Question

在命令式C ++中，我可以使用for(my.list in c("a", "b")) { assign(my.list, `names<-`(get(my.list), c("element1", "element2"))) } a #$element1 #[1] 1 #$element2 #[1] 2 b #$element1 #[1] 3 #$element2 #[1] 4来连续询问用户几个问题。根据用户的答案（“是”，“否”，“确定”，“中止”），我可以继续前进。

但是在QML中，由于其声明性，它似乎是一项艰巨的任务。仍然可以创建一堆对话框，但依赖于答案的状态（信息）应该存储在QDialog / onAccepted / ...事件之间。如果与C ++代码（模型/单例）有很多交互，那就特别难了。

是否有任何一般的方法/技巧/习惯用法只使用一系列模态弹出窗口轻松创建类似“安装程序”的东西？

Answer 1

首先，和其他人之前提到的一样，对于更长的事件链，你真的需要使用类似状态机的东西。

话虽如此，在实践中，与对话相关的大多数事情涉及最多2-3个级别的问题。回调非常适合：

你正在寻找的基本Api是：

g_dialogs.confirm({
                     title: 'Discard unsaved changes?',
                     message: 'You have unsaved changes here.\n' +
                              'Are you sure you want to open a new file?'
                  },
                  function(result){
                    if(result) {
                      g_dialogs.fileDialog({title: 'Select an Image'},
                                           function(fileUrl){
                                             loadFile(fileUrl)
                                           })
                    }
                 })

其中g_dialogs指向Dialogs项的全局实例。您甚至可以使用QML单例。

<强> Dialogs.qml ：

import QtQuick 2.0
import QtQuick.Dialogs 1.2

Item
{
    property var dialogs: []
    property var callbacks: []

    /**
     * Creates a modal dialog pointed by the dialogSource qml file.
     * For this functioanlity to work, the dialogSource MUST be an instance of Dialog component
     * properties are the objects that will be passed on to the dialogSource' component
     * property must not contain a key called 'dialogId'
     * callback is the callback function that will be called with the result,
     * once the user finishes interacting with the dialog. (eg. confirms/dismisses and event)
     **/
    function showDialog(dialogSource, properties, callback) {
        if (properties === undefined)
            properties = {}

        if (properties['dialogId']) {
            console.error('You cannot use the property name dialogId')
            return -1
        }

        properties["dialogId"] = dialogs.length

        var dialog
        var component = Qt.createComponent(dialogSource)
        var result = -1

        if (component.status === Component.Ready) {
            dialog = component.createObject(parent, properties)
            callbacks.push(callback)
            dialogs.push(dialog)
            result = dialogs.length - 1
        }
        else {
            console.error(component.errorString())
        }

        return result
    }

    /**
     * Internal function used by Dialog
     * to return the result to the original caller via. the callback
     */
    function returnDialog(index, result) {
        if (index < 0 || index >= callbacks.length)
            return

        var callback = callbacks[index]
        var dialog = dialogs[index]

        callbacks.splice(index, 1)
        dialogs.splice(index, 1)

        if (dialog !== undefined)
           dialog.destroy()

        if (callback !== undefined)
            callback(result)
    }

    /**
     * Convenience method to create a confirmation dialog where the user is presented with a yes/no question
     * Asks the user whether he wants to confirm/reject an action.
     * properties can be an Object of {title: 'Window title', text: 'Text', icon: ''}
     * Once the user finishes interacting with dialog, the callback will be called with the result
     */
    function confirm(properties, callback) {
        properties["title"] = properties["title"]
                              ? properties["title"]
                              : qsTr("Warning")
        properties["text"] =  properties["text"]
                              ? properties["text"]
                              : qsTr("Are you sure?")

        properties["standardButtons"] = StandardButton.Yes | StandardButton.No

        return showDialog("MessageDialog.qml", properties, callback)
    }

    // Convenience wrapper around FileDialog.qml
    function fileDialog(properties, callback) {
        return showDialog("FileDialog.qml", properties, callback)
    }

}

其中，每个对话框都是 Dialog.qml 的实例：

import QtQuick 2.0

Item
{
    id: modalDialog

    readonly property int dialogId: 0

    signal done(var result)

    onDone: g_dialogs.returnDialog(dialogId, result)
}

例如。的 MessageDialog.qml ：

import QtQuick 2.0 import QtQuick.Controls 1.2 import QtQuick.Dialogs 1.2 import '.' Dialog { property alias title: dialog.title property alias text: dialog.text property alias icon: dialog.icon property alias standardButtons: dialog.standardButtons MessageDialog { id: dialog modality: Qt.ApplicationModal standardButtons: StandardButton.Yes | StandardButton.No icon: StandardIcon.Warning onAccepted: done(true) onYes: done(true) onNo: done(false) onDiscard: done(false) onRejected: done(false) } //Variables in other windows don't seem to reflect the property changes in here. //So show the window only after all the properties are set. Component.onCompleted: dialog.visible = true }

例如。的 FileDialog.qml ：

import QtQuick 2.0 import QtQuick.Controls 1.2 import QtQuick.Dialogs 1.2 import '.' Dialog { property alias title: dialog.title property alias fileUrl: dialog.fileUrl property alias fileUrls: dialog.fileUrls property alias folder: dialog.folder property alias modality: dialog.modality property alias nameFilters: dialog.nameFilters property alias selectExisting: dialog.selectExisting property alias selectFolder: dialog.selectFolder property alias selectMultiple: dialog.selectMultiple property alias selectedNameFilter: dialog.selectedNameFilter property alias shortcuts: dialog.shortcuts property alias sidebarVisible: dialog.sidebarVisible FileDialog { id: dialog onAccepted: { if (selectMultiple) done(fileUrls) else done(fileUrl) } onRejected: done(null) } Component.onCompleted: dialog.visible = true }

P.S关于这个api的好处是这些回调函数是很好的Javascript闭包，因此在ListView / Repeater委托中使用这种方法时，你不必传递讨厌的引用。

一系列模态对话框

1 个答案: