工作已有一段时间，终于有时间把接触到的各种问题及解决方案记录在博客上了。
废话不多说，开始正文。
由于项目(Qt-5.8.0 + MSVC-2013_x64, Win7 平台)涉及一个图表模块，这个模块需要根据数据生成简单的柱状图。要求代表数据系列的柱子外侧上方显示数据系列的标签，表示当前柱子的数值。
自然而然地，小组成员想到了利用Qt Charts模块完成需求。然而同事发现，以下代码无法将数据系列标签正确地显示于柱子之外的上方。实际上，在同事的机器上，柱状图左侧的数据柱没有显示任何数据系列标签，柱状图右侧的数据柱可以正确显示数据系列标签。
QBarSeries *series = new QBarSeries(); //...
series->setLabelsPosition(QAbstractBarSeries::LabelsOutsideEnd); // 设置数据系列标签的位置于数据柱外侧上方
series->setLabelsVisible(true); //显示数据系列标签
百思不得其解，我在我机器上调试同事的代码，发现我这边居然一个数据系列标签都不显示了。
打开Qt的Examples的BarChart Example并编译运行之。确认是Qt的Bug，和同事的代码无关。同时我在自己的笔记本上Qt-5.10.1运行Qt的这个例子，发现问题依旧。
效果如下图(数据柱中间的小白线就是不正常显示的数据系列标签):
如果拉伸柱状图，直接就看不到数据系列标签了:
但是，只要设置数据系列标签的位置在其它位置(柱子内测上方)，就可以正常显示数据系列标签了:
代码如下:
/**************************************************************************** ** ** Copyright (C) 2016 The Qt Company Ltd. ** Contact: https://www.qt.io/licensing/ ** ** This file is part of the Qt Charts module of the Qt Toolkit. ** ** $QT_BEGIN_LICENSE:GPL$ ** Commercial License Usage ** Licensees holding valid commercial Qt licenses may use this file in ** accordance with the commercial license agreement provided with the ** Software or, alternatively, in accordance with the terms contained in ** a written agreement between you and The Qt Company. For licensing terms ** and conditions see https://www.qt.io/terms-conditions. For further ** information use the contact form at https://www.qt.io/contact-us. ** ** GNU General Public License Usage ** Alternatively, this file may be used under the terms of the GNU ** General Public License version 3 or (at your option) any later version ** approved by the KDE Free Qt Foundation. The licenses are as published by ** the Free Software Foundation and appearing in the file LICENSE.GPL3 ** included in the packaging of this file. Please review the following ** information to ensure the GNU General Public License requirements will ** be met: https://www.gnu.org/licenses/gpl-3.0.html. ** ** $QT_END_LICENSE$ ** ****************************************************************************/ #include <QtWidgets/QApplication> #include <QtWidgets/QMainWindow> #include <QtCharts/QChartView> #include <QtCharts/QBarSeries> #include <QtCharts/QBarSet> #include <QtCharts/QLegend> #include <QtCharts/QBarCategoryAxis> QT_CHARTS_USE_NAMESPACE int main(int argc, char *argv[]) { QApplication a(argc, argv); //![1]
QBarSet *set0 = new QBarSet("Jane"); QBarSet *set1 = new QBarSet("John"); QBarSet *set2 = new QBarSet("Axel"); QBarSet *set3 = new QBarSet("Mary"); QBarSet *set4 = new QBarSet("Samantha"); *set0 << 1 << 2 << 3 << 4 << 5 << 6; *set1 << 5 << 0 << 0 << 4 << 0 << 7; *set2 << 3 << 5 << 8 << 13 << 8 << 5; *set3 << 5 << 6 << 7 << 3 << 4 << 5; *set4 << 9 << 7 << 5 << 3 << 1 << 2; //![1] //![2]
QBarSeries *series = new QBarSeries(); series->append(set0); series->append(set1); series->append(set2); series->append(set3); series->append(set4); series->setLabelsPosition(QAbstractBarSeries::LabelsInsideEnd); // 设置数据系列标签的位置于数据柱内测上方
series->setLabelsVisible(true); // 设置显示数据系列标签 //![2] //![3]
QChart *chart = new QChart(); chart->addSeries(series); chart->setTitle("Simple barchart example"); chart->setAnimationOptions(QChart::SeriesAnimations); //![3] //![4]
QStringList categories; categories << "Jan" << "Feb" << "Mar" << "Apr" << "May" << "Jun"; QBarCategoryAxis *axis = new QBarCategoryAxis(); axis->append(categories); chart->createDefaultAxes(); chart->setAxisX(axis, series); //![4] //![5]
chart->legend()->setVisible(true); chart->legend()->setAlignment(Qt::AlignBottom); //![5] //![6]
QChartView *chartView = new QChartView(chart); chartView->setRenderHint(QPainter::Antialiasing); //![6] //![7]
QMainWindow window; window.setCentralWidget(chartView); window.resize(420, 300); window.show(); //![7]
return a.exec(); }
结论：目前在Qt-5.10.1及以下的Qt版本中，无法让数据系列标签显示在柱状图外侧上方。
如有错误之处还请指正，谢谢！