Question

当数据库中没有数据存储时，我想显示一个alertDialog。但是我所尝试的似乎没有达到预期目标，因为当数据库为空时不会调用警告对话框。

以下是我检查数据库中表格存在的方法：

public boolean checkForTables() {
        boolean hasTables = false;
        SQLiteDatabase db = this.getWritableDatabase();
        Cursor cursor = db.rawQuery("SELECT COUNT(*)FROM" + CONTACTS_TABLE_NAME, null);
        if (cursor != null && cursor.getCount() > 0) {
            hasTables = true;
            cursor.close();
        }
        return hasTables;
    }

在我的创作活动中：

if (myDb.checkForTables()) {
            showTable();
            btn.setVisibility(View.VISIBLE);
        } else {
            showAlert();
            btn.setVisibility(View.GONE);
        }

方法 showTable（）

private void showTable() {
        ArrayList<String> array_list = myDb.getAllContacts();

        ArrayAdapter arrayAdapter;
        arrayAdapter = new ArrayAdapter(this, android.R.layout.simple_list_item_1, array_list);

        //adding it to the list view.
        obj = (ListView) findViewById(R.id.listView1);
        obj.setAdapter(arrayAdapter);
    }

方法 showAlert（）

public void showAlert() {
        LayoutInflater inflater = (LayoutInflater) this.getSystemService(LAYOUT_INFLATER_SERVICE);
        View layout = inflater.inflate(R.layout.empty_basket, (ViewGroup) findViewById(R.id.root));
        AlertDialog.Builder adb = new AlertDialog.Builder(this);
        adb.setView(layout);
        adb.setCancelable(false);

        adb.setPositiveButton("Add items to basket", new DialogInterface.OnClickListener() {
            public void onClick(DialogInterface dialog, int which) {
                Intent i = new Intent(MyBasket.this, MainActivity.class);
                startActivity(i);
            }
        });
        adb.show();
    }

我的活动完整代码：

public class MyBasket extends ActionBarActivity {
    private ListView obj;
    DBHelper myDb;
    int numRows;
    int id_To_Update = 0;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_my_basket);
        Toolbar toolbar = (Toolbar) findViewById(R.id.app_bar);
        setSupportActionBar(toolbar);

        getSupportActionBar().setHomeButtonEnabled(true);
        getSupportActionBar().setDisplayHomeAsUpEnabled(true);
        myDb = new DBHelper(this);
        Button btn = (Button) findViewById(R.id.checkout);
        if (myDb.checkForTables()) {
            showTable();
            btn.setVisibility(View.VISIBLE);
        } else {
            showAlert();
            btn.setVisibility(View.GONE);
        }

        TextView txt = (TextView) findViewById(R.id.numRows);
        myDb.numberOfRows();
        txt.setText(Integer.toString(numRows));


        Button basketButton = (Button) findViewById(R.id.checkout);
        basketButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                AlertDialog.Builder alertDialog = new AlertDialog.Builder(MyBasket.this);
                alertDialog.setCancelable(false);
                alertDialog.setMessage("Done with shopping?");
                alertDialog.setPositiveButton("Proceed to checkout", new DialogInterface.OnClickListener() {
                    public void onClick(DialogInterface dialog, int which) {
                        Intent intent = new Intent(MyBasket.this, CheckOut.class);
                        startActivity(intent);
                    }
                });

                alertDialog.setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
                    public void onClick(DialogInterface dialog, int which) {
                        dialog.cancel();
                    }
                });
                alertDialog.show();
            }
        });
    }

    public void showAlert() {
        LayoutInflater inflater = (LayoutInflater) this.getSystemService(LAYOUT_INFLATER_SERVICE);
        View layout = inflater.inflate(R.layout.empty_basket, (ViewGroup) findViewById(R.id.root));
        AlertDialog.Builder adb = new AlertDialog.Builder(this);
        adb.setView(layout);
        adb.setCancelable(false);

        adb.setPositiveButton("Add items to basket", new DialogInterface.OnClickListener() {
            public void onClick(DialogInterface dialog, int which) {
                Intent i = new Intent(MyBasket.this, MainActivity.class);
                startActivity(i);
            }
        });
        adb.show();
    }

    private void showTable() {
        ArrayList<String> array_list = myDb.getAllContacts();

        ArrayAdapter arrayAdapter;
        arrayAdapter = new ArrayAdapter(this, android.R.layout.simple_list_item_1, array_list);

        //adding it to the list view.
        obj = (ListView) findViewById(R.id.listView1);
        obj.setAdapter(arrayAdapter);
    }


    @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_my_basket, 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;
        }
        if (id == R.id.action_delete) {
            myDb.deleteContact();
            Toast.makeText(getApplicationContext(), "Deleted Successfully", Toast.LENGTH_SHORT).show();
            Intent intent = new Intent(MyBasket.this, MyBasket.class);
            startActivity(intent);
            return true;

        }
        if (id == android.R.id.home) {
            NavUtils.navigateUpFromSameTask(this);
        }
        return super.onOptionsItemSelected(item);
    }

    public boolean onKeyDown(int keycode, KeyEvent event) {
        if (keycode == KeyEvent.KEYCODE_BACK) {
            moveTaskToBack(true);
        }
        return super.onKeyDown(keycode, event);
    }
}

任何帮助将不胜感激。谢谢。

Answer 1

＆＃39; SELECT COUNT（*）...`将返回一个游标和一个值。您需要检查返回的值以确定表是否为空，而不是查看游标结果集的大小：

public boolean checkForTables() {
    boolean hasTables = false;
    SQLiteDatabase db = this.getWritableDatabase();
    Cursor cursor = db.rawQuery("SELECT COUNT(*)FROM" + CONTACTS_TABLE_NAME, null);
    if (cursor != null) {
        if( cursor.moveToFirst() ) {
            if( cursor.getInt(0) > 0 ) {
                hasTables = true;
            }
        cursor.close();
    }
    return hasTables;
}

Answer 2

问题在于您选择的是计数而不是行，所以每次显示计数时都会有一行，即使是零。

public boolean checkForTables() {
    boolean hasRows = false;
    SQLiteDatabase db = getReadableDatabase();
    Cursor cursor = db.rawQuery("SELECT COUNT(*) FROM " + TABLE_COMMENTS, null);
    cursor.moveToFirst();
    int count = cursor.getInt(0);
    if(count > 0)
        hasRows = true;
    db.close();
    return hasRows;
}

在解决了没有显示对话框的问题之后，代码中还有另一个问题，你会得到IllegalStateException因为这个问题;）

View layout = inflater.inflate(R.layout.empty_basket, (ViewGroup) findViewById(R.id.root));

您应该将null作为父视图传递，因为它将进入对话框布局

View layout = inflater.inflate(R.layout.empty_basket, null);

当sqlite数据库为空时，如何在活动中显示alertDialog

2 个答案: