Java 拖放中的NPE
我在WindowsJVM7_25中测试了这段代码,它运行得很好Java 拖放中的NPE,java,javafx-2,javafx,parseint,javafx-8,Java,Javafx 2,Javafx,Parseint,Javafx 8,我在WindowsJVM7_25中测试了这段代码,它运行得很好 import java.util.Random; import javafx.application.Application; import javafx.collections.ObservableList; import javafx.event.EventHandler; import javafx.scene.Node; import javafx.scene.Scene; import javafx
import java.util.Random;
import javafx.application.Application;
import javafx.collections.ObservableList;
import javafx.event.EventHandler;
import javafx.scene.Node;
import javafx.scene.Scene;
import javafx.scene.input.ClipboardContent;
import javafx.scene.input.DragEvent;
import javafx.scene.input.Dragboard;
import javafx.scene.input.MouseEvent;
import javafx.scene.input.TransferMode;
import javafx.scene.layout.BorderPane;
import javafx.scene.layout.FlowPane;
import javafx.scene.layout.Pane;
import javafx.stage.Stage;
public class DraggableFlowPane extends Application {
@Override
public void start(Stage primaryStage) {
final FlowPane root = new FlowPane();
final Random rng = new Random();
final int NUM_NODES = 120;
for (int i = 0; i < NUM_NODES; i++) {
int red = rng.nextInt(256);
int green = rng.nextInt(256);
int blue = rng.nextInt(256);
Node node = createNode();
node.setStyle(String.format("-fx-background-color: rgb(%d, %d, %d);", red, green, blue));
root.getChildren().add(node);
}
primaryStage.setScene(new Scene(root, 600, 500));
primaryStage.show();
}
private Node createNode() {
final BorderPane bp = new BorderPane();
bp.setOnDragDetected(new EventHandler<MouseEvent>() {
@Override
public void handle(MouseEvent event) {
Dragboard db = bp.startDragAndDrop(TransferMode.MOVE);
ClipboardContent clipboard = new ClipboardContent();
final int nodeIndex = bp.getParent().getChildrenUnmodifiable()
.indexOf(bp);
clipboard.putString(Integer.toString(nodeIndex));
db.setContent(clipboard);
event.consume();
}
});
bp.setOnDragOver(new EventHandler<DragEvent>() {
@Override
public void handle(DragEvent event) {
boolean accept = true;
final Dragboard dragboard = event.getDragboard();
if (dragboard.hasString()) {
int incomingIndex = Integer.parseInt(dragboard.getString());
int myIndex = bp.getParent().getChildrenUnmodifiable()
.indexOf(bp);
if (incomingIndex == myIndex) {
accept = false;
}
} else {
accept = false;
}
if (accept) {
event.acceptTransferModes(TransferMode.MOVE);
}
}
});
bp.setOnDragDropped(new EventHandler<DragEvent>() {
@Override
public void handle(DragEvent event) {
boolean success = false;
final Dragboard dragboard = event.getDragboard();
if (dragboard.hasString()) {
int incomingIndex = Integer.parseInt(dragboard.getString());
final Pane parent = (Pane) bp.getParent();
final ObservableList<Node> children = parent.getChildren();
int myIndex = children.indexOf(bp);
final int laterIndex = Math.max(incomingIndex, myIndex);
Node removedLater = children.remove(laterIndex);
final int earlierIndex = Math.min(incomingIndex, myIndex);
Node removedEarlier = children.remove(earlierIndex);
children.add(earlierIndex, removedLater);
children.add(laterIndex, removedEarlier);
success = true;
}
event.setDropCompleted(success);
}
});
bp.setMinSize(50, 50);
return bp;
}
public static void main(String[] args) {
launch(args);
}
}
(及更多)
