Question

btnAdd应该打开SecondActivity，它会收集一个新的电子邮件地址并将其返回到第一个Activity并存储在数组中。然后它将添加新的电子邮件地址以显示在ListView中此外，每次我打开应用程序时，它会一直附加到列表中，如果我从4个电子邮件地址开始，每次运行应用程序时，它都会添加到它中，从而给出了这个错误。

MainActivity.java

public class MainActivity extends ActionBarActivity { 

DBAdapter db;    
ListView listContacts;    
Button btnAdd;    
int selectedItem = 0;    
String name, email;    

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

    listContacts = (ListView)findViewById(R.id.listContacts);
    btnAdd = (Button)findViewById(R.id.btnAdd);
    btnAdd.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
       // Start 2nd Activity
       startActivity(new Intent("ca.nbcc.lizgoldston.SecondActivity"));
       finish();
       if(selectedItem != 0){
                insertContact(name, email);
            }
        }
    });

    db = new DBAdapter(this);   // Set up our DBHelper
        addContacts();              // Add some generic data to DB for   display purposes
    listContacts();             // Display the records in a ListView

    // Set the Listener on the ListView and change background color for selected item
    listContacts.setOnItemClickListener(new AdapterView.OnItemClickListener() {
        @Override
        public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
            listContacts.setBackgroundColor(Color.WHITE);
            listContacts.getChildAt(position).setBackgroundColor(Color.GRAY);
            parent.getItemAtPosition(position); // Get the ListItem at position clicked
            listContacts.setSelection(position);
            listContacts.setSelected(true);
            String info = parent.getItemAtPosition(position).toString(); // Get the String with contact info
            int contactId = Integer.parseInt(info.substring(0,info.indexOf(":"))); // Parse for contact id
            selectedItem = contactId;  // Set the selectedItem id
            Toast.makeText(getApplicationContext(), info + " clicked", Toast.LENGTH_SHORT).show();
        }
    });

}

public void addContacts() {
    // Add some generic contact records for display purposes
    db.open();
    if (db.insertContact("Sally Brown", "sally@nbcc.ca") >= 0){
        Toast.makeText(this, "Add successful.", Toast.LENGTH_SHORT).show();
    }

    if (db.insertContact("John Smith", "john@nbcc.ca") >= 0) {
        Toast.makeText(this, "Add successful.", Toast.LENGTH_SHORT).show();
    }

    if (db.insertContact("Tom Brown", "tom@nbcc.ca") >= 0){
        Toast.makeText(this, "Add successful.", Toast.LENGTH_SHORT).show();
    }

    if (db.insertContact("Susie Brawn", "susie@nbcc.ca") >= 0){
        Toast.makeText(this, "Add successful.", Toast.LENGTH_SHORT).show();
    }
    db.close();
}

public void getContacts() {
    // Get all contacts
    db.open();
    Cursor c = db.getAllContacts();
    if (c.moveToFirst())  // As long as there are records
    {
        do {
            displayContact(c);
        } while (c.moveToNext());
    }
    db.close();
}

public Contact getContact(int _id) {
    // Get a contact based on id provided
    Contact contact = new Contact();
    db.open();
    Cursor c = db.getContact(_id);
    if (c.moveToFirst()){  // As long as there are records
        displayContact(c);  // Display the specific contact
        contact.setId(c.getInt(0));
        contact.setName(c.getString(1));
        contact.setEmail(c.getString(2));
    }
    else {
        Toast.makeText(this, "No contact found", Toast.LENGTH_LONG).show();
    }
    db.close();

    return contact;
}

// Method to update a contact with the info provided
public void updateContact(int _id, String _name, String _email) {
    // Update contact
    // This could obviously be made 'prettier' by adding confirmation dialog, etc.
    db.open();
    if (db.updateContact(_id, _name, _email)) {
    }else {
        Toast.makeText(this, "Update failed.", Toast.LENGTH_LONG).show();
    }
    db.close();
}

