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Android的錯誤顯示java.lang.NullPointerException：嘗試調用虛擬方法無效android.widget.ListView.setOnItemClickListener

2017-01-06 47 views
-2

我想建立一個簡單的列表視圖的應用程序，但我不斷收到這個惱人的錯誤。我是相當新到Android，所以我真的不知道如何解決它。任何幫助表示讚賞。Android的錯誤顯示java.lang.NullPointerException：嘗試調用虛擬方法無效android.widget.ListView.setOnItemClickListener

錯誤行是在這裏BirthdayReminderActivity.java：

listView.setOnItemClickListener（新OnItemClickListener（）{

logcat的錯誤輸出是：

--------- beginning of crash 
    E/AndroidRuntime: FATAL EXCEPTION: main 
       Process: premprakash.birthdayreminder, PID: 2266 
       java.lang.RuntimeException: Unable to start activity ComponentInfo{premprakash.birthdayreminder/premprakash.birthdayreminder.BirthdayReminderActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ListView.setOnItemClickListener(android.widget.AdapterView$OnItemClickListener)' on a null object reference 
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2646) 
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2707) 
        at android.app.ActivityThread.-wrap12(ActivityThread.java) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1460) 
        at android.os.Handler.dispatchMessage(Handler.java:102) 
        at android.os.Looper.loop(Looper.java:154) 
        at android.app.ActivityThread.main(ActivityThread.java:6077) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:865) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:755) 
       Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ListView.setOnItemClickListener(android.widget.AdapterView$OnItemClickListener)' on a null object reference 
        at premprakash.birthdayreminder.BirthdayReminderActivity.onCreate(BirthdayReminderActivity.java:51) 
        at android.app.Activity.performCreate(Activity.java:6662) 
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1118) 
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2599) 
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2707)  
        at android.app.ActivityThread.-wrap12(ActivityThread.java)  
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1460)  
        at android.os.Handler.dispatchMessage(Handler.java:102)  
        at android.os.Looper.loop(Looper.java:154)  
        at android.app.ActivityThread.main(ActivityThread.java:6077)  
        at java.lang.reflect.Method.invoke(Native Method)  
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:865)  
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:755)  

Application terminated.

BirthdayReminderActivity。 java的

package premprakash.birthdayreminder; 

import android.content.Intent; 

import android.support.v7.app.AppCompatActivity; 

import android.os.Bundle; 

import android.view.Gravity; 

import android.view.View; 

import android.widget.Button; 

import android.widget.Toast; 

import android.widget.AdapterView; 

import android.os.Handler; 

import android.util.Log; 

import android.widget.AdapterView.OnItemClickListener; 

import android.widget.ListView; 


public class BirthdayReminderActivity extends AppCompatActivity { 

private CustomCursorAdapterBirthday customAdapter; 
private BirthdayDatabaseHelper databaseHelper; 
private static final int ENTER_BIRTHDAY_REQUEST_CODE = 1; 
private ListView listView; 

private static final String TAG = BirthdayReminderActivity.class.getSimpleName(); 

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

    Button add = (Button) findViewById(R.id.add); 


    databaseHelper = new BirthdayDatabaseHelper(this); 

    listView = (ListView) findViewById(R.id.list_birthday); 


    listView.setOnItemClickListener(new OnItemClickListener() { 

     @Override 
     public void onItemClick(AdapterView<?> parent, View view, int position, long id) { 
      Log.d(TAG, "clicked on item: " + position); 
     } 
    }); 

    // Database query can be a time consuming task .. 
    // so its safe to call database query in another thread 
    // Handler, will handle this stuff for you <img src="http://s0.wp.com/wp-includes/images/smilies/icon_smile.gif?m=1129645325g" alt=":)" class="wp-smiley"> 

    new Handler().post(new Runnable() { 
     @Override 
     public void run() { 
      customAdapter = new CustomCursorAdapterBirthday(BirthdayReminderActivity.this, databaseHelper.getAllBirthday()); 

      System.out.println("dsafjkdsjflkdsjfkdsjf"); 
      listView.setAdapter(customAdapter); 
     } 
    }); 