int incomingIndex=Integer.parseInt(dragboard.getString())的内容代码>为空
您能告诉我如何解决此问题或重写代码吗?您似乎将null
作为int传递,并且null
无法转换为整数(或int)
检查dragboard.getString()
的输出,检查dragboard.hastring()
。如果dragboard.getString()
为空,它肯定应该返回FALSE
。因此,您永远不会到达intincomingindex=Integer.parseInt(dragboard.getString())代码>,因为如果(dragboard.hastring())
如果找不到问题,请粘贴Dragboard
类实现
编辑:
那么这将更加健壮:
private Node createNode() {
final BorderPane bp = new BorderPane();
bp.setOnDragDetected(new EventHandler<MouseEvent>() {
@Override
public void handle(MouseEvent event) {
Dragboard db = bp.startDragAndDrop(TransferMode.MOVE);
ClipboardContent clipboard = new ClipboardContent();
final int nodeIndex = bp.getParent().getChildrenUnmodifiable()
.indexOf(bp);
clipboard.putString(Integer.toString(nodeIndex));
db.setContent(clipboard);
event.consume();
}
});
bp.setOnDragOver(new EventHandler<DragEvent>() {
@Override
public void handle(DragEvent event) {
boolean accept = true;
final Dragboard dragboard = event.getDragboard();
if (dragboard.hasString()) {
try {
int incomingIndex = Integer.parseInt(dragboard.getString());
int myIndex = bp.getParent().getChildrenUnmodifiable()
.indexOf(bp);
if (incomingIndex == myIndex) {
accept = false;
}
} catch(java.lang.NumberFormatException e) {
//handle null or not number string in clipboard
accept = false;
}
} else {
accept = false;
}
if (accept) {
event.acceptTransferModes(TransferMode.MOVE);
}
}
});
bp.setOnDragDropped(new EventHandler<DragEvent>() {
@Override
public void handle(DragEvent event) {
boolean success = false;
final Dragboard dragboard = event.getDragboard();
if (dragboard.hasString()) {
try {
int incomingIndex = Integer.parseInt(dragboard.getString());
final Pane parent = (Pane) bp.getParent();
final ObservableList<Node> children = parent.getChildren();
int myIndex = children.indexOf(bp);
final int laterIndex = Math.max(incomingIndex, myIndex);
Node removedLater = children.remove(laterIndex);
final int earlierIndex = Math.min(incomingIndex, myIndex);
Node removedEarlier = children.remove(earlierIndex);
children.add(earlierIndex, removedLater);
children.add(laterIndex, removedEarlier);
success = true;
} catch(java.lang.NumberFormatException e) {
//handle null or not number string in clipboard
}
}
event.setDropCompleted(success);
}
});
bp.setMinSize(50, 50);
return bp;
}
专用节点createNode(){
最终边界窗格bp=新边界窗格();
检测到bp.setOnDragDetected(新的EventHandler(){
@凌驾
公共无效句柄(MouseEvent事件){
Dragboard db=bp.startDragAndDrop(TransferMode.MOVE);
剪贴板内容剪贴板=新的剪贴板内容();
final int nodeIndex=bp.getParent().getChildrenUnmodifiable()
.indexOf(bp);
clipboard.putString(Integer.toString(nodeIndex));
db.setContent(剪贴板);
event.consume();
}
});
setOnDragOver(新的EventHandler(){
@凌驾
公共无效句柄(DrageEvent事件){
布尔接受=真;
最终Dragboard Dragboard=event.getDragboard();
if(dragboard.hastring()){
试一试{
int incomingIndex=Integer.parseInt(dragboard.getString());
int myIndex=bp.getParent().getChildrenUnmodifiable()
.indexOf(bp);
如果(incomingIndex==myIndex){
接受=错误;
}
}catch(java.lang.numberformatexe){
//处理剪贴板中的空或非数字字符串
接受=错误;
}
}否则{
接受=错误;
}
如果(接受){
event.acceptTransferModes(TransferMode.MOVE);
}
}
});
setOnDragDrop(新的EventHandler(){
@凌驾
公共无效句柄(DrageEvent事件){
布尔成功=假;
最终Dragboard Dragboard=event.getDragboard();
if(dragboard.hastring()){
试一试{
