为什么我在这段代码中得到一个NullPointerException

-6

07-14 16:13:53.385 19921-19921/studentzone.studentzone E/AndroidRuntime: FATAL EXCEPTION: main 
Process: studentzone.studentzone, PID: 19921 
java.lang.IllegalStateException: Could not execute method for android:onClick 
    at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:293) 
    at android.view.View.performClick(View.java:4444) 
    at android.view.View$PerformClick.run(View.java:18457) 
    at android.os.Handler.handleCallback(Handler.java:733) 
    at android.os.Handler.dispatchMessage(Handler.java:95) 
    at android.os.Looper.loop(Looper.java:136) 
    at android.app.ActivityThread.main(ActivityThread.java:5113) 
    at java.lang.reflect.Method.invokeNative(Native Method) 
    at java.lang.reflect.Method.invoke(Method.java:515) 
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793) 
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:609) 
    at dalvik.system.NativeStart.main(Native Method) 
Caused by: java.lang.reflect.InvocationTargetException 
    at java.lang.reflect.Method.invokeNative(Native Method) 
    at java.lang.reflect.Method.invoke(Method.java:515) 
    at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:288) 
    at android.view.View.performClick(View.java:4444) 
    at android.view.View$PerformClick.run(View.java:18457) 
    at android.os.Handler.handleCallback(Handler.java:733) 
    at android.os.Handler.dispatchMessage(Handler.java:95) 
    at android.os.Looper.loop(Looper.java:136) 
    at android.app.ActivityThread.main(ActivityThread.java:5113) 
    at java.lang.reflect.Method.invokeNative(Native Method) 
    at java.lang.reflect.Method.invoke(Method.java:515) 
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793) 
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:609) 
    at dalvik.system.NativeStart.main(Native Method) 
Caused by: android.database.sqlite.SQLiteException: near "tableuser": syntax error (code 1): , while compiling: create tableuser(abctextemailemailtextemail12345text) 
    at android.database.sqlite.SQLiteConnection.nativePrepareStatement(Native Method) 
    at android.database.sqlite.SQLiteConnection.acquirePreparedStatement(SQLiteConnection.java:889) 
    at android.database.sqlite.SQLiteConnection.prepare(SQLiteConnection.java:500) 
    at android.database.sqlite.SQLiteSession.prepare(SQLiteSession.java:588) 
    at android.database.sqlite.SQLiteProgram.<init>(SQLiteProgram.java:58) 
    at android.database.sqlite.SQLiteStatement.<init>(SQLiteStatement.java:31) 
    at android.database.sqlite.SQLiteDatabase.executeSql(SQLiteDatabase.java:1672) 
    at android.database.sqlite.SQLiteDatabase.execSQL(SQLiteDatabase.java:1603) 
    at studentzone.studentzone.DataBaseHelper.onCreate(DataBaseHelper.java:30) 
    at android.database.sqlite.SQLiteOpenHelper.getDatabaseLocked(SQLiteOpenHelper.java:252) 
    at android.database.sqlite.SQLiteOpenHelper.getWritableDatabase(SQLiteOpenHelper.java:164) 
    at studentzone.studentzone.DataBaseHelper.insertData(DataBaseHelper.java:43) 
    at studentzone.studentzone.SignUp.register(SignUp.java:31) 
    at java.lang.reflect.Method.invokeNative(Native Method) 
    at java.lang.reflect.Method.invoke(Method.java:515) 
    at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:288) 
    at android.view.View.performClick(View.java:4444) 
    at android.view.View$PerformClick.run(View.java:18457) 
    at android.os.Handler.handleCallback(Handler.java:733) 
    at android.os.Handler.dispatchMessage(Handler.java:95) 
    at android.os.Looper.loop(Looper.java:136) 
    at android.app.ActivityThread.main(ActivityThread.java:5113) 
    at java.lang.reflect.Method.invokeNative(Native Method) 
    at java.lang.reflect.Method.invoke(Method.java:515) 
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793) 
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:609) 
    at dalvik.system.NativeStart.main(Native Method)

我的数据库类是：

public class DataBaseHelper extends SQLiteOpenHelper { 

    public static final String Database_name="studentzone.db"; 
    public static final String Table_name ="user"; 
    public static final String Type ="text"; 
    public static final String comma ="email"; 
    public static final String Name ="abc"; 
    public static final String Email ="email"; 
    public static final String Pass ="12345"; 
    public static final String sql_create="create table"+Table_name+"("+Name+Type+comma+Email+Type+comma+Pass+Type+")"; 
    public static final String sql_delete="drop table if exists" + DataBaseHelper.Table_name; 

    public DataBaseHelper(Context context) { 
     super(context,Database_name, null, 1); 
    } 

    @Override 
    public void onCreate(SQLiteDatabase db) { 
     db.execSQL(sql_create); 


