每次我运行我的应用程序时，Null Pointer 都会在 logcat 上投射，我怎么知道错误在哪里？
这是最初的logcat错误我发现的错误是不存在这样的列我已经修复了它现在这是错误：
02-12 00:16:40.837: D/AndroidRuntime(360): Shutting down VM
02-12 00:16:40.837: W/dalvikvm(360): threadid=1: thread exiting with uncaught exception (group=0x40015560)
02-12 00:16:40.868: E/AndroidRuntime(360): FATAL EXCEPTION: main
02-12 00:16:40.868: E/AndroidRuntime(360): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.database/com.example.database.AndroidSQLite}: java.lang.NullPointerException
02-12 00:16:40.868: E/AndroidRuntime(360): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1647)
02-12 00:16:40.868: E/AndroidRuntime(360): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1663)
02-12 00:16:40.868: E/AndroidRuntime(360): at android.app.ActivityThread.access$1500(ActivityThread.java:117)
02-12 00:16:40.868: E/AndroidRuntime(360): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:931)
02-12 00:16:40.868: E/AndroidRuntime(360): at android.os.Handler.dispatchMessage(Handler.java:99)
02-12 00:16:40.868: E/AndroidRuntime(360): at android.os.Looper.loop(Looper.java:123)
02-12 00:16:40.868: E/AndroidRuntime(360): at android.app.ActivityThread.main(ActivityThread.java:3683)
02-12 00:16:40.868: E/AndroidRuntime(360): at java.lang.reflect.Method.invokeNative(Native Method)
02-12 00:16:40.868: E/AndroidRuntime(360): at java.lang.reflect.Method.invoke(Method.java:507)
02-12 00:16:40.868: E/AndroidRuntime(360): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
02-12 00:16:40.868: E/AndroidRuntime(360): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
02-12 00:16:40.868: E/AndroidRuntime(360): at dalvik.system.NativeStart.main(Native Method)
02-12 00:16:40.868: E/AndroidRuntime(360): Caused by: java.lang.NullPointerException
02-12 00:16:40.868: E/AndroidRuntime(360): at com.example.database.AndroidSQLite.onCreate(AndroidSQLite.java:58)
02-12 00:16:40.868: E/AndroidRuntime(360): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
02-12 00:16:40.868: E/AndroidRuntime(360): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1611)
02-12 00:16:40.868: E/AndroidRuntime(360): ... 11 more
02-12 00:16:42.977: I/Process(360): Sending signal. PID: 360 SIG: 9
这是我的代码：
package com.example.database;
import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.database.sqlite.SQLiteDatabase.CursorFactory;
public class SQLiteAdapter {
public static final String MYDATABASE_NAME = "SCORING";
public static final String MYDATABASE_TABLE = "SCORING_TABLE";
public static final int MYDATABASE_VERSION = 3;
public static final String KEY_ID = "_id";
public static final String KEY_CONTENT1 = "Content1";
public static final String KEY_CONTENT2 = "Content2";
public static final String KEY_CONTENT3 = "Content3";
//create table SCORING (ID integer primary key, Content text not null);
private static final String SCRIPT_CREATE_DATABASE =
"create table " + MYDATABASE_TABLE + " ("
+ KEY_ID + " integer primary key autoincrement, "
+ KEY_CONTENT1 + " text not null, "
+ KEY_CONTENT2 + " text not null, "
+ KEY_CONTENT3 + "text not null);";
private SQLiteHelper sqLiteHelper;
private SQLiteDatabase sqLiteDatabase;
private Context context;
public SQLiteAdapter(Context c){
context = c;
}
public SQLiteAdapter openToRead() throws android.database.SQLException {
sqLiteHelper = new SQLiteHelper(context, MYDATABASE_NAME, null, MYDATABASE_VERSION);
sqLiteDatabase = sqLiteHelper.getReadableDatabase();
return this;
}
public SQLiteAdapter openToWrite() throws android.database.SQLException {
sqLiteHelper = new SQLiteHelper(context, MYDATABASE_NAME, null, MYDATABASE_VERSION);
sqLiteDatabase = sqLiteHelper.getWritableDatabase();
return this;
}
public void close(){
sqLiteHelper.close();
}
public long insert(String content1, String content2, String content3){
ContentValues contentValues = new ContentValues();
contentValues.put(KEY_CONTENT1, content1);
contentValues.put(KEY_CONTENT2, content2);
contentValues.put(KEY_CONTENT3, content3);
