android - 在 Toast 中显示电话号码

Question

好的，我几乎所有东西都在工作。唯一的问题是，每当我单击通过对话框添加到列表视图中的新条目时，应用程序就会崩溃，而不是在 toast 中显示电话号码。我想要它做的如下（大多数步骤都正常工作）

我通过模拟器上的菜单按钮进入对话框，然后单击对话框的菜单项。
我输入姓名和电话号码（我用我的作为测试）
它将数据作为联系人对象传递给 ArrayAdapter，ArrayAdapter 将添加到 MainActivity 中的 ListView。
当我单击新条目时，它会获取联系人的姓名，然后在数据库中查找与该姓名关联的电话号码并将其显示在 toast 中。（该部分无法正常工作，导致上述崩溃）

AddContactFragment.java：

    package com.example.java2lab10_lefelhocz;

    import com.example.java2lab10_lefelhocz.R;

    import android.app.AlertDialog;
    import android.app.Dialog;
    import android.app.DialogFragment;
    import android.content.DialogInterface;
    import android.content.DialogInterface.OnClickListener;
    import android.os.Bundle;
    import android.view.LayoutInflater;
    import android.widget.*;

    public class AddContactFragment extends DialogFragment 
    {

    private EditText txtNameEdit;
    private EditText txtPhoneEdit;


    private LayoutInflater inflater;

    // called when the DialogFragment is created
    public Dialog onCreateDialog(Bundle savedInstanceState)
    {
    // create the dialog builder
    AlertDialog.Builder builder = new AlertDialog.Builder(getActivity());     

    // Get the layout inflater object    
    inflater = getActivity().getLayoutInflater();      

    // Inflate and set the layout for the dialog     
    // Pass null as the parent view because its going in the dialog layout     
    builder.setView(inflater.inflate(R.layout.add_contact, null));
    builder.setTitle("Add a Contact");


    builder.setPositiveButton("Add", new OnClickListener(){

    @Override
    public void onClick(DialogInterface dialog, int which) {
        // TODO Auto-generated method stub
        txtNameEdit = (EditText)getDialog().findViewById(R.id.txtNameEdit);
        txtPhoneEdit =      (EditText)getDialog().findViewById(R.id.txtPhoneEdit);
        MainActivity ma = (MainActivity)getActivity();
        ma.addContact(txtNameEdit.getText().toString(),     txtPhoneEdit.getText().toString());

    }

    });



    builder.setNegativeButton("Cancel", new OnClickListener(){

    @Override
    public void onClick(DialogInterface dialog, int which) {
        // TODO Auto-generated method stub
        dialog.dismiss();
    }

    });
    return builder.create();
     }
    }

联系方式.java：

       // Project:          Java2Lab10_Lefelhocz
       // File:         Contact.java
    // Date:            11/1/12
    // Description:     This class represents a contact

    package com.example.java2lab10_lefelhocz;  

    public class Contact 
    { 

        //private variables 
        private int _id; 
        private String _name; 
        private String _phone_number; 

        // Empty constructor 
        public Contact()
        { 

        } 
        // constructor 
         public Contact(int id, String name, String _phone_number)
        { 
         this._id = id; 
         this._name = name; 
         this._phone_number = _phone_number; 
         } 

         // constructor 
         public Contact(String name, String _phone_number)
         { 
         this._name = name; 
         this._phone_number = _phone_number; 
         } 
         // getting ID 
         public int getID()
         { 
         return this._id; 
         } 

        // setting id 
        public void setID(int id)
        { 
             this._id = id; 
        } 

        // getting name 
        public String getName()
        { 
            return this._name; 
        } 

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

      // getting phone number 
      public String getPhoneNumber()
      { 
    return this._phone_number; 
      } 

      // setting phone number 
      public void setPhoneNumber(String phone_number)
      { 
           this._phone_number = phone_number; 
       } 
         public String toString(){
     return _name;
         }
         }

