Java 创建播放器（不播放文件）

我有一个创建视频播放器的类（代码附在下面），这个类只处理视频文件。我想显示没有视频文件的播放器，当我通过公共方法“

setFile

”发送到对象时，它将开始播放

我试图向这个类发送“null”，而不是一个文件，但我得到了一个错误（“

java.lang.NullPointerException

”）

错误是：

Exception in Application start method
java.lang.reflect.InvocationTargetException
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at com.sun.javafx.application.LauncherImpl.launchApplicationWithArgs(Unknown Source)
    at com.sun.javafx.application.LauncherImpl.launchApplication(Unknown Source)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at sun.launcher.LauncherHelper$FXHelper.main(Unknown Source)
Caused by: java.lang.RuntimeException: Exception in Application start method
    at com.sun.javafx.application.LauncherImpl.launchApplication1(Unknown Source)
    at com.sun.javafx.application.LauncherImpl.lambda$launchApplication$152(Unknown Source)
    at com.sun.javafx.application.LauncherImpl$$Lambda$51/1323468230.run(Unknown Source)
    at java.lang.Thread.run(Unknown Source)
Caused by: java.lang.IllegalArgumentException: uri.getScheme() == null! uri == ''
    at com.sun.media.jfxmedia.locator.Locator.<init>(Unknown Source)
    at javafx.scene.media.Media.<init>(Unknown Source)
    at v04.VideoPlayer.setFile(VideoPlayer.java:90)
    at v04.VideoPlayer.<init>(VideoPlayer.java:40)
    at v04.MainFrame.setVideoPlayer(MainFrame.java:218)
    at v04.MainFrame.createVideoPane(MainFrame.java:246)
    at v04.MainFrame.start(MainFrame.java:112)
    at com.sun.javafx.application.LauncherImpl.lambda$launchApplication1$159(Unknown Source)
    at com.sun.javafx.application.LauncherImpl$$Lambda$54/539248128.run(Unknown Source)
    at com.sun.javafx.application.PlatformImpl.lambda$runAndWait$172(Unknown Source)
    at com.sun.javafx.application.PlatformImpl$$Lambda$47/186276003.run(Unknown Source)
    at com.sun.javafx.application.PlatformImpl.lambda$null$170(Unknown Source)
    at com.sun.javafx.application.PlatformImpl$$Lambda$49/1850153616.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at com.sun.javafx.application.PlatformImpl.lambda$runLater$171(Unknown Source)
    at com.sun.javafx.application.PlatformImpl$$Lambda$48/237061348.run(Unknown Source)
    at com.sun.glass.ui.InvokeLaterDispatcher$Future.run(Unknown Source)
    at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
    at com.sun.glass.ui.win.WinApplication.lambda$null$145(Unknown Source)
    at com.sun.glass.ui.win.WinApplication$$Lambda$37/2117255219.run(Unknown Source)

班级：

import java.io.File;

import javafx.beans.property.DoubleProperty;
import javafx.geometry.Insets;
import javafx.geometry.Pos;
import javafx.scene.control.Button;
import javafx.scene.control.Label;
import javafx.scene.control.Slider;
import javafx.scene.layout.BorderPane;
import javafx.scene.layout.GridPane;
import javafx.scene.layout.HBox;
import javafx.scene.layout.Pane;
import javafx.scene.layout.Region;
import javafx.scene.layout.StackPane;
import javafx.scene.media.Media;
import javafx.scene.media.MediaPlayer;
import javafx.scene.media.MediaView;
import javafx.util.Duration;

public class VideoPlayer extends GridPane  {

    File videoFile;
    Media media;
    MediaPlayer mediaPlayer;
    MediaView mediaView;

    DoubleProperty width;
    DoubleProperty height;

    VideoPlayer(File file, double width, double height) {

        setHgap(10);
        setVgap(10);
        setPadding(new Insets(10, 10, 10, 10));

        setFile(file);
        mediaView.setFitHeight(height*0.80);
        mediaView.setFitWidth(width*0.80);
        mediaView.setPreserveRatio(true);


        add(mediaView, 1, 0); 
        add(setSlider(),1,1);

    }

    public HBox setSlider() {

        // Play and pause button
        Button playButton = new Button("Play");
        playButton.setOnAction(e -> {
            if (playButton.getText().equals("Play")) {
                mediaPlayer.play();
                playButton.setText("pause");
            } else {
                mediaPlayer.pause();
                playButton.setText("Play");
            }
        });


        // Rewind button
        Button rewindButton = new Button("rewind");
        rewindButton.setOnAction(e -> mediaPlayer.seek(Duration.ZERO));

        // Slieder for volume
        Slider slVolume = new Slider();
        slVolume.setPrefWidth(150);
        slVolume.setMaxWidth(Region.USE_PREF_SIZE);
        slVolume.setMinWidth(30);
        slVolume.setValue(50);
        mediaPlayer.volumeProperty().bind(slVolume.valueProperty().divide(100));
        HBox hBox = new HBox(10);
        hBox.setAlignment(Pos.CENTER);
        hBox.getChildren().addAll(playButton, rewindButton,
                new Label("Volume"), slVolume);
        return hBox;
    }

    public void setFile(File file) {

        videoFile=file;
        videoFile = file;
        media = new Media(videoFile.toURI().toString());
        mediaPlayer = new MediaPlayer(media);
        mediaView = new MediaView(mediaPlayer);
        width = mediaView.fitWidthProperty();
        height = mediaView.fitHeightProperty();
    }

    public void playVideo() {
        mediaPlayer.play();
    }
}

---

当您将null参数传递给构造函数的第一个参数时，它将作为以下内容传递给setFile:

setFile（null）

此功能具有：

public void setFile(File file) {
    videoFile = file;
    videoFile = file; // You are doing this twice? Is this an error on your part?
    media = new Media(videoFile.toURI().toString()); // This is where the null pointer is happening.
}

videoFile为空，您正在对空对象调用

toURI（）

我不知道这是否能完全解决您的问题，但除非您更改代码，否则您需要像这样防止空值：

public void setFile(File file) {
    if (file == null)
        return;
    videoFile = file;
    media = new Media(videoFile.toURI().toString());
    mediaPlayer = new MediaPlayer(media);
    mediaView = new MediaView(mediaPlayer);
    width = mediaView.fitWidthProperty();
    height = mediaView.fitHeightProperty();
}

---

由于你的英语问题（我无意冒犯），我无法理解你的问题。你能试着把这句话改得更清楚些，让我明白吗？@Water我想在没有视频文件的情况下运行这个类（只显示播放器！）。这是可能的吗？或者给玩家画一个框架…你能发布你的空指针堆栈跟踪和/或告诉我什么是违规的行吗？谢谢，但我想你不明白我的意思。我知道是什么导致了这个错误，我这样做是为了测试。无论如何，我通过一个黑色矩形解决了这个问题，当一个视频文件为空时，这个矩形就会出现。再次感谢！很抱歉，我帮不了你更多的忙，不过很高兴你还是把它修好了！

public void setFile(File file) {
    videoFile = file;
    videoFile = file; // You are doing this twice? Is this an error on your part?
    media = new Media(videoFile.toURI().toString()); // This is where the null pointer is happening.
}

public void setFile(File file) {
    if (file == null)
        return;
    videoFile = file;
    media = new Media(videoFile.toURI().toString());
    mediaPlayer = new MediaPlayer(media);
    mediaView = new MediaView(mediaPlayer);
    width = mediaView.fitWidthProperty();
    height = mediaView.fitHeightProperty();
}