int incomingIndex=Integer.parseInt(dragboard.getString());
最终窗格父项=(窗格)bp.getParent();
最终ObservableList children=parent.getChildren();
int-myIndex=children.indexOf(bp);
最终int laterIndex=Math.max(收入指数,我的指数);
Node removedLater=子级。移除(laterIndex);
最终int-earlierIndex=Math.min(incomingIndex,myIndex);
Node RemovedPrevior=子级。移除(earlierIndex);
添加(早期索引,稍后删除);
添加(laterIndex,RemovedPrevious);
成功=真实;
}catch(java.lang.numberformatexe){
//处理剪贴板中的空或非数字字符串
}
}
事件。setDropCompleted(成功);
}
});
bp.setMinSize(50,50);
返回bp;
}
彼得
我通过这个链接来了解更多关于拖放功能的信息。
从他们给出的例子来看,你似乎做了预期的事情
进入您的实际代码:
我将尝试理解我是否将null放入setOnDragDetected({})中的ClipboardContent对象中;
ClipboardContent类扩展了HashMap-
如果您试图获取的nodeIndex不是DataFormat.PLAIN_文本,则剪贴板.putString()可能不会实际将索引放入hashmap中。请参阅javadoc中的语句-“将此值设置为null将有效地将其从剪贴板中清除”,并确认是否没有发生这种情况
如果“put”操作成功,putString方法将布尔值返回为True
我将打印这两个内容(“putString()”的输出和“nodeIndex”的值),以调查出了什么问题
-问候,,
Ravi.NPE是一种不相信你的程序的笑话。我会首先制作一个简化的示例,并突出显示令人不快的行。我得到“java.lang.NumberFormatException:null”它看起来像是一个bug或剪贴板实现中的行为差异,这在不同的平台上是不同的=>提交关于Jira的错误报告。dragboard.getString()的内容在null
中,这就是异常发生的原因。您需要找出它为什么为null
。但这是另一个问题,至少你可以确认NPE。不,我不明白为什么它可以在windows上工作,但不能在linux上工作。也许您可以将代码“开销”减少到一个小样本来重现错误。示例越小,我们越容易找到问题/原因。然后用较小的示例打开另一个问题,再试试运气;)Dragboard是JavaFX包的一部分,我无法编辑此代码。还有其他解决方案吗?例如,我可以实现t吗
int incomingIndex = Integer.parseInt(dragboard.getString());
private Node createNode() {
final BorderPane bp = new BorderPane();
bp.setOnDragDetected(new EventHandler<MouseEvent>() {
@Override
public void handle(MouseEvent event) {
Dragboard db = bp.startDragAndDrop(TransferMode.MOVE);
ClipboardContent clipboard = new ClipboardContent();
final int nodeIndex = bp.getParent().getChildrenUnmodifiable()
.indexOf(bp);
clipboard.putString(Integer.toString(nodeIndex));
db.setContent(clipboard);
event.consume();
}
});
bp.setOnDragOver(new EventHandler<DragEvent>() {
@Override
public void handle(DragEvent event) {
boolean accept = true;
final Dragboard dragboard = event.getDragboard();
if (dragboard.hasString()) {
try {
int incomingIndex = Integer.parseInt(dragboard.getString());
int myIndex = bp.getParent().getChildrenUnmodifiable()
.indexOf(bp);
if (incomingIndex == myIndex) {
accept = false;
}
} catch(java.lang.NumberFormatException e) {
//handle null or not number string in clipboard
accept = false;
}
} else {
accept = false;
}
if (accept) {
event.acceptTransferModes(TransferMode.MOVE);
}
}
});
bp.setOnDragDropped(new EventHandler<DragEvent>() {
@Override
public void handle(DragEvent event) {
boolean success = false;
final Dragboard dragboard = event.getDragboard();
if (dragboard.hasString()) {
try {
int incomingIndex = Integer.parseInt(dragboard.getString());
final Pane parent = (Pane) bp.getParent();
final ObservableList<Node> children = parent.getChildren();
int myIndex = children.indexOf(bp);
final int laterIndex = Math.max(incomingIndex, myIndex);
Node removedLater = children.remove(laterIndex);
final int earlierIndex = Math.min(incomingIndex, myIndex);
Node removedEarlier = children.remove(earlierIndex);
children.add(earlierIndex, removedLater);
children.add(laterIndex, removedEarlier);
success = true;
} catch(java.lang.NumberFormatException e) {
//handle null or not number string in clipboard
}
}
event.setDropCompleted(success);
}
});
bp.setMinSize(50, 50);
return bp;
}