我們有時候在一個頁面存儲了一些信息，然后需要在另一個頁面使用，這個時候就需要使用flash，其實從應用需求角度來看session也能完成上面的需求，其實flash就是對session的封裝，它的底層實現其實也是session。
首先我們看下flash 和 get_flashed_message這兩個函數的源碼
def flash(message, category="message"):
"""Flashes a message to the next request. In order to remove the
flashed message from the session and to display it to the user,
the template has to call :func:`get_flashed_messages`.
.. versionchanged:: 0.3
`category` parameter added.
:param message: the message to be flashed.
:param category: the category for the message. The following values
are recommended: ``'message'`` for any kind of message,
``'error'`` for errors, ``'info'`` for information
messages and ``'warning'`` for warnings. However any
kind of string can be used as category.
"""
# Original implementation:
#
# session.setdefault('_flashes', []).append((category, message))
#
# This assumed that changes made to mutable structures in the session are
# always in sync with the session object, which is not true for session
# implementations that use external storage for keeping their keys/values.
flashes = session.get("_flashes", [])
flashes.append((category, message))
session["_flashes"] = flashes
message_flashed.send(
current_app._get_current_object(), message=message, category=category
)
def get_flashed_messages(with_categories=False, category_filter=()):
"""Pulls all flashed messages from the session and returns them.
Further calls in the same request to the function will return
the same messages. By default just the messages are returned,
but when `with_categories` is set to ``True``, the return value will
be a list of tuples in the form ``(category, message)`` instead.
Filter the flashed messages to one or more categories by providing those
categories in `category_filter`. This allows rendering categories in
separate html blocks. The `with_categories` and `category_filter`
arguments are distinct:
* `with_categories` controls whether categories are returned with message
text (``True`` gives a tuple, where ``False`` gives just the message text).
* `category_filter` filters the messages down to only those matching the
provided categories.
See :ref:`message-flashing-pattern` for examples.
.. versionchanged:: 0.3
`with_categories` parameter added.
.. versionchanged:: 0.9
`category_filter` parameter added.
:param with_categories: set to ``True`` to also receive categories.
:param category_filter: whitelist of categories to limit return values
"""
flashes = _request_ctx_stack.top.flashes
if flashes is None:
_request_ctx_stack.top.flashes = flashes = (
session.pop("_flashes") if "_flashes" in session else []
)
if category_filter:
flashes = list(filter(lambda f: f[0] in category_filter, flashes))
if not with_categories:
return [x[1] for x in flashes]
return flashes
從上面我可以再次認證flash就是利用session實現的。
下面講解下如何使用它。
1、首先也是先引入它
from flask imoport Flask,flash
2、在需要的地方寫入flash
@app.route('/login', methods=['GET', 'POST'])
def login():
error = None
if request.method == 'POST':
if request.form['username'] != app.config['USERNAME']:
error = 'Invalid username'
elif request.form['password'] != app.config['PASSWORD']:
error = 'Invalid password'
else:
session['logged_in'] = True
flash('You were logged in')
return redirect(url_for('index'))
return render_template('login.html', error=error)
3、在需要讀取的地方進行讀取
{% for message in get_flashed_messages() %}
<div class=flash>{{ message }}</div>
{% endfor %}
說明點：flash和它的名字一樣，是閃現，意思就是我們的消息只會顯示一次，當我們再次刷新也面的時候，它就不存在了，而正是這點，它經常被用來顯示一些提示消息，比如登陸之后，顯示歡迎信息等