    } 

    @Override 
    public void onUpgrade(SQLiteDatabase db, int i, int i1) { 
     db.execSQL(sql_delete); 
     onCreate(db); 
    } 

    public Boolean insertData(String name , String email , String password) 
    { 
     SQLiteDatabase db = this.getWritableDatabase(); 
     ContentValues contentValues = new ContentValues(); 
     contentValues.put(Name,name); 
     contentValues.put(Email,email); 
     contentValues.put(Pass,password); 
     long rslt =db.insert(Table_name,null,contentValues); 
     if(rslt==-1) 
     { 
      return false; 

     } 
      else 
     { 
      return true; 
     } 

    } 
}

我的主类是：

public class SignUp extends AppCompatActivity { 

DataBaseHelper Database; 

    Button login; 

    EditText editName, editEmail,editPassword; 

    @Override 

    protected void onCreate(Bundle savedInstanceState) { 

     super.onCreate(savedInstanceState); 

     setContentView(R.layout.activity_sign_up); 

     login= (Button) findViewById(R.id.button_login); 

     editName= (EditText) findViewById(R.id.edit_text_full_name); 

     editEmail= (EditText) findViewById(R.id.edit_text_email); 

     editPassword= (EditText) findViewById(R.id.edit_text_password); 

     Database=new DataBaseHelper(this); 

    } 
    public void register(View v) 
    { 
     Toast.makeText(SignUp.this,editName.getText().toString(), Toast.LENGTH_SHORT).show(); 
     Toast.makeText(SignUp.this,editEmail.getText().toString(), Toast.LENGTH_SHORT).show(); 
     Toast.makeText(SignUp.this,editPassword.getText().toString(), Toast.LENGTH_SHORT).show(); 
     boolean isInserted=Database.insertData(editName.getText().toString(),editEmail.getText().toString(),editPassword.getText().toString()); 
     if(isInserted==true) 
     { 

      Toast.makeText(getApplicationContext(),"value inserted",Toast.LENGTH_SHORT).show(); 
     } 
     else 
     { 

      Toast.makeText(getApplicationContext(),"no value inserted",Toast.LENGTH_SHORT).show(); 
     } 

    } 

    public void login(View v) 

    { 
     Intent intent = new Intent(SignUp.this,LoginActivity.class); 
     startActivity(intent); 


    } 
}

来源

2016-07-14 Tarun

您的堆栈跟踪任何地方都不会显示一个NullPointerException。它显示了一个SQLiteException。 –

有你的代码中有几个问题。他们中很少有人如下：

public static final String sql_create="create table"+Table_name+"("+Name+Type+comma+Email+Type+comma+Pass+Type+")";

你缺少常量字符串和变量之间的空间： 表“+ table_name的应该表” + table_name的

而且，同样的问题是在这条线在你的数据库类：

public static final String sql_delete="drop table if exists" + DataBaseHelper.Table_name;

应该是存在“+ TABLE_NAME

public static final String comma =“email”;还有另一个问题。应该是真的逗号，所以String comma =“，”;

public static final String Table_name ="user"; 
public static final String Type ="text"; 
public static final String comma ="email"; 
public static final String Name ="abc"; 
public static final String Email ="email"; 
public static final String Pass ="12345";

这对create语句是错误的，因为这显然包含值而不是CREATE TABLE语句的列名。我认为你的意图是在这些变量中有列名。所以它应该看起来像：

public static final String Table_name ="user"; 
public static final String Type ="type"; 
public static final String comma =","; 
public static final String Name ="name"; 
public static final String Email ="email"; 
public static final String Pass ="password";

而最后一件事是，CREATE TABLE语句缺少数据类型。 See CREATE TABLE statement here

来源

2016-07-14 11:00:07 holmicz

'由于：android.database.sqlite.SQLiteException：near“tableuser”：语法错误（代码1）：，编译时：create tableuser（abctextemailemailtextemail12345text）'...并且也适用于列定义。 – Fildor

我不认为你已经做出了正确的改变。你能在这里粘贴更改吗？公共静态最终字符串comma =“email”还有另一个问题;应该是真的逗号，所以String comma =“，”; – holmicz

ErrorReport：发送HttpRequestorg.json.JSONException失败：值java.lang.String类型的<！DOCTYPE无法在org.json.JSON.typeMismatch（JSON.java:111）上的org.json.JSONObject上转换为JSONObject。（JSONObject.java:159)at org.json.JSONObject。 Tarun

更改这两个线如下

public static final String sql_create="create table "+Table_name+"("+Name+" "+Type+","+Email+" "+Type+","+Pass+" "+Type+")"; 


public static final String sql_delete="drop table if exists " + DataBaseHelper.Table_name;

来源

2016-07-14 11:16:08 chetan

******************这个问题occour现在********************** ********** studentzone.studentzone E/AndroidRuntime：致命例外：main 进程：studentzone.studentzone，PID：31740 java.lang.IllegalStateException：无法在父级中找到方法reg（View）或祖先上下文的android：onClick属性定义在视图类android.support.v7.widget.AppCompatButton id为'button_register' – Tarun

先生请帮助我。我必须在明天之前提交作业 – Tarun

由于问题出在onClick事件上，因此我已经对我的申请 – Tarun

为什么我在这段代码中得到一个NullPointerException

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