| 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 %} |
|
|
