选项卡式布局，使用向导创建，并准备好一个 fragment 。我已经向我的 fragment 添加了一些 EditText，并且一切准备就绪，但是，在运行应用程序时，我在 EditText 声明处收到 NullPointerException。

fragment 代码:

package com.boreas.snowdaycalculatorsp2;

import android.content.Context;
import android.support.v4.app.Fragment;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;

public class AdvancedFragment extends Fragment {
    EditText inSnow, durnStorm, pSnow, pTime, fSnow, wSpeed, sGround;
    public double inchSnow, durationStorm, peakSnow, peakTime, finalSnow, windSpeed, snowGround, result;
    TextView results;
    Button calc;
    String resInt;
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        inSnow = (EditText) getView().findViewById(R.id.inchesSnow);
        durnStorm = (EditText)getView().findViewById(R.id.durationStorm);
        pSnow = (EditText) getView().findViewById(R.id.peakRate);
        pTime = (EditText)getView().findViewById(R.id.peakRateTime);
        fSnow = (EditText) getView().findViewById(R.id.finalRate);
        wSpeed = (EditText) getView().findViewById(R.id.windSpeed);
        sGround = (EditText) getView().findViewById(R.id.snowGround);
        results = (TextView) getView().findViewById(R.id.resultView);
        calc = (Button) getView().findViewById(R.id.button);

        return inflater.inflate(R.layout.advfrag_layout, container, false);




    }

}

XML fragment :

<?xml version="1.0" encoding="utf-8"?>

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical" android:layout_width="match_parent"
    android:background="#000000"
    android:layout_height="match_parent">

    <EditText
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:inputType="numberDecimal"
        android:ems="10"
        android:id="@+id/inchesSnow"
        android:layout_alignParentTop="true"
        android:layout_alignParentLeft="true"
        android:layout_alignParentRight="true"
        android:textColor="#ffffff"
        android:textColorHint="#ffffff"
        android:hint="Inches of Snow"
        android:singleLine="true" />

    <EditText
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:inputType="numberDecimal"
        android:ems="10"
        android:id="@+id/durationStorm"
        android:layout_below="@+id/inchesSnow"
        android:layout_alignParentLeft="true"
        android:layout_alignParentRight="true"
        android:textColor="#ffffff"
        android:textColorHint="#ffffff"
        android:hint="Duration of Storm"
        android:singleLine="true" />

    <EditText
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:inputType="numberDecimal"
        android:ems="10"
        android:id="@+id/peakRate"
        android:layout_below="@+id/durationStorm"
        android:layout_alignParentLeft="true"
        android:layout_alignParentRight="true"
        android:hint="Peak Snow Rate"
        android:textColor="#ffffff"
        android:textColorHint="#ffffff"
        android:layout_alignParentStart="false"
        android:singleLine="true" />

    <EditText
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:inputType="numberDecimal"
        android:ems="10"
        android:id="@+id/peakRateTime"
        android:layout_below="@+id/peakRate"
        android:layout_alignParentLeft="true"
        android:layout_alignParentRight="true"
        android:hint="Time of Peak Snow Rate"
        android:textColor="#ffffff"
        android:textColorHint="#ffffff"
        android:singleLine="true" />

    <EditText
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:inputType="numberSigned"
        android:ems="10"
        android:id="@+id/finalRate"
        android:layout_below="@+id/peakRateTime"
        android:layout_alignParentLeft="true"
        android:layout_alignParentRight="true"
        android:textColor="#ffffff"
        android:textColorHint="#ffffff"
        android:hint="Final Snow Rate"
        android:singleLine="true" />

    <EditText
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:inputType="numberSigned"
        android:ems="10"
        android:id="@+id/windSpeed"
        android:layout_below="@+id/finalRate"
        android:layout_alignParentLeft="true"
        android:hint="Wind Speed"
        android:textColor="#ffffff"
        android:textColorHint="#ffffff"
        android:layout_alignParentRight="true"
        android:singleLine="true" />

    <EditText
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:inputType="numberDecimal"
        android:ems="10"
        android:id="@+id/snowGround"
        android:layout_below="@+id/windSpeed"
        android:layout_alignParentLeft="true"
        android:hint="Snow Already on Ground"
        android:textColor="#ffffff"
        android:textColorHint="#ffffff"
        android:layout_alignParentRight="true"
        android:singleLine="true" />

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Calculate"
        android:id="@+id/button"
        android:layout_below="@+id/snowGround"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="39dp" />

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textAppearance="?android:attr/textAppearanceLarge"
        android:id="@+id/resultView"
        android:layout_below="@+id/button"
        android:layout_alignRight="@+id/button"
        android:layout_marginTop="41dp"
        android:layout_alignLeft="@+id/button" />

</RelativeLayout>

主要 Activity :

package com.boreas.snowdaycalculatorsp2;

import java.util.Locale;

import android.support.v7.app.ActionBarActivity;
import android.support.v7.app.ActionBar;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentTransaction;
import android.support.v4.app.FragmentPagerAdapter;
import android.os.Bundle;
import android.support.v4.view.ViewPager;
import android.view.Gravity;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;

public class MainActivity extends ActionBarActivity implements ActionBar.TabListener {

    SectionsPagerAdapter mSectionsPagerAdapter;
    ViewPager mViewPager;

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

        // Set up the action bar.
        final ActionBar actionBar = getSupportActionBar();
        actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);

        // Create the adapter that will return a fragment for each of the three
        // primary sections of the activity.
        mSectionsPagerAdapter = new SectionsPagerAdapter(getSupportFragmentManager());

        // Set up the ViewPager with the sections adapter.
        mViewPager = (ViewPager) findViewById(R.id.pager);
        mViewPager.setAdapter(mSectionsPagerAdapter);

        // When swiping between different sections, select the corresponding
        // tab. We can also use ActionBar.Tab#select() to do this if we have
        // a reference to the Tab.
        mViewPager.setOnPageChangeListener(new ViewPager.SimpleOnPageChangeListener() {
            @Override
            public void onPageSelected(int position) {
                actionBar.setSelectedNavigationItem(position);
            }
        });

        // For each of the sections in the app, add a tab to the action bar.
        for (int i = 0; i < mSectionsPagerAdapter.getCount(); i++) {
            // Create a tab with text corresponding to the page title defined by
            // the adapter. Also specify this Activity object, which implements
            // the TabListener interface, as the callback (listener) for when
            // this tab is selected.
            actionBar.addTab(
                    actionBar.newTab()
                            .setText(mSectionsPagerAdapter.getPageTitle(i))
                            .setTabListener(this));
        }


    }


    @Override
    public boolean onCreateOptionsMenu(Menu menu) {

        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();
        if (id == R.id.action_settings) {
            return true;
        }
        return super.onOptionsItemSelected(item);
    }

    @Override
    public void onTabSelected(ActionBar.Tab tab, FragmentTransaction fragmentTransaction) {
        // When the given tab is selected, switch to the corresponding page in
        // the ViewPager.
        mViewPager.setCurrentItem(tab.getPosition());
    }

    @Override
    public void onTabUnselected(ActionBar.Tab tab, FragmentTransaction fragmentTransaction) {
    }

    @Override
    public void onTabReselected(ActionBar.Tab tab, FragmentTransaction fragmentTransaction) {
    }

    /**
     * A {@link FragmentPagerAdapter} that returns a fragment corresponding to
     * one of the sections/tabs/pages.
     */
    public class SectionsPagerAdapter extends FragmentPagerAdapter {

        public SectionsPagerAdapter(FragmentManager fm) {
            super(fm);
        }

        @Override
        public Fragment getItem(int position) {
            // getItem is called to instantiate the fragment for the given page.
            // Return a PlaceholderFragment (defined as a static inner class below).
            Fragment fragment;
            switch (position){
                case 0:
                    fragment = new BasicFragment();
                    break;
                case 1:
                    fragment = new AdvancedFragment();
                    break;
                default:
                    throw new IllegalArgumentException("Invalid Section Number");
            }




            return fragment;
        }

        @Override
        public int getCount() {
            // Show 3 total pages.
            return 2;
        }

        @Override
        public CharSequence getPageTitle(int position) {
            Locale l = Locale.getDefault();
            switch (position) {
                case 0:
                    return "Basic";
                case 1:
                    return "Advanced";

            }
            return null;
        }
    }
}

关于导致 NullPointerException 的原因有什么想法吗？

Answer 1

您应该使用 View 对象使用 inflater 来初始化 View

像这样

 @Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View view=inflater.inflate(R.layout.advfrag_layout, container, false);
    inSnow = (EditText) view.getView().findViewById(R.id.inchesSnow);
    durnStorm = (EditText)view.getView().findViewById(R.id.durationStorm);
    pSnow = (EditText)view. getView().findViewById(R.id.peakRate);
    pTime = (EditText)view.getView().findViewById(R.id.peakRateTime);
    fSnow = (EditText)view. getView().findViewById(R.id.finalRate);
    wSpeed = (EditText)view. getView().findViewById(R.id.windSpeed);
    sGround = (EditText) view.getView().findViewById(R.id.snowGround);
    results = (TextView)view. getView().findViewById(R.id.resultView);
    calc = (Button)view. getView().findViewById(R.id.button);

    return view;




}

或者你应该像这样在OnActivityCreated中初始化它

  @Override
public void onActivityCreated(Bundle savedInstanceState) {
// TODO Auto-generated method stub
super.onActivityCreated(savedInstanceState);
nSnow = (EditText) getView().findViewById(R.id.inchesSnow);
    durnStorm = (EditText)getView().findViewById(R.id.durationStorm);
    pSnow = (EditText) getView().findViewById(R.id.peakRate);
    pTime = (EditText)getView().findViewById(R.id.peakRateTime);
    fSnow = (EditText) getView().findViewById(R.id.finalRate);
    wSpeed = (EditText) getView().findViewById(R.id.windSpeed);
    sGround = (EditText) getView().findViewById(R.id.snowGround);
    results = (TextView) getView().findViewById(R.id.resultView);
    calc = (Button) getView().findViewById(R.id.button);

}

注意:您收到错误，因为 OnCreateView 试图在 Activity 的 OnCreate 完成之前执行。