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AngularJS数据绑定中数据监控的机制说明
from : http://docs.angularjs.org/guide/scope
When the browser calls into JavaScript the code executes outside the Angular execution context, which means that Angular is unaware of model modifications. To properly process model modifications the execution has to enter the Angular execution context using the $apply
method. Only model modifications which execute inside the $apply
method will be properly accounted for by Angular. For example if a directive listens on DOM events, such as ng-click
it must evaluate the expression inside the $apply
method.
After evaluating the expression, the $apply
method performs a $digest
. In the $digest phase the scope examines all of the $watch
expressions and compares them with the previous value. This dirty checking is done asynchronously. This means that assignment such as $scope.username="angular"
will not immediately cause a $watch
to be notified, instead the $watch
notification is delayed until the $digest
phase. This delay is desirable, since it coalesces multiple model updates into one $watch
notification as well as it guarantees that during the $watch
notification no other $watch
es are running. If a $watch
changes the value of the model, it will force additional $digest
cycle.
AngularJS数据绑定中数据监控的机制说明