Java Android应用程序打开后立即关闭

在设备上安装应用程序后，应用程序在打开后立即关闭

我正在通过Udacity学习android。在第三课中，他们给了我一个带有 最小布局。[Udacity代码][1]。因此，他们要求开发以适配器视图格式显示震级位置和日期的完整代码

Studio没有显示任何错误，但如果我将光标放在getMagnitude（）方法上，它会显示方法调用getMagnitude可能会产生“java.lang.NullPointerException”，而对于setAdapter，它也显示相同的内容，我的完整代码如下所示

EarthquakeActivity.java




/*``
 * Copyright (C) 2016 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.example.android.quakereport;
import java.lang.String;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.widget.ArrayAdapter;
import android.widget.ListView;

import java.util.ArrayList;

public class EarthquakeActivity extends AppCompatActivity {

    public static final String LOG_TAG = EarthquakeActivity.class.getName();

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

        // Create a fake list of earthquake locations.
        ArrayList<Earthquake> earthquakes = new ArrayList<>();
        earthquakes.add(new Earthquake("7.2","San Francisco", "Feb 2,2017 "));
        earthquakes.add(new Earthquake("5.2","London", "Oct 2,2017 "));
        earthquakes.add(new Earthquake("9.2","Tokyo", "Feb 2,2017 "));
        earthquakes.add(new Earthquake("8.2","Mexico City", "Mar 2,2017 "));
        earthquakes.add(new Earthquake("7.2","Mascow", "Feb 16,2017 "));
        earthquakes.add(new Earthquake("6.2","Rio de Jeneiro", "Feb 28,2017 "));
        earthquakes.add(new Earthquake("1.2","India", "Jan 2,2017 "));


        // Find a reference to the {@link ListView} in the layout
        ListView earthquakeListView = (ListView) findViewById(R.id.list);

        // Create a new {@link ArrayAdapter} of earthquakes
  EarthquakeAdapter adapter = new EarthquakeAdapter(this ,earthquakes);

        // Set the adapter on the {@link ListView}
        // so the list can be populated in the user interface
        earthquakeListView.setAdapter(adapter);
    }
}

EarthquakeAdapter.java

package com.example.android.quakereport;

import android.content.Context;
import android.support.annotation.NonNull;
import android.support.v7.view.menu.ListMenuItemView;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.LinearLayout;
import android.widget.TextView;

import java.util.List;

/**
 * Created by raghavendra on 3/7/2017.
 */

public class EarthquakeAdapter extends ArrayAdapter<Earthquake> {

    public EarthquakeAdapter(Context context, List<Earthquake> earthquakes) {
        super(context, 0, earthquakes);
    }


    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        // Check if the existing view is being reused, otherwise inflate the view
        View listItemView = convertView;
        if (listItemView == null) {
            listItemView = LayoutInflater.from(getContext()).inflate(
                    R.layout.earthquake_activity, parent, false);
        }

        Earthquake currentEarthquake = getItem(position);



        TextView magnitudeView  = (TextView) listItemView.findViewById(R.id.magnitude);

        magnitudeView.setText(currentEarthquake.getMagnitude());

        TextView locationView  = (TextView) listItemView.findViewById(R.id.location);

        locationView.setText(currentEarthquake.getLocation());

        TextView dateView  = (TextView) listItemView.findViewById(R.id.date);

       dateView.setText(currentEarthquake.getDate());






return listItemView;



    }

}








  [1]: https://github.com/udacity/ud843-QuakeReport

package com.example.android.quakereport；
导入android.content.Context；
导入android.support.annotation.NonNull；
导入android.support.v7.view.menu.ListMenuItemView；
导入android.view.LayoutInflater；
导入android.view.view；
导入android.view.ViewGroup；
导入android.widget.ArrayAdapter；
导入android.widget.LinearLayout；
导入android.widget.TextView；
导入java.util.List；
/**
*由raghavendra于2017年3月7日创建。
*/
公共类地震适配器扩展阵列适配器{
公共地震适配器（上下文，列出地震）{
超级（上下文，0，地震）；
}
@凌驾
公共视图getView（int位置、视图转换视图、视图组父视图）{
//检查现有视图是否正在重新使用，否则会膨胀视图
View listItemView=convertView；
如果（listItemView==null）{
listItemView=LayoutFlater.from（getContext（））.inflate(
R.layou.u活动，父项，假）；
}
地震电流地震=getItem（位置）；
TextView magnitudeView=（TextView）listItemView.findViewById（R.id.magnitude）；
震级视图.setText（current地震.getMagnite（））；
TextView locationView=（TextView）listItemView.findViewById（R.id.location）；
locationView.setText（currentSe震.getLocation（））；
TextView dateView=（TextView）listItemView.findViewById（R.id.date）；
dateView.setText（currentSevent.getDate（））；
返回listItemView；
}
}
[1]: https://github.com/udacity/ud843-QuakeReport

地震类没有默认构造函数。因此，mMagnitude可以为null，您应该将其设置为

private String mMagnitude = "";

或者为地震类添加默认构造函数：

public Earthquake() {
    mMagnitude = "";
    ...
}

---

我认为问题在于你的地震.java

package com.example.android.quakereport;

/**
 * Created by raghavendra on 3/7/2017.
 */

public class Earthquake {


    private  String mMagnitude;

    private String mLocation;

    private String mDate;


    public Earthquake(String Magnitude, String Location, String Date)
    {
        mMagnitude = Magnitude;

        mLocation = Location;

        mDate = Date;

    }

    public String getMagnitude()
    {

        return mMagnitude;
    }

    public String getLocation()
    {

        return mLocation;
    }

    public String getDate()
    {

        return mDate;
    }




}

尝试

---

请大家找出问题所在。请发布错误日志。您上传的代码中没有GetMagnite。这只是本课程的起点。请推送您的更改。您的变量名称应为大写。公共地震（弦震级、弦位置、弦日期）{mMagnitude=震级；mLocation=位置；mDate=日期；}@GustavoConde camelCase是个人喜好的问题。它不会以任何方式影响应用程序的性能。

public class Earthquake {


    private  String mMagnitude;

    private String mLocation;

    private String mDate;


    public Earthquake(String Magnitude, String Location, String Date)
    {
        this.mMagnitude = Magnitude;

        this.mLocation = Location;

        this.mDate = Date;

    }

    public String getMagnitude()
    {

        return mMagnitude;
    }

    public String getLocation()
    {

        return mLocation;
    }

    public String getDate()
    {

        return mDate;
    }
}