我无法看到我的程序无效的原因。每当我尝试运行它时，它只会强行关闭。这是我的节目：
我的主要活动
package com.example.teacher;
public class MainActivity extends ActionBarActivity {
private DatabaseHelper dbHelper = new DatabaseHelper(MainActivity.this,"MyDatabase",2);
TextView text;
EditText txtPassword;
EditText teachersId;
EditText teachersName;
Button btnAdd;
Button btnDelete;
Button btnSearch;
Button btnPresent;
Button btnAbsent;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
text = (TextView) findViewById(R.id.textView1);
txtPassword = (EditText) findViewById(R.id.txtPassword);
teachersId = (EditText) findViewById(R.id.txtTeachersID);
teachersName = (EditText) findViewById(R.id.txtTeachersName);
btnPresent = (Button) findViewById(R.id.btnPresent);
btnAbsent = (Button) findViewById(R.id.btnAbsent);
btnAdd = (Button) findViewById(R.id.btnAddTeacher);
btnDelete = (Button) findViewById(R.id.btnDeleteTeacher);
SQLiteDatabase db = dbHelper.getWritableDatabase();
try
{
db.execSQL("create table Users(ID integer, name varchar(90), pass varchar(90), attendance varchar(30));");
text.setText("Successful in creating table.");
}
catch(Exception e)
{
text.setText("Error in creating table.");
e.printStackTrace();
}
btnAdd.setOnClickListener(new View.OnClickListener()
{
public void onClick(View v)
{
if("".equals(teachersId.getText().toString()) || "".equals(txtPassword.getText().toString()))
{
Toast toast = Toast.makeText(MainActivity.this,
"Something needs to be typed in.", Toast.LENGTH_LONG);
toast.show();
}
else
{
long flag = 0;
int id = 1;
SQLiteDatabase db = dbHelper.getWritableDatabase();
Cursor cursor = db.query("Users", new String[]{"count(*) ID"}, null, null, null, null, null);
while(cursor.moveToNext())
{
int idFromDatabase = cursor.getInt(cursor.getColumnIndex("ID"));
if(idFromDatabase != 0)
{
id = 1 + idFromDatabase;
}
}
ContentValues values = new ContentValues();
values.put("ID", Integer.parseInt(teachersId.getText().toString().trim()));
values.put("name", teachersName.getText().toString().trim());
values.put("pass", txtPassword.getText().toString().trim());
flag = db.insert("Users", null, values);
if(flag != -1)
{
Toast toast = Toast.makeText(MainActivity.this, "A new record has been added! "
, Toast.LENGTH_LONG);
toast.show();
db.close();
return;
}
else
{
Toast toast = Toast.makeText(MainActivity.this, "Something went wrong please check.",
Toast.LENGTH_LONG);
toast.show();
db.close();
return;
}
}
}
});
btnSearch.setOnClickListener(new View.OnClickListener()
{
public void onClick(View v)
{
if("".equals(teachersId.getText().toString()))
{
Toast toast = Toast.makeText(MainActivity.this, "What is the reference ID number?",
Toast.LENGTH_LONG);
toast.show();
return;
}
SQLiteDatabase db = dbHelper.getWritableDatabase();
Cursor cursor = db.query("Users", new String[]{"ID","name","pass"}, "ID=?",
new String[]{teachersId.getText().toString()}, null, null, null);
if (!cursor.moveToNext())
{
Toast toast = Toast.makeText(MainActivity.this, "The ID is not existing!",
Toast.LENGTH_LONG);
toast.show();
return;
}
cursor.moveToPrevious();
while(cursor.moveToNext())
{
int ID = cursor.getInt(cursor.getColumnIndex("ID"));
String name = cursor.getString(cursor.getColumnIndex("name"));
String password = cursor.getString(cursor.getColumnIndex("pass"));
teachersName.setText(name);
txtPassword.setText(password);
}
}
});
btnDelete.setOnClickListener(new View.OnClickListener()
{
public void onClick(View v)
{
int flag = 0;
SQLiteDatabase db = dbHelper.getWritableDatabase();
flag = db.delete("Users", "ID=?", new String[]{""+teachersId.getText().toString().trim()});
if(flag != 0)
{
Toast toast = Toast.makeText(MainActivity.this, "The record has been deleted! ",
Toast.LENGTH_LONG);
toast.show();
db.close();
return;
}
else
{
Toast toast = Toast.makeText(MainActivity.this, "Failed deleting the record! ",
Toast.LENGTH_LONG);
toast.show();
db.close();
return;
}
} });
//--------------------------------------------------
}
}
//--------------------------------------------------
我的活动主页
<LinearLayout 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:orientation='vertical'
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.example.teacher.MainActivity$PlaceholderFragment" >
<TextView
android:id="@+id/text"
android:layout_width="279dp"
android:layout_height="wrap_content"
android:text="@string/a" />
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="vertical" >
<TextView
android:id="@+id/textView2"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="@string/teachersID" />
<EditText
