programming

How to pass data between screens in Flutter

In this article we will talk about three methods by which data can be passed from one screen to another in flutter. 1. Using constructors This is a very well known technique that is used in other languages as well. What we do is we pass the needed data in the constructor when we instatiate the target class. Lets assume that we have a screen say ConstructorScreen. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 class ConstructorScreen extends StatelessWidget { String message; ConstructorScreen(String m){ this.

How to authenticate and login users in Flutter from a REST Api

Introduction In this article we will discuss how to use a REST api backend to authenticate users from a Flutter app. We will build a very basic nodejs REST api backend. If you already have a backend then you can use that also. And then we will be building a basic Flutter app to connect to this backend and login to the app. It is assumed that the reader has a basic understanding of nodejs, rest api principles and flutter.

How to Use Textwatcher in Android

The Android framework provides the EditText interface element to allow the entry and editing of text. There are some use cases where one might need to detect text changes as they are typed in the EditText and react accordingly. One use case could be showing auto suggest values. The TextWatcher interface can be used for listening in for changes in text in an EditText. This interface has three abstract methods -  afterTextChanged(Editable s) beforeTextChanged(CharSequence s, int start, int count, int after) onTextChanged(CharSequence s, int start, int before, int count) Wiring the TextWatcher to the EditText If you take a look at EditText’s documentation, you won’t see any obvious way to wire the TextWatcher to it.

How to Use Datepicker in Flutter

Its not too tough, really. We are going to create a very simple project to demonstrate the use of the [datepicker] (https://api.flutter.dev/flutter/material/showDatePicker.html), in particular the material datepicker. Suggested readings Flutter for Beginners: An introductory guide to building cross-platform mobile applications with Flutter and Dart 2 Beginning App Development with Flutter: Create Cross-Platform Mobile Apps Lets see how its going to look. It just consists of a text and an icon button.

Writing A On Update Trigger in Postgresql

The previous [article] ( /posts/writing-a-on-delete-trigger-in-postgresql/) was about deletion trigger. This article is about update triggers. I had two tables what_did_you_eat and what_was_the_type. On insertion into what_did_you_eat, the what_type column was populated with the food type. Now, if I update the value in what column of a row from what_did_you_eat, I would want the corresponding row in what_was_the_type table to be updated too. For example, if we have the following data:

Writing a On Delete Trigger in Postgresql

The previous [article] ( /posts/writing-a-on-insert-trigger-in-postgresql/) was about insertion trigger. I had two tables what_did_you_eat and what_was_the_type. On insertion into what_did_you_eat, the what_type column was populated with the food type. Now, if I delete a row from what_did_you_eat, I would not want a row to remain in what_was_the_type to refer to a non existing row in the what_did_you_eat table. To handle this, I will use the delete trigger. Like before we first write the trigger function.

Writing A On Insert Trigger In Postgresql

Here is a simple example of a on insert postgresql trigger. I have a table called what_did_you_eat. It has the following structure - what will contain what was eaten. I have another table called what_was_the_type with the following structure - I want to store the type of food that was eaten in what_type column. And I want to do this to happen on insert into the what_did_you_eat table. So, off we go to write a trigger.

How To Parse Json In A Stored Procedure In Postgresql

Say we have a table called person with the following structure --------------------------- column| datatype --------------------------- _id | autonumber name | text age | integer --------------------------- We want to insert multiple records into the table using a stored procedure. If we have a stored procedure with say two input variables name and age, then it will take multiple calls. We can do this using a single call if we use a json input and using the json_to_recordset function.

Three Tier Architecture in Docker

In this article I am going to talk about how to do a classic 3-tier architecture using docker containers. The 3-tiers will be: Frontend tier: This will host the web application. Middle tier: This will host the api, in our case the REST api. Database tier: This will host the database. We want to expose the web application to the outside world. Simultaneously, we want this layer to be able to talk with the middle tier only not the database tier.

Upgrading Postgresql to V11

I run two instances of postgres servers - one on my local machine and the other one on my do virtual machine. Both of them are on debian. One of them was running 10.x and the other one 9.x version of postgres. I wanted to upgrade them to the latest version - that is version 11. I was pleasantly surprised to see how simple it was. This is what I did: