1 // ========================================================================== 2 // Project: SproutCore - JavaScript Application Framework 3 // Copyright: ©2006-2011 Strobe Inc. and contributors. 4 // Portions ©2008-2011 Apple Inc. All rights reserved. 5 // License: Licensed under MIT license (see license.js) 6 // ========================================================================== 7 8 /** 9 @namespace 10 11 Support methods for the Delegate design pattern. 12 13 The Delegate design pattern makes it easy to delegate a portion of your 14 application logic to another object. This is most often used in views to 15 delegate various application-logic decisions to controllers in order to 16 avoid having to bake application-logic directly into the view itself. 17 18 The methods provided by this mixin make it easier to implement this pattern 19 but they are not required to support delegates. 20 21 ## The Pattern 22 23 The delegate design pattern typically means that you provide a property, 24 usually ending in "delegate", that can be set to another object in the 25 system. 26 27 When events occur or logic decisions need to be made that you would prefer 28 to delegate, you can call methods on the delegate if it is set. If the 29 delegate is not set, you should provide some default functionality instead. 30 31 Note that typically delegates are not observable, hence it is not necessary 32 to use get() to retrieve the value of the delegate. 33 34 @since SproutCore 1.0 35 36 */ 37 SC.DelegateSupport = { 38 39 /** 40 Selects the delegate that implements the specified method name. Pass one 41 or more delegates. The receiver is automatically included as a default. 42 43 This can be more efficient than using invokeDelegateMethod() which has 44 to marshall arguments into a delegate call. 45 46 @param {String} methodName 47 @param {Object...} delegate one or more delegate arguments 48 @returns {Object} delegate or null 49 */ 50 delegateFor: function(methodName) { 51 var idx = 1, 52 len = arguments.length, 53 ret ; 54 55 while(idx<len) { 56 ret = arguments[idx]; 57 if (ret && ret[methodName] !== undefined) return ret ; 58 idx++; 59 } 60 61 return (this[methodName] !== undefined) ? this : null; 62 }, 63 64 /** 65 Invokes the named method on the delegate that you pass. If no delegate 66 is defined or if the delegate does not implement the method, then a 67 method of the same name on the receiver will be called instead. 68 69 You can pass any arguments you want to pass onto the delegate after the 70 delegate and methodName. 71 72 @param {Object} delegate a delegate object. May be null. 73 @param {String} methodName a method name 74 @param {Object...} [args...] any additional arguments 75 76 @returns {Object} value returned by delegate 77 */ 78 invokeDelegateMethod: function(delegate, methodName) { 79 // Fast arguments access. 80 // Accessing `arguments.length` is just a Number and doesn't materialize the `arguments` object, which is costly. 81 var args = new Array(arguments.length - 2); // SC.A(arguments).slice(2) 82 for (var i = 0, len = args.length; i < len; i++) { args[i] = arguments[i + 2]; } 83 84 if (!delegate || !delegate[methodName]) delegate = this ; 85 86 var method = delegate[methodName]; 87 return method ? method.apply(delegate, args) : null; 88 }, 89 90 /** 91 Search the named delegates for the passed property. If one is found, 92 gets the property value and returns it. If none of the passed delegates 93 implement the property, search the receiver for the property as well. 94 95 @param {String} key the property to get. 96 @param {Object} delegate one or more delegate 97 @returns {Object} property value or undefined 98 */ 99 getDelegateProperty: function(key, delegate) { 100 var idx = 1, 101 len = arguments.length, 102 ret ; 103 104 while(idx<len) { 105 ret = arguments[idx++]; 106 if (ret && ret[key] != undefined) { 107 return ret.get ? ret.get(key) : ret[key] ; 108 } 109 } 110 111 return (this[key] != undefined) ? this.get(key) : undefined ; 112 } 113 114 }; 115