} 

public void onClickAdd(View add) { 

    add.setOnClickListener(new View.OnClickListener() { 
     @Override 
     public void onClick(View v) { 
      Toast toast = Toast.makeText(getApplicationContext(), "Successfully Added", Toast.LENGTH_SHORT); 
      toast.setGravity(Gravity.BOTTOM, 0, 0); 
      toast.show(); 
      startActivity(new Intent(BirthdayReminderActivity.this, ReminderTypesActivity.class)); 
     } 
    }); 
} 


@Override 
protected void onActivityResult(int requestCode, int resultCode, Intent birthday) { 

    super.onActivityResult(requestCode, resultCode, birthday); 

    if (requestCode == ENTER_BIRTHDAY_REQUEST_CODE && resultCode == RESULT_OK) { 

     databaseHelper.insertBirthday(birthday.getExtras().getString("tag_name"), birthday.getExtras().getString("tag_date"), birthday.getExtras().getString("tag_setalarm"), birthday.getExtras().getString("tag_date1"), birthday.getExtras().getString("tag_time")); 

     customAdapter.changeCursor(databaseHelper.getAllBirthday()); 
     } 
    } 
    }

birthdayreminderactivity.xml

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

<RelativeLayout 
xmlns:android="http://schemas.android.com/apk/res/android" 
xmlns:tools="http://schemas.android.com/tools" 
android:id="@+id/activity_birthday_reminder" 
android:layout_width="match_parent" 
android:layout_height="match_parent" 
android:paddingLeft="@dimen/activity_horizontal_margin" 
android:paddingRight="@dimen/activity_horizontal_margin" 
android:paddingTop="@dimen/activity_vertical_margin" 
android:paddingBottom="@dimen/activity_vertical_margin" 
tools:context="premprakash.birthdayreminder.BirthdayReminderActivity"> 

<Button 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:layout_alignParentBottom="true" 
    android:layout_alignParentLeft="true" 
    android:layout_alignParentStart="true" 
    android:id="@+id/add" 
    android:visibility="visible" 
    android:contextClickable="true" 
    tools:text="@string/add" 
    android:onClick="onClickAdd" 
    tools:ignore="UnusedAttribute" /> 

<SearchView 
    android:layout_width="match_parent" 
    android:layout_height="match_parent" 
    android:layout_alignParentBottom="true" 
    android:layout_toRightOf="@+id/add" 
    android:layout_alignTop="@+id/add" 
    android:id="@+id/search" 
    android:orientation="vertical" 
    android:filterTouchesWhenObscured="false" 
    android:focusableInTouchMode="true" 
    tools:focusableInTouchMode="false" 
    android:clickable="true" 
    tools:ignore="RtlHardcoded" /> 

<ListView 
    android:layout_width="match_parent" 
    android:layout_height="match_parent" 
    tools:ignore="NestedScrolling" 
    android:id="@+id/list_birthday" 
    android:layout_alignParentTop="true" 
    android:layout_alignParentLeft="true" 
    android:layout_alignParentStart="true" /> 

</RelativeLayout>

的manifest.xml

<?xml version="1.0" encoding="utf-8"?> 
<manifest xmlns:android="http://schemas.android.com/apk/res/android" 
package="premprakash.birthdayreminder"> 

<application 
    android:allowBackup="true" 
    android:icon="@mipmap/ic_launcher" 
    android:label="@string/app_name" 
    android:supportsRtl="true" 
    android:theme="@style/AppTheme"> 
    <activity android:name=".BirthdayReminderActivity"> 
     <intent-filter> 
      <action android:name="android.intent.action.BIRTHDAYREMINDER" /> 

      <category android:name="android.intent.category.LAUNCHER" /> 
     </intent-filter> 
    </activity> 

    <activity android:name=".ReminderTypesActivity"> 
     <intent-filter> 
      <action android:name="android.intent.action.REMINDERTYPES" /> 

      <category android:name="android.intent.category.LAUNCHER" /> 
     </intent-filter> 
    </activity> 

