mainwindow.h

private slots:void on_nextBt_clicked();void on_frontBt_clicked();

在mainwindow.cpp中

MainWindow::MainWindow(QWidget *parent) :QMainWindow(parent),ui(new Ui::MainWindow){//切歌存储歌单列表QFileInfoList infolist = dir.entryInfoList();//遍历整个目录，获取所有目录文件foreach(QFileInfo info, infolist){//排除.和..文件if(info.fileName() != "." && info.fileName() != ".."){//把所有歌曲添加进入播放列表playlist.addMedia(QUrl::fromLocalFile(dirpath+info.fileName()));}}
}
//上一首
void MainWindow::on_frontBt_clicked()
{/*------------------------------------------------------------ M_Amount = ui->listWidget->count();//获取歌曲总数量        ----   M_Current = ui->listWidget->currentRow();  //获取当前位置  -----  在这里每次循环的时候，在行列表会重置到原来的位置，所以会出现一直停留在----   上一首中                                                  --------------------------------------------------------------*/if(M_Current == 0){M_Current = ui->listWidget->count() - 1;}else{M_Current--;}QListWidgetItem *item = ui->listWidget->item(M_Current);item->setSelected(true);player.stop();player.setMedia(QUrl::fromLocalFile(dirpath+"/"+item->text()));player.play();
}//下一首
void MainWindow::on_nextBt_clicked()
{//先判断当前位置是否是尾端，如果是，直接置0if(M_Current + 1== ui->listWidget->count()){M_Current = 0;}else{M_Current++;}QListWidgetItem *item = ui->listWidget->item(M_Current);item->setSelected(true);player.stop();player.setMedia(QUrl::fromLocalFile(dirpath+"/"+item->text()));player.play();}

在mainwindow.h

void getState(QMediaPlayer::State state);        //播放和暂停传信号

在mainwindow.cpp

//播放停止合二为一
void MainWindow::on_pushButton_3_clicked()
{if(player.state() == QMediaPlayer::PlayingState){player.pause();}else {player.play();}}
void MainWindow::getState( QMediaPlayer::State state )
{if(state == QMediaPlayer::PlayingState){ui->pushButton_3->setText(" | |");}else{ui->pushButton_3->setText(" 》");}
}