数据库处理程序.java

     // Project:            Java2Lab10_Lefelhocz
     // File:           DatabaseHandler.java
     // Date:           04/3/13
     // Description:        This class handles all database operations
     //                 Databases opened for write should be      closed.

    package com.example.java2lab10_lefelhocz;

    import java.util.ArrayList;
    import java.util.List;

    import com.example.java2lab10_lefelhocz.Contact;

    import android.content.ContentValues;
    import android.content.Context;
    import android.database.Cursor;
    import android.database.sqlite.SQLiteDatabase;
    import android.database.sqlite.SQLiteOpenHelper;

    // This class extends SQLiteOpenHelper and handles all database operations
    public class DatabaseHandler extends SQLiteOpenHelper 
    {
// All Static variables 
    // Database Version 
    private static final int DATABASE_VERSION = 1; 

    // Database Name 
    private static final String DATABASE_NAME = "contactsManager"; 

    // Contacts table name 
    private static final String TABLE_CONTACTS = "contacts"; 

    // Contacts Table Columns names 
    private static final String KEY_ID = "id"; 
    private static final String KEY_NAME = "name"; 
    private static final String KEY_PH_NO = "phone_number"; 

    // constructor
    public DatabaseHandler(Context context) 
    { 
    super(context, DATABASE_NAME, null, DATABASE_VERSION); 
    } 

    // Creating Tables 
    // Called when the database is created for the first time. 
    // This is where the creation of tables and the initial population of the tables         should happen.
    @Override
    public void onCreate(SQLiteDatabase db) 
    { 
    // SQLite Create syntax 
    //CREATE TABLE NameOfTable(Column1 Type, Column2 Type);

    String CREATE_CONTACTS_TABLE = "CREATE TABLE " + TABLE_CONTACTS + "("
            + KEY_ID + " INTEGER PRIMARY KEY," + KEY_NAME + " TEXT,"
            + KEY_PH_NO + " TEXT" + ")"; 
    //                + KEY_PH_NO + " TEXT," + " UNIQUE (" + KEY_NAME + "))";
    db.execSQL(CREATE_CONTACTS_TABLE); 
    } 

    // Upgrading database 
    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) 
    { 
    // Drop older table if existed 
    db.execSQL("DROP TABLE IF EXISTS " + TABLE_CONTACTS); 

    // Create tables again 
    onCreate(db); 
    }

   // adds a new contact 
   public void addContact(Contact contact) 
   { 
    // get the database from the SQLiteHelper
    SQLiteDatabase db = this.getWritableDatabase(); 

    // This class is used to store a set of key/values that the ContentResolver can process. 
    ContentValues values = new ContentValues(); 
    values.put(KEY_NAME, contact.getName()); // Contact Name 
    values.put(KEY_PH_NO, contact.getPhoneNumber()); // Contact Phone Number 

    // Inserting Row 
    // SQLite Syntax 
    // INSERT INTO TableName(ColumnValue, ColumnValue)
    db.insert(TABLE_CONTACTS, null, values); 
    db.close(); // Closing database connection
    }

    // retrieve single contact by id
    public Contact getContact(int id) 
    { 
    // get the database from the SQLiteHelper
    SQLiteDatabase db = this.getReadableDatabase(); 

    // query the table and return a Cursor
    // SQLite Syntax
    // SELECT * FROM TableName WHERE Column=Value;
    Cursor cursor = db.query(TABLE_CONTACTS, new String[] { KEY_ID, 
            KEY_NAME, KEY_PH_NO }, KEY_ID + "=?", 
            new String[] { String.valueOf(id) }, null, null, null, null); 
    if (cursor != null) 
        cursor.moveToFirst(); 

    // Create a Contact object from the Cursor
    Contact contact = new Contact(Integer.parseInt(cursor.getString(0)), 
            cursor.getString(1), cursor.getString(2)); 

    // close the cursor
    cursor.close();

    // close the database
    db.close();

    // return contact 
    return contact; 
    } 

    public Contact getContact(String name) 
    { 
    // get the database from the SQLiteHelper
    SQLiteDatabase db = this.getReadableDatabase(); 

    // query the table and return a Cursor
    // SQLite Syntax
    // SELECT * FROM TableName WHERE Column=Value;
    Cursor cursor = db.query(TABLE_CONTACTS, new String[] { KEY_ID, 
            KEY_NAME, KEY_PH_NO }, KEY_NAME + "=?", 
            new String[] { name }, null, null, null, null); 
    if (cursor != null) 
        cursor.moveToFirst(); 

    // Create a Contact object from the Cursor
    Contact contact = new Contact(Integer.parseInt(cursor.getString(0)), 
            cursor.getString(1), cursor.getString(2)); 

    // close the cursor
    cursor.close();

    // close the database
    db.close();

    // return contact 
    return contact; 
    } 
    // return a List of All Contacts in table
    public List<Contact> getAllContacts() 
    { 
    List<Contact> contactList = new ArrayList<Contact>(); 
    // Select All Query 
    String selectQuery = "SELECT  * FROM " + TABLE_CONTACTS; 

    //       SQLiteDatabase db = this.getWritableDatabase(); 
    SQLiteDatabase db = this.getReadableDatabase();

    // execute a raw SQLite query
    Cursor cursor = db.rawQuery(selectQuery, null); 

    // looping through all rows and adding to list 
    if (cursor.moveToFirst()) 
    { 
       do 
       { 
           // create a new Contact object
           Contact contact = new Contact(); 
           // get the data from the cursor and assign it to the contact
           contact.setID(Integer.parseInt(cursor.getString(0))); 
           contact.setName(cursor.getString(1)); 
           contact.setPhoneNumber(cursor.getString(2)); 
           // Adding contact to list 
           contactList.add(contact); 
       } while (cursor.moveToNext()); 
    } 

    // close the cursor
    cursor.close();

    // return contact list 
    return contactList; 
    } 

    // return Count of all Contacts in table 
    public int getContactsCount() 
    { 
    String countQuery = "SELECT  * FROM " + TABLE_CONTACTS; 
    SQLiteDatabase db = this.getReadableDatabase(); 
    Cursor cursor = db.rawQuery(countQuery, null);  

    // return count 
    return cursor.getCount(); 
    }

    // Updating single contact 
    public int updateContact(Contact contact) 
    { 
    SQLiteDatabase db = this.getWritableDatabase(); 

    // This class is used to store a set of key/values that the ContentResolver can process. 
    ContentValues values = new ContentValues(); 
    values.put(KEY_NAME, contact.getName()); 
    values.put(KEY_PH_NO, contact.getPhoneNumber()); 

    // updating row 
    int n = db.update(TABLE_CONTACTS, values, KEY_ID + " = ?", 
            new String[] { String.valueOf(contact.getID()) }); 
    db.close();
    return n;

    } 

    // Deleting single contact 
    public void deleteContact(Contact contact) 
    { 
    SQLiteDatabase db = this.getWritableDatabase(); 
    db.delete(TABLE_CONTACTS, KEY_ID + " = ?", 
            new String[] { String.valueOf(contact.getID()) });  
    db.close(); // Closing database connection
    }

    // delete all the Contacts
    public void deleteAllContacts()
    {
    SQLiteDatabase db = this.getWritableDatabase();
    db.delete(TABLE_CONTACTS, null, null);
    db.close(); // Closing database connection
    }

    // returns a cursor with all the Contacts
    public Cursor getAllCursor() 
    { 
    // Select All Query 
    String selectQuery = "SELECT  * FROM " + TABLE_CONTACTS; 

    SQLiteDatabase db = this.getReadableDatabase();

    // execute a raw SQLite query
    Cursor cursor = db.rawQuery(selectQuery, null); 

    // return the Cursor
    return cursor; 
    } 
    }

MainActivity.java：

    // Project:         Java2Lab10_Lefelhocz
    // File:            MainActivity.java
    // Date:            04/3/13
    // Description:     This class is the main activity for the application
    //                  Its purpose is to demonstrate the SQLiteHelper and to test
    //                  adding, deleting, updating and listing entries in   the database.

    package com.example.java2lab10_lefelhocz;


    import java.util.List;




    import android.os.Bundle;
    import android.app.Activity;
    import android.app.DialogFragment;
    import android.content.Context;
    import android.view.Menu;
    import android.view.MenuItem;
    import android.view.View;
    import android.widget.AdapterView;
    import android.widget.ArrayAdapter;
    import android.widget.ListView;
    import android.widget.TextView;
    import android.widget.Toast;

    public class MainActivity extends Activity implements  AdapterView.OnItemClickListener
    {
private DatabaseHandler dbh;
private ListView contactsListView ;
private ArrayAdapter<Contact> adapter ;
@Override
protected void onCreate(Bundle savedInstanceState) 
{
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    contactsListView = (ListView) findViewById( R.id.contactsListView );


    dbh = new DatabaseHandler(this); 

    // delete all entries in Contacts table
    dbh.deleteAllContacts();
    // set the Activity to listen for the onItemClick event
    contactsListView.setOnItemClickListener(this);

    // create the ArrayAdapter
    adapter = createAdapter();

    // Set the ArrayAdapter as the ListView's adapter.
    contactsListView.setAdapter( adapter );

    // create the database handler object




}

protected ArrayAdapter<Contact> createAdapter() {
    // TODO Auto-generated method stub
    List<Contact> contacts = dbh.getAllContacts();
    ArrayAdapter<Contact> contactsAdapter = new ArrayAdapter<Contact> (this,android.R.layout.simple_list_item_1, contacts);

    return contactsAdapter;
}

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

// this method displays the current list of Contacts
    public void displayContacts()
    {
    // create a list of Contacts
    List<Contact> contacts = dbh.getAllContacts();

    // create the string builder message
    StringBuilder message = new StringBuilder();

    // display headings
    message.append("Total: " + dbh.getContactsCount() + "\n");
    message.append(String.format("%-5s%-10s%-10s\n", "Id:", "Name:", "Phone:"));

    // Use list of contacts to build a StringBuffer that will be displayed in the   TextView
    for(Contact cn : contacts)
    {
        message.append(String.format("%-5s%-10s%-10s\n", cn.getID(), cn.getName(),         cn.getPhoneNumber()));
    }

    // display the StringBuilder with all the contacts

    }

    public boolean onOptionsItemSelected(MenuItem item) {
    // Handle item selection
    switch (item.getItemId()) {
    case R.id.menu_add_contact:
        DialogFragment myFragment = new AddContactFragment();
        myFragment.show(getFragmentManager(), "customDialog");

    default:
        return super.onOptionsItemSelected(item);
    }
    }
    public void addContact(String newName, String newPhone)
    {
    Contact c = new Contact(newName, newPhone);
    dbh.addContact(c);
     adapter.add(c);
    }

@Override
public void onItemClick(AdapterView<?> arg0, View view, int arg2, long arg3) {
    Context context = null;

    // TODO Auto-generated method stub
    Contact c1 = dbh.getContact(((TextView)view).getText().toString());
    Toast.makeText(context, "Phone Number: " + c1.getPhoneNumber(), Toast.LENGTH_LONG).show();
}


    }

score 2 · Accepted Answer

在这里：

Context context = null; //<<<<

context在将其传递给Toast.makeText方法之前，您忘记使用当前 Activity 上下文进行初始化。将其初始化为：

Context context = MainActivity.this;

score 0 · Accepted Answer

看起来您正在调用上下文makeToast。nullAndroid 文档说：

Context context = getApplicationContext();
CharSequence text = "Hello toast!";
int duration = Toast.LENGTH_SHORT;

Toast toast = Toast.makeText(context, text, duration);
toast.show();

score 0 · Accepted Answer

Toast.makeText(context, "Phone Number: " + c1.getPhoneNumber(), Toast.LENGTH_LONG).show();

在这一行中，只需替换contextwith即可getApplicationContext()。问题是由于上下文被初始化为null.

android - 在 Toast 中显示电话号码

3 回答 3

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