    <activity android:name=".BirthdayFormActivity"> 
     <intent-filter> 
      <action android:name="android.intent.action.BIRTHDAYFORM" /> 

      <category android:name="android.intent.category.LAUNCHER" /> 
     </intent-filter> 
    </activity> 

    <activity android:name=".AnniversaryFormActivity"> 
     <intent-filter> 
      <action android:name="android.intent.action.ANNIVERSARYFORM" /> 

      <category android:name="android.intent.category.LAUNCHER" /> 
     </intent-filter> 
    </activity> 

    <activity android:name=".OthersFormActivity"> 
     <intent-filter> 
      <action android:name="android.intent.action.OTHERSFORM" /> 

      <category android:name="android.intent.category.LAUNCHER" /> 
     </intent-filter> 
    </activity> 

</application>

CustomCursorAdapterBirthday.java

package premprakash.birthdayreminder; 

import android.content.Context; 
import android.database.Cursor; 
import android.view.LayoutInflater; 
import android.view.View; 
import android.view.ViewGroup; 
import android.widget.CursorAdapter; 
import android.widget.TextView; 


public class CustomCursorAdapterBirthday extends CursorAdapter { 

public CustomCursorAdapterBirthday(Context context, Cursor c) { 
    super(context, c); 
} 

@Override 
public View newView(Context context, Cursor cursor, ViewGroup parent) { 
    // when the view will be created for first time, 
    // we need to tell the adapters, how each item will look 
    LayoutInflater inflater = LayoutInflater.from(parent.getContext()); 
    View retView = inflater.inflate(R.layout.activity_birthday_reminder, parent, false); 

    return retView; 
    } 

@Override 
public void bindView(View view, Context context, Cursor cursor) { 
    // here we are setting our data 
    // that means, take the data from the cursor and put it in views 

    TextView textViewName = (TextView) view.findViewById(R.id.name); 
    textViewName.setText(cursor.getString(cursor.getColumnIndex(cursor.getColumnName(1)))); 

    TextView textViewDate = (TextView) view.findViewById(R.id.date); 
    textViewDate.setText(cursor.getString(cursor.getColumnIndex(cursor.getColumnName(2)))); 

    TextView textViewSetalarm = (TextView) view.findViewById(R.id.setalarm); 
    textViewSetalarm.setText(cursor.getString(cursor.getColumnIndex(cursor.getColumnName(3)))); 

    TextView textViewDate1 = (TextView) view.findViewById(R.id.date); 
    textViewDate1.setText(cursor.getString(cursor.getColumnIndex(cursor.getColumnName(4)))); 

    TextView textViewTime = (TextView) view.findViewById(R.id.time); 
    textViewTime.setText(cursor.getString(cursor.getColumnIndex(cursor.getColumnName(5)))); 

    } 
}

BirthdayDatabaseHelper.java

package premprakash.birthdayreminder; 


import android.content.ContentValues; 
import android.content.Context; 
import android.database.Cursor; 
import android.database.sqlite.SQLiteDatabase; 
import android.database.sqlite.SQLiteOpenHelper; 
import android.util.Log; 

public class BirthdayDatabaseHelper { 

private static final String TAG = BirthdayDatabaseHelper.class.getSimpleName(); 

// database configuration 
// if you want the onUpgrade to run then change the database_version 
private static final int DATABASE_VERSION = 4; 
private static final String DATABASE_NAME = "birthdaydatabase.db"; 

// table configuration 
private static final String TABLE_NAME = "birthday";   // Table name 
private static final String BIRTHDAY_TABLE_COLUMN_ID = "_id";  // a column named "_id" is required for cursor 
private static final String BIRTHDAY_TABLE_COLUMN_NAME = "name"; 
private static final String BIRTHDAY_TABLE_COLUMN_DATE = "date"; 
private static final String BIRTHDAY_TABLE_COLUMN_SETALARM = "setalarm"; 
private static final String BIRTHDAY_TABLE_COLUMN_DATE1 = "date1"; 
private static final String BIRTHDAY_TABLE_COLUMN_TIME = "time"; 

private DatabaseOpenHelper openHelper; 
private SQLiteDatabase database; 

