如何使用Ubuntu SDK中的Download Manager来下载文件

对于一下应用来说，我们需要使用网路上的一下文件，并下载它们。那么我们怎么在QML应用中来下载文件呢？我们在SDK API的网页中，我们发现有一个叫做Download Manager的API。我们可以使用SingleDownload或DownloadManager来下载一个或多个文件。

首先，我们来创建一个简单的Download应用。这里我们使用“QML app with Simple UI (qmlproject)”。对于大家不熟悉Download Manager的开发者来说，我们可以使用如下的方法得到它更加详细的接口：

$qmlplugindump Ubuntu.DownloadManager 0.1

通过上面的命令，我们可以得到如下的输出：

import QtQuick.tooling 1.1// This file describes the plugin-supplied types contained in the library.// It is used for QML tooling purposes only.//// This file was auto-generated by:// 'qmlplugindump Ubuntu.DownloadManager 0.1'Module {    Component {        name: "Ubuntu::DownloadManager::DownloadError"        prototype: "QObject"        exports: ["Error 0.1"]        exportMetaObjectRevisions: [0]        Property { name: "type"; type: "string"; isReadonly: true }        Property { name: "message"; type: "string"; isReadonly: true }    }    Component {        name: "Ubuntu::DownloadManager::Metadata"        prototype: "QObject"        exports: ["Metadata 0.1"]        exportMetaObjectRevisions: [0]        Property { name: "title"; type: "string" }        Property { name: "showInIndicator"; type: "bool" }        Property { name: "deflate"; type: "bool" }        Property { name: "extract"; type: "bool" }        Signal { name: "showIndicatorChanged" }    }    Component {        name: "Ubuntu::DownloadManager::SingleDownload"        prototype: "QObject"        exports: ["SingleDownload 0.1"]        exportMetaObjectRevisions: [0]        Property { name: "autoStart"; type: "bool" }        Property { name: "errorMessage"; type: "string"; isReadonly: true }        Property { name: "isCompleted"; type: "bool"; isReadonly: true }        Property { name: "downloadInProgress"; type: "bool"; isReadonly: true }        Property { name: "allowMobileDownload"; type: "bool" }        Property { name: "throttle"; type: "qulonglong" }        Property { name: "progress"; type: "int"; isReadonly: true }        Property { name: "downloading"; type: "bool"; isReadonly: true }        Property { name: "downloadId"; type: "string"; isReadonly: true }        Property { name: "headers"; type: "QVariantMap" }        Property { name: "metadata"; type: "Ubuntu::DownloadManager::Metadata"; isPointer: true }        Signal {            name: "canceled"            Parameter { name: "success"; type: "bool" }        }        Signal {            name: "finished"            Parameter { name: "path"; type: "string" }        }        Signal {            name: "paused"            Parameter { name: "success"; type: "bool" }        }        Signal {            name: "processing"            Parameter { name: "path"; type: "string" }        }        Signal {            name: "progressReceived"            Parameter { name: "received"; type: "qulonglong" }            Parameter { name: "total"; type: "qulonglong" }        }        Signal {            name: "resumed"            Parameter { name: "success"; type: "bool" }        }        Signal {            name: "started"            Parameter { name: "success"; type: "bool" }        }        Signal {            name: "errorFound"            Parameter { name: "error"; type: "DownloadError&" }        }        Signal { name: "errorChanged" }        Method {            name: "registerError"            Parameter { name: "error"; type: "Error"; isPointer: true }        }        Method {            name: "bindDownload"            Parameter { name: "download"; type: "Download"; isPointer: true }        }        Method {            name: "unbindDownload"            Parameter { name: "download"; type: "Download"; isPointer: true }        }        Method {            name: "onFinished"            Parameter { name: "path"; type: "string" }        }        Method {            name: "onProgress"            Parameter { name: "received"; type: "qulonglong" }            Parameter { name: "total"; type: "qulonglong" }        }        Method {            name: "onPaused"            Parameter { name: "wasPaused"; type: "bool" }        }        Method {            name: "onResumed"            Parameter { name: "wasResumed"; type: "bool" }        }        Method {            name: "onStarted"            Parameter { name: "wasStarted"; type: "bool" }        }        Method {            name: "onCanceled"            Parameter { name: "wasCanceled"; type: "bool" }        }        Method { name: "start" }        Method { name: "pause" }        Method { name: "resume" }        Method { name: "cancel" }        Method {            name: "download"            Parameter { name: "url"; type: "string" }        }    }    Component {        name: "Ubuntu::DownloadManager::UbuntuDownloadManager"        prototype: "QObject"        exports: ["DownloadManager 0.1"]        exportMetaObjectRevisions: [0]        Property { name: "autoStart"; type: "bool" }        Property { name: "cleanDownloads"; type: "bool" }        Property { name: "errorMessage"; type: "string"; isReadonly: true }        Property { name: "downloads"; type: "QVariantList"; isReadonly: true }        Signal { name: "errorChanged" }        Method {            name: "download"            Parameter { name: "url"; type: "string" }        }    }}

在今天的例子里，我们将使用SingleDownload来下载我们所需要的图片。我们可以看到，SingleDownload有“finished”信号，我们可以通过这个信号来得到文件下载完毕的通知，并在“path”中得到我们所下载文件的路径。当然我们也可以使用其它的信号来得到下载的更多的信息。

我们来修改我们的“Main.qml”如下：

import QtQuick 2.0import Ubuntu.Components 1.1import Ubuntu.DownloadManager 0.1/*!    \brief MainView with a Label and Button elements.*/MainView {    // objectName for functional testing purposes (autopilot-qt5)    objectName: "mainView"    // Note! applicationName needs to match the "name" field of the click manifest    applicationName: "download.liu-xiao-guo"    /*     This property enables the application to change orientation     when the device is rotated. The default is false.    */    //automaticOrientation: true    // Removes the old toolbar and enables new features of the new header.    useDeprecatedToolbar: false    width: units.gu(50)    height: units.gu(75)    Page {        title: i18n.tr("Download")        Rectangle {            width: parent.width            height: units.gu(20)            TextField {                id: text                placeholderText: "File URL to download..."                height: units.gu(5)                anchors {                    left: parent.left                    right: button.left                    rightMargin: units.gu(2)                }                text: "http://bbs.unpcn.com/attachment.aspx?attachmentid=3820584"            }            Button {                id: button                text: "Download"                height: 50                anchors.right: parent.right                anchors.verticalCenter: text.verticalCenter                onClicked: {                    single.download(text.text);                }            }            TextField {                id: downloaded                placeholderText: "Downloaded file address"                height: 100                anchors {                    left: parent.left                    right: parent.right                    top: button.bottom                    rightMargin: units.gu(2)                    topMargin: units.gu(1)                }            }            ProgressBar {                id: progress                minimumValue: 0                maximumValue: 100                value: single.progress                anchors {                    left: parent.left                    right: parent.right                    bottom: parent.bottom                }                SingleDownload {                    id: single                    onFinished: {                        downloaded.text = path;                        console.log("downloaded path: " + path);                    }                }            }            Image {                anchors.top: progress.bottom                source: downloaded.text            }        }    }}

界面非常简单，我们在上面可以输入我们想要的URL文件地址，在下面显示下载后的文件的路径。我们可以点击“Download”按钮来下载我们所需要的文件。为了说明问题，我们在下面使用了一个Image来显示下载的图片：

所有的源码在：https://github.com/liu-xiao-guo/download