// Method to delete contact with the id provided
public void insertContact(String name, String email) {
    // Add Contact
    db.open();
    if (db.insertContact(name, email) == 1) {
        Toast.makeText(this, "Add successful.", Toast.LENGTH_LONG).show();
    }else {
        Toast.makeText(this, "Add failed.", Toast.LENGTH_LONG).show();
    }
    db.close();
}

public void displayContact(Cursor c)
{
    // Display specific Contact in the cursor provided
    Toast.makeText(this,
            "id: " + c.getInt(0) + "\n" +
                    "Name: " + c.getString(1) + "\n" +
                    "Email:  " + c.getString(2),
            Toast.LENGTH_LONG).show();
}

public void listContacts(){
    // Show the database contacts in a ListView
    List<String> contactList = getContactList();
    ArrayAdapter adapter = new ArrayAdapter(this,           android.R.layout.simple_list_item_1, contactList);
    listContacts.setAdapter(adapter);
}

public List<String> getContactList(){
    List<String> contactList = new ArrayList<String>();
    db.open();
    Cursor c = db.getAllContacts();
    if (c.moveToFirst())
    {
        do {
            contactList.add(c.getString(0) + ":" + c.getString(1) + ":" + c.getString(2));
        } while (c.moveToNext());
    }
    db.close();
    return contactList;
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.menu_main, menu);
    return true;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // Handle action bar item clicks here. The action bar will
    // automatically handle clicks on the Home/Up button, so long
    // as you specify a parent activity in AndroidManifest.xml.
    int id = item.getItemId();

    //noinspection SimplifiableIfStatement
    if (id == R.id.action_settings) {
        return true;
    }

    return super.onOptionsItemSelected(item);
}

Android清单

<application
    android:allowBackup="true"
    android:icon="@drawable/ic_launcher"
    android:label="@string/app_name"
    android:theme="@style/AppTheme" >
    <activity
        android:name=".MainActivity"
        android:label="@string/app_name" >
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />

            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>
    <activity
        android:name=".SecondActivity"
        android:label="@string/app_name" >
    </activity>

</application>

SecondActivity.java

public class SecondActivity extends ActionBarActivity {  

TextView txtEmail;        
EditText txtAddress;        
Button btnSave;        

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

    txtEmail = (TextView)findViewById(R.id.txtEmail);
    txtAddress = (EditText)findViewById(R.id.txtAddress);
    btnSave = (Button)findViewById(R.id.btnSave);
    btnSave.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            if (v == findViewById(R.id.btnSave)) {
                MainActivity main = new MainActivity();
                main.email = txtAddress.getText().toString();
            }
        }
    });
}


@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.menu_email, menu);
    return true;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // Handle action bar item clicks here. The action bar will
    // automatically handle clicks on the Home/Up button, so long
    // as you specify a parent activity in AndroidManifest.xml.
    int id = item.getItemId();    
    //noinspection SimplifiableIfStatement
    if (id == R.id.action_settings) {
        return true;
    }

    return super.onOptionsItemSelected(item);
}

DBAdapter.java

public class DBAdapter {  

static final String KEY_ROWID = "id";    
static final String KEY_NAME = "name";    
static final String KEY_EMAIL = "email";    
static final String TAG = "DBAdapter";    

static final String DATABASE_NAME = "MyDB";    
static final String DATABASE_TABLE = "contacts";    
static final int DATABASE_VERSION = 1;    

static final String DATABASE_CREATE =
        "CREATE TABLE contacts (id integer primary key autoincrement, "
                + "name text not null, email text not null);";


final Context context;
DatabaseHelper DBHelper;
SQLiteDatabase db;

public DBAdapter(Context _context){
    this.context = _context;
    DBHelper = new DatabaseHelper(context);
}

private static class DatabaseHelper extends SQLiteOpenHelper {
    DatabaseHelper(Context context) {
        super(context, DATABASE_NAME, null, DATABASE_VERSION);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        try {
            db.execSQL(DATABASE_CREATE);
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        Log.w(TAG, "Upgrading database from version " + oldVersion + " to "
                + newVersion + ". This will destroy all old data");
        db.execSQL("DROP TABLE IF EXISTS contacts");
        onCreate(db);
    }

    @Override
    public void onDowngrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        Log.w(TAG, "Downgrading database from version " + oldVersion + " to "
                + newVersion + ". This will destroy all old data");
        db.execSQL("DROP TABLE IF EXISTS contacts");
        onCreate(db);
    }
}

// Open the db
public DBAdapter open() throws SQLException{
    db = DBHelper.getWritableDatabase();
    return this;
}

// Closes the db
public void close(){
    DBHelper.close();
}

// Insert a new contact
public long insertContact(String name, String email){
    ContentValues initialValues = new ContentValues();
    initialValues.put(KEY_NAME, name);
    initialValues.put(KEY_EMAIL, email);
    return db.insert(DATABASE_TABLE, null, initialValues);
}

// Deletes a specific contact
public boolean deleteContact(long rowId){
    return db.delete(DATABASE_TABLE, KEY_ROWID + "=" + rowId, null) > 0;
}

// Getting All Contacts in a List
public List<Contact> getAllContactsList() {
    List<Contact> contactList = new ArrayList<Contact>();
    // Select All Query
    String selectQuery = "SELECT  * FROM contacts";
    Cursor cursor = db.rawQuery(selectQuery, null);

    // looping through all rows and adding to list
    if (cursor.moveToFirst()) {
        do {
            Contact contact = new Contact();
            contact.setId(Integer.parseInt(cursor.getString(0)));
            contact.setName(cursor.getString(1));
            contact.setEmail(cursor.getString(2));

            // Adding contact to list
            contactList.add(contact);
        } while (cursor.moveToNext());
    }
    // return contact list
    return contactList;
}

// Retrieve all contacts
public Cursor getAllContacts(){
    return db.query(DATABASE_TABLE, new String[] {KEY_ROWID, KEY_NAME,
            KEY_EMAIL}, null, null, null, null, null);
}

// Retrieve a specific contact
public Cursor getContact(long rowId) throws SQLException{
    Cursor mCursor =
            db.query(true, DATABASE_TABLE, new String[] {KEY_ROWID,
                            KEY_NAME, KEY_EMAIL}, KEY_ROWID + "=" + rowId, null,
                    null, null, null, null);
    if (mCursor != null) {
        mCursor.moveToFirst();
    }
    return mCursor;
}

// Update a contact
public boolean updateContact(long rowId, String name,
         String email){
    ContentValues args = new ContentValues();
    args.put(KEY_NAME, name);
    args.put(KEY_EMAIL, email);
    return db.update(DATABASE_TABLE, args, KEY_ROWID + "=" + rowId, null) > 0;
}

Contact.java

public class Contact {    

private int id;        
private String name;        
private String email;    

public int getId() {    
    return id;    
}

public void setId(int id) {
    this.id = id;
}

public String getName() {
    return name;
}

public void setName(String name) {
    this.name = name;
}

public String getEmail() {
    return email;
}

public void setEmail(String email) {
    this.email = email;
}

activity_main.xml中

<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: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=".MainActivity"    
android:orientation="vertical">    

<TextView
    android:text="Email Addresses..."
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:id="@+id/textView"  />

<ListView
    android:id="@+id/listContacts"
    android:layout_width="fill_parent"
    android:layout_height="450dp"
    android:layout_below="@+id/textView"  />

<Button
    android:id="@+id/btnAdd"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="Add"
    android:layout_below="@+id/listContacts"
    android:layout_gravity="bottom" />
</LinearLayout>

activity_secondactivity.xml

<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: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="ca.nbcc.lizgoldston.emaillistapp.email"    
android:orientation="vertical"    
android:clickable="true">    

<TextView
    android:id="@+id/txtEmail"
    android:text="Add a new email... "
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"/>

<EditText
    android:id="@+id/txtAddress"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="enter a new email here"
    android:inputType="textEmailAddress"
    android:layout_marginTop="25dp"/>

<Button
    android:id="@+id/btnSave"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_below="@+id/txtAddress"
    android:layout_marginTop="15dp"
    android:text="SAVE"/>
</LinearLayout>

Answer 1

试试这个，

    btnAdd.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View v) {
   // Start 2nd Activity

   if(selectedItem != 0){
            insertContact(name, email);
        }

        startActivity(new Intent(MainActivity.this, SecondActivity.class));
        finish()
    }
});

导航到Android中的其他活动时未找到任何活动

1 个答案: