| | Message Flashing |
| | ================ |
| |
|
| | Good applications and user interfaces are all about feedback. If the user |
| | does not get enough feedback they 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. Note that browsers and sometimes web servers enforce |
| | a limit on cookie sizes. This means that flashing messages that are too |
| | large for session cookies causes message flashing to fail silently. |
| |
|
| | Simple Flashing |
| | --------------- |
| |
|
| | So here is a full example:: |
| |
|
| | from flask import Flask, flash, redirect, render_template, \ |
| | request, url_for |
| |
|
| | app = Flask(__name__) |
| | app.secret_key = b'_5#y2L"F4Q8z\n\xec]/' |
| |
|
| | @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 successfully logged in') |
| | return redirect(url_for('index')) |
| | return render_template('login.html', error=error) |
| |
|
| | And here is the :file:`layout.html` template which does the magic: |
| |
|
| | .. sourcecode:: html+jinja |
| |
|
| | <!doctype html> |
| | <title>My Application</title> |
| | {% with messages = get_flashed_messages() %} |
| | {% if messages %} |
| | <ul class=flashes> |
| | {% for message in messages %} |
| | <li>{{ message }}</li> |
| | {% endfor %} |
| | </ul> |
| | {% endif %} |
| | {% endwith %} |
| | {% block body %}{% endblock %} |
| |
|
| | Here is the :file:`index.html` template which inherits from :file:`layout.html`: |
| |
|
| | .. sourcecode:: html+jinja |
| |
|
| | {% extends "layout.html" %} |
| | {% block body %} |
| | <h1>Overview</h1> |
| | <p>Do you want to <a href="{{ url_for('login') }}">log in?</a> |
| | {% endblock %} |
| |
|
| | And here is the :file:`login.html` template which also inherits from |
| | :file:`layout.html`: |
| |
|
| | .. sourcecode:: html+jinja |
| |
|
| | {% extends "layout.html" %} |
| | {% block body %} |
| | <h1>Login</h1> |
| | {% if error %} |
| | <p class=error><strong>Error:</strong> {{ error }} |
| | {% endif %} |
| | <form method=post> |
| | <dl> |
| | <dt>Username: |
| | <dd><input type=text name=username value= |
| | request.form.username }} |
| | <dt>Password: |
| | <dd><input type=password name=password> |
| | </dl> |
| | <p><input type=submit value=Login> |
| | </form> |
| | {% endblock %} |
| |
|
| | Flashing With Categories |
| | ------------------------ |
| |
|
| | .. versionadded:: 0.3 |
| |
|
| | It is also possible to provide categories when flashing a message. The |
| | default category if nothing is provided is ``'message'``. Alternative |
| | categories can be used to give the user better feedback. For example |
| | error messages could be displayed with a red background. |
| |
|
| | To flash a message with a different category, just use the second argument |
| | to the :func:`~flask.flash` function:: |
| |
|
| | flash('Invalid password provided', 'error') |
| |
|
| | Inside the template you then have to tell the |
| | :func:`~flask.get_flashed_messages` function to also return the |
| | categories. The loop looks slightly different in that situation then: |
| |
|
| | .. sourcecode:: html+jinja |
| |
|
| | {% with messages = get_flashed_messages(with_categories=true) %} |
| | {% if messages %} |
| | <ul class=flashes> |
| | {% for category, message in messages %} |
| | <li class="{{ category }}">{{ message }}</li> |
| | {% endfor %} |
| | </ul> |
| | {% endif %} |
| | {% endwith %} |
| |
|
| | This is just one example of how to render these flashed messages. One |
| | might also use the category to add a prefix such as |
| | ``<strong>Error:</strong>`` to the message. |
| |
|
| | Filtering Flash Messages |
| | ------------------------ |
| |
|
| | .. versionadded:: 0.9 |
| |
|
| | Optionally you can pass a list of categories which filters the results of |
| | :func:`~flask.get_flashed_messages`. This is useful if you wish to |
| | render each category in a separate block. |
| |
|
| | .. sourcecode:: html+jinja |
| |
|
| | {% with errors = get_flashed_messages(category_filter=["error"]) %} |
| | {% if errors %} |
| | <div class="alert-message block-message error"> |
| | <a class="close" href="#">×</a> |
| | <ul> |
| | {%- for msg in errors %} |
| | <li>{{ msg }}</li> |
| | {% endfor -%} |
| | </ul> |
| | </div> |
| | {% endif %} |
| | {% endwith %} |
| |
|
