首先，我知道NullPointerException的含义是什么，我检查了有关该主题的类似问题，但没有任何帮助。
MainActivity.java
public class MainActivity extends AppCompatActivity
{
private TextView enterNumberOfFloorsTextView;
private EditText numberOfFloorsEditText;
private Button goToFloorsActivityButton;
@Override
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
initializeView();
goToFloorsActivityButton.setOnClickListener(new View.OnClickListener()
{
@Override
public void onClick(View v)
{
Intent intent = new Intent(MainActivity.this, FloorActivity.class);
intent.putExtra("NumberOfFloors",numberOfFloorsEditText.getText().toString());
startActivity(intent);
}
});
}
public void initializeView()
{
enterNumberOfFloorsTextView = (TextView) findViewById(R.id.enter_number_of_floors_text_view_id);
numberOfFloorsEditText = (EditText) findViewById(R.id.number_of_floors_edit_text_id);
goToFloorsActivityButton = (Button) findViewById(R.id.go_to_floors_activity_button_id);
}
}
我初始化了按钮，我也检查了它不是null。所以它绝对不是空的。
我认为问题出在清单或我想要开始的活动中。
也许LogCat可以提供帮助。
logcat的
02-16 15:37:48.788: E/SQLiteLog(3461): (1) near "EXIST": syntax error
02-16 15:37:48.792: E/AndroidRuntime(3461): FATAL EXCEPTION: main
02-16 15:37:48.792: E/AndroidRuntime(3461): Process: com.dl.my.lift.bag.liftmybag, PID: 3461
02-16 15:37:48.792: E/AndroidRuntime(3461): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.dl.my.lift.bag.liftmybag/com.dl.my.lift.bag.liftmybag.FloorActivity}: android.database.sqlite.SQLiteException: near "EXIST": syntax error (code 1): , while compiling: DROP TABLE IF EXIST floorsTable
02-16 15:37:48.792: E/AndroidRuntime(3461): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2305)
02-16 15:37:48.792: E/AndroidRuntime(3461): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2365)
02-16 15:37:48.792: E/AndroidRuntime(3461): at android.app.ActivityThread.access$800(ActivityThread.java:148)
02-16 15:37:48.792: E/AndroidRuntime(3461): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1283)
02-16 15:37:48.792: E/AndroidRuntime(3461): at android.os.Handler.dispatchMessage(Handler.java:102)
02-16 15:37:48.792: E/AndroidRuntime(3461): at android.os.Looper.loop(Looper.java:135)
02-16 15:37:48.792: E/AndroidRuntime(3461): at android.app.ActivityThread.main(ActivityThread.java:5272)
02-16 15:37:48.792: E/AndroidRuntime(3461): at java.lang.reflect.Method.invoke(Native Method)
02-16 15:37:48.792: E/AndroidRuntime(3461): at java.lang.reflect.Method.invoke(Method.java:372)
02-16 15:37:48.792: E/AndroidRuntime(3461): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:909)
02-16 15:37:48.792: E/AndroidRuntime(3461): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:704)
02-16 15:37:48.792: E/AndroidRuntime(3461): Caused by: android.database.sqlite.SQLiteException: near "EXIST": syntax error (code 1): , while compiling: DROP TABLE IF EXIST floorsTable
02-16 15:37:48.792: E/AndroidRuntime(3461): at android.database.sqlite.SQLiteConnection.nativePrepareStatement(Native Method)
02-16 15:37:48.792: E/AndroidRuntime(3461): at android.database.sqlite.SQLiteConnection.acquirePreparedStatement(SQLiteConnection.java:894)
02-16 15:37:48.792: E/AndroidRuntime(3461): at android.database.sqlite.SQLiteConnection.prepare(SQLiteConnection.java:505)
02-16 15:37:48.792: E/AndroidRuntime(3461): at android.database.sqlite.SQLiteSession.prepare(SQLiteSession.java:726)
02-16 15:37:48.792: E/AndroidRuntime(3461): at android.database.sqlite.SQLiteProgram.<init>(SQLiteProgram.java:58)
02-16 15:37:48.792: E/AndroidRuntime(3461): at android.database.sqlite.SQLiteStatement.<init>(SQLiteStatement.java:31)
02-16 15:37:48.792: E/AndroidRuntime(3461): at android.database.sqlite.SQLiteDatabase.executeSql(SQLiteDatabase.java:1775)
