android - java.lang.RuntimeException：无法启动活动 ComponentInfo{...EditCity}：java.lang.NullPointerException

Question

这是xml文件。

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent" >

<TextView
    android:id="@+id/textView1"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignParentLeft="true"
    android:layout_alignParentTop="true"
    android:layout_marginLeft="20dp"
    android:layout_marginTop="15dp"
    android:text="@string/edit_city"
    android:textAppearance="?android:attr/textAppearanceLarge" />

<TextView
    android:id="@+id/textView3"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignLeft="@+id/textView2"
    android:layout_below="@+id/cityName"
    android:layout_marginTop="20dp"
    android:text="@string/country_name" />

<EditText
    android:id="@+id/countryName"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignBottom="@+id/textView3"
    android:layout_alignLeft="@+id/cityName"
    android:ems="10"
    android:inputType="text" />

<TextView
    android:id="@+id/textView2"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_above="@+id/countryName"
    android:layout_alignLeft="@+id/textView1"
    android:text="@string/city_name" />

<EditText
    android:id="@+id/cityName"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_below="@+id/textView1"
    android:layout_toRightOf="@+id/textView1"
    android:ems="10"
    android:inputType="text" />

<TextView
    android:id="@+id/textView4"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignLeft="@+id/textView3"
    android:layout_below="@+id/textView3"
    android:layout_marginTop="20dp"
    android:text="@string/population" />

<EditText
    android:id="@+id/population"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignBottom="@+id/textView4"
    android:layout_alignLeft="@+id/countryName"
    android:ems="10"
    android:inputType="text" >

    <requestFocus />
</EditText>

<TextView
    android:id="@+id/textView5"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignLeft="@+id/textView4"
    android:layout_below="@+id/textView4"
    android:layout_marginTop="20dp"
    android:text="@string/traditions" />

<EditText
    android:id="@+id/traditions"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignBottom="@+id/textView5"
    android:layout_alignLeft="@+id/population"
    android:ems="10"
    android:inputType="text" />

<TextView
    android:id="@+id/textView6"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignLeft="@+id/textView5"
    android:layout_below="@+id/textView5"
    android:layout_marginTop="21dp"
    android:text="@string/impressions" />

<EditText
    android:id="@+id/impressions"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignBottom="@+id/textView6"
    android:layout_alignParentRight="true"
    android:ems="10"
    android:inputType="text" />

<TextView
    android:id="@+id/textView7"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignLeft="@+id/textView6"
    android:layout_below="@+id/textView6"
    android:layout_marginTop="21dp"
    android:text="@string/url_image" />

<EditText
    android:id="@+id/urlImage"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignBottom="@+id/textView7"
    android:layout_alignParentRight="true"
    android:ems="10"
    android:inputType="text" />

<Button
    android:id="@+id/button1"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignParentBottom="true"
    android:layout_marginBottom="38dp"
    android:layout_toRightOf="@+id/textView3"
    android:background="#444444"
    android:textColor="#FFFFFF"
    android:onClick="editCity"
    android:text="@string/edit_button" />

<Button
    android:id="@+id/button2"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignTop="@+id/button1"
    android:layout_marginLeft="56dp"
    android:layout_toRightOf="@+id/button1"
    android:background="#444444"
    android:onClick="displayCity"
    android:text="@string/view_button"
    android:textColor="#FFFFFF"
    android:textSize="20sp" />

  </RelativeLayout>

这是 logcat 内容。

09-10 16:55:15.975: D/AndroidRuntime(297): Shutting down VM
09-10 16:55:15.975: W/dalvikvm(297): threadid=1: thread exiting with uncaught exception (group=0x4001d800)
09-10 16:55:15.995: E/AndroidRuntime(297): FATAL EXCEPTION: main
09-10 16:55:15.995: E/AndroidRuntime(297): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.citiestoremember/com.example.citiestoremember.EditCity}: java.lang.NullPointerException
09-10 16:55:15.995: E/AndroidRuntime(297):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2663)
09-10 16:55:15.995: E/AndroidRuntime(297):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2679)
09-10 16:55:15.995: E/AndroidRuntime(297):  at android.app.ActivityThread.access$2300(ActivityThread.java:125)
09-10 16:55:15.995: E/AndroidRuntime(297):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2033)
09-10 16:55:15.995: E/AndroidRuntime(297):  at android.os.Handler.dispatchMessage(Handler.java:99)
09-10 16:55:15.995: E/AndroidRuntime(297):  at android.os.Looper.loop(Looper.java:123)
09-10 16:55:15.995: E/AndroidRuntime(297):  at android.app.ActivityThread.main(ActivityThread.java:4627)
09-10 16:55:15.995: E/AndroidRuntime(297):  at java.lang.reflect.Method.invokeNative(Native Method)
09-10 16:55:15.995: E/AndroidRuntime(297):  at java.lang.reflect.Method.invoke(Method.java:521)
09-10 16:55:15.995: E/AndroidRuntime(297):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
09-10 16:55:15.995: E/AndroidRuntime(297):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
09-10 16:55:15.995: E/AndroidRuntime(297):  at dalvik.system.NativeStart.main(Native Method)
09-10 16:55:15.995: E/AndroidRuntime(297): Caused by: java.lang.NullPointerException
09-10 16:55:15.995: E/AndroidRuntime(297):  at com.example.citiestoremember.EditCity.onCreate(EditCity.java:44)
09-10 16:55:15.995: E/AndroidRuntime(297):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
09-10 16:55:15.995: E/AndroidRuntime(297):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2627)
09-10 16:55:15.995: E/AndroidRuntime(297):  ... 11 more

