Requirement Description
In List components, when both drag functionality and long-press functionality are set for a single ListItem, conflicts occur during actual operation. How to resolve the conflict between drag and long-press functions on a single ListItem?
Background Knowledge
- Unified Drag Support provides a mechanism for transferring data via mouse or touchscreen gestures, where data is dragged from one component position to another to trigger responses.
- Long Press Gesture triggers long-press events by holding the screen.
- Since both drag events and long-press gestures are triggered by holding, this type of combined gesture creates conflicts. For example, when each ListItem in a List component has its own long-press event, drag functionality conflicts with long-press gesture functionality.
- Grid is a grid container composed of cells divided by “rows” and “columns”, enabling various layouts by specifying cell positions for items.
- Swipe gesture PanGesture provides functionality for custom drag events.
Implementation Steps
Since setting individual long-press events in ListItem conflicts with drag events, it’s recommended to abandon the List’s native drag events and instead use PanGesture to manually implement drag logic. Then use combined gestures to implement other long-press events.
Code Snippet / Configuration
import curves from '@ohos.curves';
@Entry
@Component
struct Page {
// Element array
@State numbers: number[] = [];
// Multiple columns
private str: string = '';
row: number = 4;
// Index of the last element in the array of elements
@State lastIndex: number = 0;
@State dragItem: number = -1;
@State scaleItem: number = -1;
item: number = -1;
private dragRefOffsetX: number = 0;
private dragRefOffsetY: number = 0;
@State offsetX: number = 0;
@State offsetY: number = 0;
private FIX_VP_X: number = 108;
private FIX_VP_Y: number = 120;
aboutToAppear() {
for (let i = 1; i <= 36; i++) {
this.numbers.push(i);
}
this.lastIndex = this.numbers.length - 1;
// Multiple columns
for (let i = 0; i < this.row; i++) {
this.str = this.str + '1fr ';
}
}
itemMove(index: number, newIndex: number): void {
console.info('index:' + index + ' newIndex:' + newIndex);
if (!this.isDraggable(newIndex)) {
return;
}
let tmp = this.numbers.splice(index, 1);
this.numbers.splice(newIndex, 0, tmp[0]);
}
// Swipe down
down(index: number): void {
if (!this.isDraggable(index + this.row)) {
return;
}
this.offsetY -= this.FIX_VP_Y;
this.dragRefOffsetY += this.FIX_VP_Y;
// Multiple columns
this.itemMove(index, index + this.row);
}
// Swipe down (the bottom right corner is empty)
down2(index: number): void {
if (!this.isDraggable(index + 3)) {
return;
}
this.offsetY -= this.FIX_VP_Y;
this.dragRefOffsetY += this.FIX_VP_Y;
this.itemMove(index, index + 3);
}
// Swipe up
up(index: number): void {
if (!this.isDraggable(index - this.row)) {
return;
}
this.offsetY += this.FIX_VP_Y;
this.dragRefOffsetY -= this.FIX_VP_Y;
this.itemMove(index, index - this.row);
}
// Swipe left
left(index: number): void {
if (!this.isDraggable(index - 1)) {
return;
}
this.offsetX += this.FIX_VP_X;
this.dragRefOffsetX -= this.FIX_VP_X;
this.itemMove(index, index - 1);
}
// Swipe right
right(index: number): void {
if (!this.isDraggable(index + 1)) {
return;
}
this.offsetX -= this.FIX_VP_X;
this.dragRefOffsetX += this.FIX_VP_X;
this.itemMove(index, index + 1);
}
// Swipe right
lowerRight(index: number): void {
if (!this.isDraggable(index + this.row + 1)) {
return;
}
this.offsetX -= this.FIX_VP_X;
this.dragRefOffsetX += this.FIX_VP_X;
this.offsetY -= this.FIX_VP_Y;
this.dragRefOffsetY += this.FIX_VP_Y;
this.itemMove(index, index + this.row + 1);
}
// Swipe up to the right
upperRight(index: number): void {
if (!this.isDraggable(index - (this.row - 1))) {
return;
}
this.offsetX -= this.FIX_VP_X;
this.dragRefOffsetX += this.FIX_VP_X;
this.offsetY += this.FIX_VP_Y;
this.dragRefOffsetY -= this.FIX_VP_Y;
this.itemMove(index, index - (this.row - 1));
}
// Swipe left
lowerLeft(index: number): void {
if (!this.isDraggable(index + (this.row - 1))) {
return;
}
this.offsetX += this.FIX_VP_X;
this.dragRefOffsetX -= this.FIX_VP_X;
this.offsetY -= this.FIX_VP_Y;
this.dragRefOffsetY += this.FIX_VP_Y;
this.itemMove(index, index + (this.row - 1));
}
// Swipe up to the left
upperLeft(index: number): void {
if (!this.isDraggable(index - (this.row + 1))) {
return;
}
this.offsetX += this.FIX_VP_X;
this.dragRefOffsetX -= this.FIX_VP_X;
this.offsetY += this.FIX_VP_Y;
this.dragRefOffsetY -= this.FIX_VP_Y;
this.itemMove(index, index - (this.row + 1));
}
// By using the index of an element, control whether the corresponding element can be moved or sorted.
isDraggable(index: number): boolean {
console.info(`index: ${index}`);
return index > -1; // Always true, all elements are movable and sortable.