android:id="@+id/txtTeachersID"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:ems="10"
android:inputType="number" >
<requestFocus />
</EditText>
</LinearLayout>
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="vertical" >
<TextView
android:id="@+id/textView1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="@string/teachersName" />
<EditText
android:id="@+id/txtTeachersName"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:ems="10" android:inputType=""/>
</LinearLayout>
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="vertical" >
<TextView
android:id="@+id/textView3"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="@string/password" />
<EditText
android:id="@+id/txtPassword"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:ems="10"
android:inputType="textPassword" />
</LinearLayout>
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content" >
<Button
android:id="@+id/btnPresent"
android:layout_width="136dp"
android:layout_height="wrap_content"
android:text="@string/present" />
<Button
android:id="@+id/btnAbsent"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="@string/absent" />
</LinearLayout>
<Button
android:id="@+id/btnAddTeacher"
android:layout_width="285dp"
android:layout_height="wrap_content"
android:text="@string/addTeacher" />
<Button
android:id="@+id/btnDeleteTeacher"
android:layout_width="284dp"
android:layout_height="wrap_content"
android:text="@string/asadasda" />
<Button
android:id="@+id/btnCheckTeacher"
android:layout_width="281dp"
android:layout_height="wrap_content"
android:text="@string/browseTeacher" />
</LinearLayout>
我的dbhelper
package com.example.teacher;
public class DatabaseHelper extends SQLiteOpenHelper
{
public DatabaseHelper(Context context, String name, CursorFactory factory,
int version) {
super(context, name, factory, version);
// TODO Auto-generated constructor stub
}
private static final int VERSION = 1;
public DatabaseHelper(Context context,String name)
{
this(context,name,VERSION);
}
public DatabaseHelper(Context context,String name,int version)
{
this(context, name,null,version);
}
@Override
public void onCreate(SQLiteDatabase db)
{
//do nothing
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion)
{
// do nothing
}
}
根据logcat，它是由null异常引起的，但我真的不知道它在哪里以及如何处理它。请帮助解决这个力量关闭问题
05-15 04:22:20.579: E/AndroidRuntime(1067): FATAL EXCEPTION: main
05-15 04:22:20.579: E/AndroidRuntime(1067): Process: com.example.teacher, PID: 1067
05-15 04:22:20.579: E/AndroidRuntime(1067): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.teacher/com.example.teacher.MainActivity}: java.lang.NullPointerException
05-15 04:22:20.579: E/AndroidRuntime(1067): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2195)
05-15 04:22:20.579: E/AndroidRuntime(1067): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
05-15 04:22:20.579: E/AndroidRuntime(1067): at android.app.ActivityThread.access$800(ActivityThread.java:135)
05-15 04:22:20.579: E/AndroidRuntime(1067): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
05-15 04:22:20.579: E/AndroidRuntime(1067): at android.os.Handler.dispatchMessage(Handler.java:102)
05-15 04:22:20.579: E/AndroidRuntime(1067): at android.os.Looper.loop(Looper.java:136)
05-15 04:22:20.579: E/AndroidRuntime(1067): at android.app.ActivityThread.main(ActivityThread.java:5017)
05-15 04:22:20.579: E/AndroidRuntime(1067): at java.lang.reflect.Method.invokeNative(Native Method)
05-15 04:22:20.579: E/AndroidRuntime(1067): at java.lang.reflect.Method.invoke(Method.java:515)
05-15 04:22:20.579: E/AndroidRuntime(1067): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
05-15 04:22:20.579: E/AndroidRuntime(1067): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
05-15 04:22:20.579: E/AndroidRuntime(1067): at dalvik.system.NativeStart.main(Native Method)
05-15 04:22:20.579: E/AndroidRuntime(1067): Caused by: java.lang.NullPointerException
05-15 04:22:20.579: E/AndroidRuntime(1067): at com.example.teacher.MainActivity.onCreate(MainActivity.java:112)
05-15 04:22:20.579: E/AndroidRuntime(1067): at android.app.Activity.performCreate(Activity.java:5231)
05-15 04:22:20.579: E/AndroidRuntime(1067): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
05-15 04:22:20.579: E/AndroidRuntime(1067): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2159)
05-15 04:22:20.579: E/AndroidRuntime(1067): ... 11 more
05-15 04:22:22.909: I/Process(1067): Sending signal. PID: 1067 SIG: 9
答案 0 :(得分：3)
您尚未初始化btnSearch
将此添加到onCreate
btnSearch= (Button) findViewById(R.id.idForSearchButton);
我认为可能是R.id.btnCheckTeacher