return sqLiteDatabase.insert(MYDATABASE_TABLE, null, contentValues);
}
public int deleteAll(){
return sqLiteDatabase.delete(MYDATABASE_TABLE, null, null);
}
public Cursor queueAll(){
String[] columns = new String[]{KEY_ID, KEY_CONTENT1, KEY_CONTENT2, KEY_CONTENT3};
Cursor cursor = sqLiteDatabase.query(MYDATABASE_TABLE, columns,
null, null, null, null, null);
return cursor;
}
public class SQLiteHelper extends SQLiteOpenHelper {
public SQLiteHelper(Context context, String name,
CursorFactory factory, int version) {
super(context, name, factory, version);
}
@Override
public void onCreate(SQLiteDatabase db) {
// TODO Auto-generated method stub
db.execSQL(SCRIPT_CREATE_DATABASE);
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
// TODO Auto-generated method stub
// If you need to add a column
if (newVersion > oldVersion) {
db.execSQL("ALTER TABLE SCORING_TABLE ADD COLUMN Content4 TEXT");
}
}
}
}
现在我在这部分遇到了第二个错误
02-12 00:54:03.516: D/AndroidRuntime(359): Shutting down VM
02-12 00:54:03.516: W/dalvikvm(359): threadid=1: thread exiting with uncaught exception (group=0x40015560)
02-12 00:54:03.546: E/AndroidRuntime(359): FATAL EXCEPTION: main
02-12 00:54:03.546: E/AndroidRuntime(359): java.lang.ArrayIndexOutOfBoundsException
02-12 00:54:03.546: E/AndroidRuntime(359): at android.widget.SimpleCursorAdapter.bindView(SimpleCursorAdapter.java:130)
02-12 00:54:03.546: E/AndroidRuntime(359): at android.widget.CursorAdapter.getView(CursorAdapter.java:186)
02-12 00:54:03.546: E/AndroidRuntime(359): at android.widget.AbsListView.obtainView(AbsListView.java:1430)
02-12 00:54:03.546: E/AndroidRuntime(359): at android.widget.ListView.makeAndAddView(ListView.java:1745)
02-12 00:54:03.546: E/AndroidRuntime(359): at android.widget.ListView.fillDown(ListView.java:670)
02-12 00:54:03.546: E/AndroidRuntime(359): at android.widget.ListView.fillFromTop(ListView.java:727)
02-12 00:54:03.546: E/AndroidRuntime(359): at android.widget.ListView.layoutChildren(ListView.java:1584)
02-12 00:54:03.546: E/AndroidRuntime(359): at android.widget.AbsListView.onLayout(AbsListView.java:1260)
02-12 00:54:03.546: E/AndroidRuntime(359): at android.view.View.layout(View.java:7175)
02-12 00:54:03.546: E/AndroidRuntime(359): at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1254)
02-12 00:54:03.546: E/AndroidRuntime(359): at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1130)
02-12 00:54:03.546: E/AndroidRuntime(359): at android.widget.LinearLayout.onLayout(LinearLayout.java:1047)
02-12 00:54:03.546: E/AndroidRuntime(359): at android.view.View.layout(View.java:7175)
02-12 00:54:03.546: E/AndroidRuntime(359): at android.widget.FrameLayout.onLayout(FrameLayout.java:338)
02-12 00:54:03.546: E/AndroidRuntime(359): at android.view.View.layout(View.java:7175)
02-12 00:54:03.546: E/AndroidRuntime(359): at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1254)
02-12 00:54:03.546: E/AndroidRuntime(359): at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1130)
02-12 00:54:03.546: E/AndroidRuntime(359): at android.widget.LinearLayout.onLayout(LinearLayout.java:1047)
02-12 00:54:03.546: E/AndroidRuntime(359): at android.view.View.layout(View.java:7175)
02-12 00:54:03.546: E/AndroidRuntime(359): at android.widget.FrameLayout.onLayout(FrameLayout.java:338)
02-12 00:54:03.546: E/AndroidRuntime(359): at android.view.View.layout(View.java:7175)
02-12 00:54:03.546: E/AndroidRuntime(359): at android.view.ViewRoot.performTraversals(ViewRoot.java:1140)
02-12 00:54:03.546: E/AndroidRuntime(359): at android.view.ViewRoot.handleMessage(ViewRoot.java:1859)
02-12 00:54:03.546: E/AndroidRuntime(359): at android.os.Handler.dispatchMessage(Handler.java:99)
02-12 00:54:03.546: E/AndroidRuntime(359): at android.os.Looper.loop(Looper.java:123)
02-12 00:54:03.546: E/AndroidRuntime(359): at android.app.ActivityThread.main(ActivityThread.java:3683)
02-12 00:54:03.546: E/AndroidRuntime(359): at java.lang.reflect.Method.invokeNative(Native Method)
02-12 00:54:03.546: E/AndroidRuntime(359): at java.lang.reflect.Method.invoke(Method.java:507)
02-12 00:54:03.546: E/AndroidRuntime(359): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
02-12 00:54:03.546: E/AndroidRuntime(359): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
02-12 00:54:03.546: E/AndroidRuntime(359): at dalvik.system.NativeStart.main(Native Method)
02-12 00:54:05.646: I/Process(359): Sending signal. PID: 359 SIG: 9
及其类：
package com.example.database;
import com.example.database.R;
import android.app.Activity;
import android.content.Intent;
import android.database.Cursor;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ListView;
import android.widget.SimpleCursorAdapter;
import android.widget.TextView;
import android.widget.Toast;
public class AndroidSQLite extends Activity {
EditText inputContent2;
TextView textView1, textView2;
Button buttonAdd, buttonDeleteAll;
private SQLiteAdapter mySQLiteAdapter;
ListView listContent;
SimpleCursorAdapter cursorAdapter;
Cursor cursor;
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
textView1 = (TextView)findViewById(R.id.textView1);
textView2 = (TextView)findViewById(R.id.textView2);
inputContent2 = (EditText)findViewById(R.id.content2);
buttonAdd = (Button)findViewById(R.id.add);
buttonDeleteAll = (Button)findViewById(R.id.deleteall);
listContent = (ListView)findViewById(R.id.contentlist);
mySQLiteAdapter = new SQLiteAdapter(this);
mySQLiteAdapter.openToWrite();
cursor = mySQLiteAdapter.queueAll();
String[] from = new String[]{SQLiteAdapter.KEY_ID, SQLiteAdapter.KEY_CONTENT1, SQLiteAdapter.KEY_CONTENT2};
int[] to = new int[]{R.id.id, R.id.text1, R.id.text2, R.id.text3};
cursorAdapter =
new SimpleCursorAdapter(this, R.layout.row, cursor, from, to);
listContent.setAdapter(cursorAdapter);
buttonAdd.setOnClickListener(buttonAddOnClickListener);
buttonDeleteAll.setOnClickListener(buttonDeleteAllOnClickListener);
}
Button.OnClickListener buttonAddOnClickListener
= new Button.OnClickListener(){
@Override
public void onClick(View arg0) {
// TODO Auto-generated method stub
int a=Integer.parseInt(textView1.getText().toString());
int b=a+2;
String s1 = String.valueOf(b);
textView1.setText(s1);
Toast.makeText(getApplicationContext(), "Wrong",
Toast.LENGTH_SHORT).show();
String data1 = textView1.getText().toString();
String data2 = inputContent2.getText().toString();
String data3 = textView2.getText().toString();
mySQLiteAdapter.insert(data1, data2, data3);
updateList();
}
};
Button.OnClickListener buttonDeleteAllOnClickListener
= new Button.OnClickListener(){
@Override
public void onClick(View arg0) {
// TODO Auto-generated method stub
mySQLiteAdapter.deleteAll();
updateList();
}
};
@Override
protected void onDestroy() {
// TODO Auto-generated method stub
super.onDestroy();
mySQLiteAdapter.close();
}
private void updateList(){
cursor.requery();
}
}
至于这里的xml布局是：
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
>
<TextView
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="hello"
/>
<TextView
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="Enter content of column 1"
/>
<TextView
android:id="@+id/textView1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="0"
android:textAppearance="?android:attr/textAppearanceLarge" />
<TextView
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="Enter content of column 2"
/>
<EditText
android:id="@+id/content2"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
/>
<TextView
android:id="@+id/textView2"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Large Text"
android:textAppearance="?android:attr/textAppearanceLarge" />
<Button
android:id="@+id/add"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="Add"
/>
<Button
android:id="@+id/deleteall"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="Delete All"
/>
<ListView
android:id="@+id/contentlist"
android:layout_width="fill_parent"
android:layout_height="fill_parent"/>
</LinearLayout>