// this is a wrapper class. that means, from outside world, anyone will communicate with PersonDatabaseHelper, 
// but under the hood actually DatabaseOpenHelper class will perform database CRUD operations 
public BirthdayDatabaseHelper(Context Context) { 

    openHelper = new DatabaseOpenHelper(Context); 
    database = openHelper.getWritableDatabase(); 
} 

public void insertBirthday (String Name, String Date, String Setalarm, String Date1, String Time) { 

    // we are using ContentValues to avoid sql format errors 

    ContentValues contentValues = new ContentValues(); 

    contentValues.put(BIRTHDAY_TABLE_COLUMN_NAME, Name); 
    contentValues.put(BIRTHDAY_TABLE_COLUMN_DATE, Date); 
    contentValues.put(BIRTHDAY_TABLE_COLUMN_SETALARM, Setalarm); 
    contentValues.put(BIRTHDAY_TABLE_COLUMN_DATE1, Date1); 
    contentValues.put(BIRTHDAY_TABLE_COLUMN_TIME, Time); 

    database.insert(TABLE_NAME, null, contentValues); 
    } 

    public Cursor getAllBirthday() { 

    String buildSQL = "SELECT * FROM " + TABLE_NAME; 

    Log.d(TAG, "getAllBirthday SQL: " + buildSQL); 

    System.out.println("HKJHDSFKJDhf"); 

    return database.rawQuery(buildSQL, null); 
    } 

// this DatabaseOpenHelper class will actually be used to perform database related operation 

private class DatabaseOpenHelper extends SQLiteOpenHelper { 

    public DatabaseOpenHelper(Context Context) { 
     super(Context, DATABASE_NAME, null, DATABASE_VERSION); 
    } 

    @Override 
    public void onCreate(SQLiteDatabase sqLiteDatabase) { 
     // Create your tables here 

     String buildSQL = "CREATE TABLE " + TABLE_NAME + "(" + BIRTHDAY_TABLE_COLUMN_ID + " INTEGER PRIMARY KEY, " + BIRTHDAY_TABLE_COLUMN_NAME + " TEXT, " + BIRTHDAY_TABLE_COLUMN_DATE + " TEXT, " + BIRTHDAY_TABLE_COLUMN_SETALARM + " TEXT, " + BIRTHDAY_TABLE_COLUMN_DATE1 + " TEXT, " + BIRTHDAY_TABLE_COLUMN_TIME + " TEXT)"; 

     Log.d(TAG, "onCreate SQL: " + buildSQL); 

     sqLiteDatabase.execSQL(buildSQL); 
    } 

    @Override 
    public void onUpgrade(SQLiteDatabase sqLiteDatabase, int oldVersion, int newVersion) { 
     // Database schema upgrade code goes here 

     String buildSQL = "DROP TABLE IF EXISTS " + TABLE_NAME; 

     Log.d(TAG, "onUpgrade SQL: " + buildSQL); 

     sqLiteDatabase.execSQL(buildSQL);  // drop previous table 

     onCreate(sqLiteDatabase);    // create the table from the beginning 
     } 
    } 
    }

來源

2017-01-06 Premprakash

+3

** R.layout.activity_birthday_reminder = birthdayreminderactivity.xml ** –

回答

0

這是一個標準的空指針異常即您試圖訪問的對象不存在。在你的情況，你的活動一直沒能找到你的ListView，所以findViewById返回一個空對象。

我懷疑這條線是在BirthdayReminderActivity.java問題：

setContentView(R.layout.activity_birthday_reminder);

這是一個不同的名稱，你所提供的xml文件（birthdayreminderactivity.xml），所以你的活動改爲充氣名爲activity_birthday_reminder文件。嘗試將其更改爲：

setContentView(R.layout.birthdayreminderactivity);

來源

2017-01-06 15:43:12

0

您與LinearLayout中，而不是佈局文件名的ID設置你的內容查看

setContentView(R.layout.birthdayreminderactivity);

來源

2017-01-06 15:44:18

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