你好！当我运行我的程序时，它一直运行良好，直到某个特定时刻。我在我的 logcat 中收到此错误。

发生错误的 EditCity.java 文件如下。谁能帮我？谢谢！

package com.example.citiestoremember;

import java.util.HashMap;

import android.app.Activity;
import android.app.ListActivity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.EditText;

public class EditCity extends Activity{

EditText cityName;
EditText countryName;
EditText populationNumber;
EditText traditions;
EditText impressions;
EditText urlImage;

DBTools dbTools = new DBTools(this);

public void onCreate(Bundle savedInstanceState){

    super.onCreate(savedInstanceState);
    setContentView(R.layout.edit_city);
    cityName = (EditText) findViewById(R.id.cityName);
    countryName = (EditText) findViewById(R.id.countryName);
    populationNumber = (EditText) findViewById(R.id.populationNumber);
    traditions = (EditText) findViewById(R.id.traditions);
    impressions = (EditText) findViewById(R.id.impressions);
    urlImage = (EditText) findViewById(R.id.urlImage);

    Intent theIntent = getIntent();

    String cityId = theIntent.getStringExtra("cityId");

    HashMap<String, String> cityList = dbTools.getCityInfo(cityId);

    if(cityList.size() != 0){

        cityName.setText(cityList.get("cityName"));
        countryName.setText(cityList.get("countryName"));
        populationNumber.setText(cityList.get("populationNumber"));
        traditions.setText(cityList.get("traditions"));
        impressions.setText(cityList.get("impressions"));
        urlImage.setText(cityList.get("urlImage"));

    }
}

public void editCity(View view){

    HashMap<String, String> queryValuesMap = new HashMap<String, String>();

    cityName = (EditText) findViewById(R.id.cityName);
    countryName = (EditText) findViewById(R.id.countryName);
    populationNumber = (EditText) findViewById(R.id.populationNumber);
    traditions = (EditText) findViewById(R.id.traditions);
    impressions = (EditText) findViewById(R.id.impressions);
    urlImage = (EditText) findViewById(R.id.urlImage);

    Intent theIntent = getIntent();

    String cityId = theIntent.getStringExtra("cityId");

    queryValuesMap.put("cityId", cityId);
    queryValuesMap.put("cityName", cityName.getText().toString());
    queryValuesMap.put("countryName", countryName.getText().toString());
    queryValuesMap.put("populationNumber", populationNumber.getText().toString());
    queryValuesMap.put("traditions", traditions.getText().toString());
    queryValuesMap.put("impressions", impressions.getText().toString());
    queryValuesMap.put("urlImage", urlImage.getText().toString());

    dbTools.updateCity(queryValuesMap);
    this.callMainActivity(view);

}

public void displayCity(View view){

    Intent theIntent = new Intent(getApplicationContext(), DisplayImage.class);
    String urlImage = theIntent.getStringExtra("urlImage");
    theIntent.putExtra("urlImage", urlImage); 

    startActivity(theIntent);

}

public void callMainActivity(View view){

    Intent objIntent = new Intent(getApplication(), MainActivity.class);

    startActivity(objIntent);

}

 }

score 0 · Accepted Answer

尝试这个：-

DBTools dbTools ;

public void onCreate(Bundle savedInstanceState){

    super.onCreate(savedInstanceState);
    setContentView(R.layout.edit_city);
    dbTools = new DBTools(this);
    cityName = (EditText) findViewById(R.id.cityName);
    countryName = (EditText) findViewById(R.id.countryName);
    populationNumber = (EditText) findViewById(R.id.populationNumber);
    traditions = (EditText) findViewById(R.id.traditions);
    impressions = (EditText) findViewById(R.id.impressions);
    urlImage = (EditText) findViewById(R.id.urlImage);

    Intent theIntent = getIntent();

    String cityId = theIntent.getStringExtra("cityId");

    HashMap<String, String> cityList = dbTools.getCityInfo(cityId);

    if(cityList.size() != 0){

        cityName.setText(cityList.get("cityName"));
        countryName.setText(cityList.get("countryName"));
        populationNumber.setText(cityList.get("populationNumber"));
        traditions.setText(cityList.get("traditions"));
        impressions.setText(cityList.get("impressions"));
        urlImage.setText(cityList.get("urlImage"));

    }
}

您不会this在活动开始或运行之前启动价值。第一个活动开始，然后您必须获取活动的上下文或您的应用程序（this，getBasecontext()等）。

在上面您在活动开始之前启动此操作，这就是 logcat 说空指针异常的原因。

android - java.lang.RuntimeException：无法启动活动 ComponentInfo{...EditCity}：java.lang.NullPointerException

1 回答 1

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