在以下情况下,我在尝试解决延迟时遇到了一些问题
services.factory('MyService', ['$q',
function($q) {
var Foo = function() {
var deferred = $q.defer();
window.requestFileSystem = window.requestFileSystem || window.webkitRequestFileSystem;
window.requestFileSystem(window.TEMPORARY, 1024 * 1024, deferred.resolve, this.errorHandler);
return deferred.promise;
}
return {
Foo: Foo
}
}
]);
然后在控制器内:
var bar = new MyService.Foo().then(function(cb) {
console.log(cb)
});
如果我在requestFileSystem函数之外使用deferred.resolve,那么它可以很好地工作,但在上述情况下什么都不会发生。PS:requestFileSystem函数的第三个参数是一个回调,它在文件系统对象准备好后获取该对象。
编辑:这是条形码:
Object {then: function, catch: function, finally: function}
requestFileSystem的第四个参数是一个记录控制台文件系统API初始化错误的函数,但在这种情况下,由于requestFileSystem成功,因此不调用它,因此应调用deferred.resolve。如果我用正常函数替换deferred:
window.requestFileSystem(window.TEMPORARY, 1024 * 1024, function(filesystem){
console.log(filesystem);
}, this.errorHandler);
则正确返回文件系统对象:
DOMFileSystem {root: DirectoryEntry, name: "http_127.0.0.1_3000:Temporary"}
第2版:
我试着通过用自己的函数模拟requestFilesystem函数来进行一个简单的测试,它很有效:
var Foo = function() {
var deferred = $q.defer();
asd(deferred.resolve)
return deferred.promise;
}
function asd(callback) {
callback('it works')
}
MyService.Foo().then(function(cb){
console.log(cb)
})
基本问题是如何以及何时调用deferred.resolve
固定代码:
services.factory('MyService', ['$q','$rootScope',
function($q,$rootScope) {
var Foo = function() {
var deferred = $q.defer();
window.requestFileSystem = window.requestFileSystem || window.webkitRequestFileSystem;
window.requestFileSystem(window.TEMPORARY, 1024 * 1024, function(result){
deferred.resolve(result);
$rootScope.$apply();//force angular to resolve promise
}, this.errorHandler);
return deferred.promise;
}
return {
Foo: Foo
}
}
]);
问题是,当您在angular生命周期之外调用"deferred.resolve"(文件系统请求的回调在angular寿命周期之外)时,您必须手动调用"$rootScope"$apply()',否则承诺将不会得到解决。
github.com/maciel310/angular-filesystem 提供了更好的解决方案
//wrap resolve/reject in an empty $timeout so it happens within the Angular call stack
//easier than .apply() since no scope is needed and doesn't error if already within an apply
function safeResolve(deferral, message) {
$timeout(function() {
deferral.resolve(message);
});
}
function safeReject(deferral, message) {
$timeout(function() {
deferral.reject(message);
});
}