.. _message-flashing-pattern:
Message Flashing
================
Good applications and user interfaces are all about feedback. If the user
does not get enough feedback he will probably end up hating the
application. Flask provides a really simple way to give feedback to a
user with the flashing system. The flashing system basically makes it
possible to record a message at the end of a request and access it next
request and only next request. This is usually combined with a layout
template that does this.
So here a full example::
from flask import flash, redirect, url_for, render_template
@app.route('/')
def index():
return render_template('index.html')
@app.route('/login', methods=['GET', 'POST'])
def login():
error = None
if request.method == 'POST':
if request.form['username'] != 'admin' or \
request.form['password'] != 'secret':
error = 'Invalid credentials'
else:
flash('You were sucessfully logged in')
return redirect(url_for('index'))
return render_template('login.html', error=error)
And here the ``layout.html`` template which does the magic:
.. sourcecode:: html+jinja
My Application
{% with messages = get_flashed_messages() %}
{% if messages %}
{% for message in messages %}
- {{ message }}
{% endfor %}
{% endif %}
{% endwith %}
{% block body %}{% endblock %}
And here the index.html template:
.. sourcecode:: html+jinja
{% extends "layout.html" %}
{% block body %}
Overview
Do you want to log in?
{% endblock %}
And of course the login template:
.. sourcecode:: html+jinja
{% extends "layout.html" %}
{% block body %}
Login
{% if error %}
Error: {{ error }}
{% endif %}
{% endblock %}