导航到Android中的其他活动时未找到任何活动

-4

btnAdd应该打开SecondActivity，收集新的电子邮件地址并将其返回到第一个活动并存储在数组中。然后它会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，它会一直追加到列表中，如果我从4个电子邮件地址开始，每次运行应用程序时，都会给它添加此错误。导航到Android中的其他活动时未找到任何活动

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", "[email protected]") >= 0){ 
     Toast.makeText(this, "Add successful.", Toast.LENGTH_SHORT).show(); 
    } 

    if (db.insertContact("John Smith", "[email protected]") >= 0) { 
     Toast.makeText(this, "Add successful.", Toast.LENGTH_SHORT).show(); 
    } 

    if (db.insertContact("Tom Brown", "[email protected]") >= 0){ 
     Toast.makeText(this, "Add successful.", Toast.LENGTH_SHORT).show(); 
    } 

    if (db.insertContact("Susie Brawn", "[email protected]") >= 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>

来源

2015-03-31 LizG

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() 
    } 
});

来源

2015-03-31 10:29:09

那是完美的。有效！！！我能问个问题吗？每次我进入应用程序时，它都会添加相同的数据并附加到数据库中。我怎样才能解决这个问题？ – LizG 2015-03-31 10:33:43

你是什么意思“我进入应用程序”？是你从第一个活动导航到第二个？ – 2015-03-31 10:36:54

当我从Android Studio运行应用程序时，需要将数据列出并添加到之前的内容中。如果您需要清空列表，则列表不会清除当我退出应用程序 – LizG 2015-03-31 10:39:39

导航到Android中的其他活动时未找到任何活动

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