02-16 15:37:48.792: E/AndroidRuntime(3461): at android.database.sqlite.SQLiteDatabase.execSQL(SQLiteDatabase.java:1706)
02-16 15:37:48.792: E/AndroidRuntime(3461): at com.dl.my.lift.bag.liftmybag.FloorsDatabase.onUpgrade(FloorsDatabase.java:50)
02-16 15:37:48.792: E/AndroidRuntime(3461): at android.database.sqlite.SQLiteOpenHelper.getDatabaseLocked(SQLiteOpenHelper.java:256)
02-16 15:37:48.792: E/AndroidRuntime(3461): at android.database.sqlite.SQLiteOpenHelper.getWritableDatabase(SQLiteOpenHelper.java:163)
02-16 15:37:48.792: E/AndroidRuntime(3461): at com.dl.my.lift.bag.liftmybag.FloorsDatabase.getAllFloors(FloorsDatabase.java:120)
02-16 15:37:48.792: E/AndroidRuntime(3461): at com.dl.my.lift.bag.liftmybag.FloorActivity.onCreate(FloorActivity.java:51)
02-16 15:37:48.792: E/AndroidRuntime(3461): at android.app.Activity.performCreate(Activity.java:5977)
02-16 15:37:48.792: E/AndroidRuntime(3461): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1105)
02-16 15:37:48.792: E/AndroidRuntime(3461): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2258)
02-16 15:37:48.792: E/AndroidRuntime(3461): ... 10 more
activity_main.xml中
<?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:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context="com.dl.my.lift.bag.liftmybag.MainActivity">
<TextView
android:id="@+id/enter_number_of_floors_text_view_id"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="@string/enter_number_of_floors_text_view_text"
android:textAllCaps="false"
/>
<EditText
android:id="@+id/number_of_floors_edit_text_id"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:width="40dp"
android:layout_below="@id/enter_number_of_floors_text_view_id"
/>
<Button
android:id="@+id/go_to_floors_activity_button_id"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="@string/go_to_floors_activity_button_text"
android:textAllCaps="false"
android:layout_below="@id/number_of_floors_edit_text_id"
/>
</RelativeLayout>
清单
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.dl.my.lift.bag.liftmybag">
<uses-permission android:name="android.permission.SEND_SMS" />
<uses-permission android:name="android.permission.INTERNET" />
<application
android:allowBackup="true"
android:icon="@mipmap/ic_launcher"
android:label="@string/app_name"
android:supportsRtl="true"
android:theme="@style/AppTheme">
<activity android:name=".MainActivity">
<intent-filter>
<category android:name="android.intent.category.LAUNCHER" />
<action android:name="android.intent.action.MAIN" />
</intent-filter>
</activity>
<activity android:name=".FloorActivity"></activity>
</application>
</manifest>
问题在于，我在应用程序上有一个工作Sqlite数据库，然后我从主要活动中删除了他并将所有代码（初始化过程和向某些表添加行）放到活动中我要开始。然后我写了这个MainActivity，曾经是一个工作的数据库。
也许那是什么造成了所有麻烦？
修改
我编辑了logcat。它确实说了Sqlite。
EDIT2 FloorAcivity.java
package com.dl.my.lift.bag.liftmybag;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.telephony.SmsManager;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import java.util.ArrayList;
import java.util.List;
public class FloorActivity extends AppCompatActivity implements View.OnClickListener
{
private Button floor12Button;
private Button floor11Button;
private Button floor10Button;
private Button floor9Button;
private Button floor8Button;
private Button floor7Button;
private Button floor6Button;
private Button floor5Button;
private Button floor4Button;
private Button floor3Button;
private Button floor2Button;
private Button floor1Button;
private SmsManager smsManager;
private static final String SOMETHING_WENT_WRONG_TAG = "Something went wrong";
List<Floor> floors;
FloorsDatabase floorsDatabase;
@Override
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_floor);
initializeView();
setOnClickListeners();
smsManager = SmsManager.getDefault();
floorsDatabase = new FloorsDatabase(FloorActivity.this);
//floorsDatabase.addFloor(new Floor(2.2,7,"","Nothing special"));
floors = new ArrayList<Floor>();
floors = floorsDatabase.getAllFloors();
for (Floor floor : floors) // For each floor in floors
{
floor1Button.setText(floors.toString());
}
}
public void initializeView()
{
floor12Button = (Button) findViewById(R.id.button_1_id);
floor11Button = (Button) findViewById(R.id.button_2_id);
floor10Button = (Button) findViewById(R.id.button_3_id);
floor9Button = (Button) findViewById(R.id.button_4_id);
floor8Button = (Button) findViewById(R.id.button_5_id);
floor7Button = (Button) findViewById(R.id.button_6_id);
floor6Button = (Button) findViewById(R.id.button_7_id);
floor5Button = (Button) findViewById(R.id.button_8_id);
floor4Button = (Button) findViewById(R.id.button_9_id);
floor3Button = (Button) findViewById(R.id.button_10_id);
floor2Button = (Button) findViewById(R.id.button_11_id);
floor1Button = (Button) findViewById(R.id.button_12_id);
}
public void setOnClickListeners()
{
this.floor12Button.setOnClickListener(this);
this.floor11Button.setOnClickListener(this);
this.floor10Button.setOnClickListener(this);
this.floor9Button.setOnClickListener(this);
this.floor8Button.setOnClickListener(this);
this.floor7Button.setOnClickListener(this);
this.floor6Button.setOnClickListener(this);
this.floor5Button.setOnClickListener(this);
this.floor4Button.setOnClickListener(this);
this.floor3Button.setOnClickListener(this);
this.floor2Button.setOnClickListener(this);
this.floor1Button.setOnClickListener(this);
}
@Override
public void onClick(View v)
{
int buttonId = v.getId();
switch (buttonId)
{
case R.id.button_1_id: // Floor 12
{
this.smsManager.sendTextMessage("+972523508838",null,"Hi Kids",null,null); // Send SMS to a phone number
break;
}
case R.id.button_2_id: // Floor 11
{
this.smsManager.sendTextMessage("+972523508838",null,"Hi Kids",null,null); // Send SMS to a phone number
break;
}
case R.id.button_3_id: // Floor 10
{
this.smsManager.sendTextMessage("+972523508838",null,"Hi Kids",null,null); // Send SMS to a phone number
break;
}
case R.id.button_4_id: // Floor 9
{
this.smsManager.sendTextMessage("+972523508838",null,"Hi Kids",null,null); // Send SMS to a phone number
break;
}
case R.id.button_5_id: // Floor 8
{
this.smsManager.sendTextMessage("+972523508838",null,"Hi Kids",null,null); // Send SMS to a phone number
break;
}
case R.id.button_6_id: // Floor 7
{
this.smsManager.sendTextMessage("+972523508838",null,"Hi Kids",null,null); // Send SMS to a phone number
break;
}
case R.id.button_7_id: // Floor 6
{
this.smsManager.sendTextMessage("+972523508838",null,"Hi Kids",null,null); // Send SMS to a phone number
break;
}
case R.id.button_8_id: // Floor 5
{
this.smsManager.sendTextMessage("+972523508838",null,"Hi Kids",null,null); // Send SMS to a phone number
break;
}
case R.id.button_9_id: // Floor 4
{
this.smsManager.sendTextMessage("+972523508838",null,"Hi Kids",null,null); // Send SMS to a phone number
break;
}
case R.id.button_10_id: // Floor 3
{
this.smsManager.sendTextMessage("+972523508838",null,"Hi Kids",null,null); // Send SMS to a phone number
break;
}
case R.id.button_11_id: // Floor 2
{
this.smsManager.sendTextMessage("+972523508838",null,"Hi Kids",null,null); // Send SMS to a phone number
break;
}
case R.id.button_12_id: // Floor 1
{
this.smsManager.sendTextMessage("+972523508838",null,"Hi Kids",null,null); // Send SMS to a phone number
break;
}
default:
{
Log.i(SOMETHING_WENT_WRONG_TAG,"Something went wrong");
break;
}
}
}
}