}
build() {
Column() {
Grid() {
ForEach(this.numbers, (item: number) => {
GridItem() {
Text(item + '')
.fontSize(12)
.fontColor(Color.Black)
.width('100%')
.textAlign(TextAlign.Center)
.height(30)
.borderRadius(10)
.backgroundColor(0xFFFFFF)
.shadow(this.scaleItem == item ? {
radius: 70,
color: '#15000000',
offsetX: 0,
offsetY: 0
} :
{
radius: 0,
color: '#15000000',
offsetX: 0,
offsetY: 0
})
.animation({ curve: Curve.Sharp, duration: 300 });
}
// Add vibration
.onTouch(() => {
})
.onAreaChange((oldVal, newVal) => {
// Multiple columns
this.FIX_VP_X = Math.round(newVal.width as number);
this.FIX_VP_Y = Math.round(newVal.height as number);
console.info(`oldVal:${JSON.stringify(oldVal)}`);
})
// Specify fixed GridItem to not respond to events
.hitTestBehavior(this.isDraggable(this.numbers.indexOf(item)) ? HitTestMode.Default : HitTestMode.None)
.scale({ x: this.scaleItem == item ? 1.05 : 1, y: this.scaleItem == item ? 1.05 : 1 })
.zIndex(this.dragItem == item ? 1 : 0)
.translate(this.dragItem == item ? { x: this.offsetX, y: this.offsetY } : { x: 0, y: 0 })
.padding(5)
.gesture(
GestureGroup(GestureMode.Sequence,
LongPressGesture({ repeat: true, duration: 50 })
.onAction((event?: GestureEvent) => {
console.info(`event: ${event}`);
this.getUIContext().animateTo({ curve: Curve.Friction, duration: 300 }, () => {
this.scaleItem = item;
});
})
.onActionEnd(() => {
this.getUIContext().animateTo({ curve: Curve.Friction, duration: 300 }, () => {
this.scaleItem = -1;
});
}),
PanGesture({ fingers: 1, direction: null, distance: 0 })
.onActionStart(() => {
this.dragItem = item;
this.dragRefOffsetX = 0;
this.dragRefOffsetY = 0;
})
.onActionUpdate((event: GestureEvent) => {
this.offsetY = event.offsetY - this.dragRefOffsetY;
this.offsetX = event.offsetX - this.dragRefOffsetX;
console.info(`event.offsetY during movement：${event.offsetY}`,
` this.dragRefOffsetY: ${this.dragRefOffsetY}`, `this.offsetY: ${this.offsetY}`);
console.info(`event.offsetX during movement：${event.offsetX}`,
` this.dragRefOffsetX: ${this.dragRefOffsetX}`, `this.offsetX: ${this.offsetX}`);
this.getUIContext().animateTo({ curve: curves.interpolatingSpring(0, 1, 400, 38) }, () => {
let index = this.numbers.indexOf(this.dragItem);
console.info('index= ', index);
if (this.offsetY >= this.FIX_VP_Y / 2 &&
(this.offsetX <= this.FIX_VP_X / 2 && this.offsetX >= -this.FIX_VP_X / 2)
&& (index + this.row <= this.lastIndex)) {
// Swipe down
this.down(index);
} else if (this.offsetY <= -this.FIX_VP_Y / 2 &&
(this.offsetX <= this.FIX_VP_X / 2 && this.offsetX >= -this.FIX_VP_X / 2)
&& index - this.row >= 0) {
// Swipe up
this.up(index);
} else if (this.offsetX >= this.FIX_VP_X / 2 &&
(this.offsetY <= this.FIX_VP_Y / 2 && this.offsetY >= -this.FIX_VP_Y / 2)
&& !(((index - (this.row - 1)) % this.row == 0) || index == this.lastIndex)) {
// Swipe right
this.right(index);
} else if (this.offsetX <= -this.FIX_VP_X / 2 &&
(this.offsetY <= this.FIX_VP_Y / 2 && this.offsetY >= -this.FIX_VP_Y / 2)
&& !(index % this.row == 0)) {
// Swipe left
this.left(index);
} else if (this.offsetX >= this.FIX_VP_X / 2 && this.offsetY >= this.FIX_VP_Y / 2
&& ((index + this.row + 1 <= this.lastIndex && !((index - (this.row - 1)) % this.row == 0)) ||
!((index - (this.row - 1)) % this.row == 0))) {
// Swipe right
this.lowerRight(index);
} else if (this.offsetX >= this.FIX_VP_X / 2 && this.offsetY <= -this.FIX_VP_Y / 2
&& !((index - this.row < 0) || ((index - (this.row - 1)) % this.row == 0))) {
// Swipe up to the right
this.upperRight(index);
} else if (this.offsetX <= -this.FIX_VP_X / 2 && this.offsetY >= this.FIX_VP_Y / 2
&& (!(index % this.row == 0) && (index + (this.row - 1) <= this.lastIndex))) {
// Swipe left
this.lowerLeft(index);
} else if (this.offsetX <= -this.FIX_VP_X / 2 && this.offsetY <= -this.FIX_VP_Y / 2
&& !((index <= this.row - 1) || (index % this.row == 0))) {
// Swipe up to the left
this.upperLeft(index);
} else if (this.offsetX >= this.FIX_VP_X / 2 && this.offsetY >= this.FIX_VP_Y / 2
&& (index == this.lastIndex)) {
// Swipe to the right (the bottom right corner is empty)
this.down2(index);
}
});
})
.onActionEnd(() => {
this.getUIContext().animateTo({ curve: curves.interpolatingSpring(0, 1, 400, 38) }, () => {
this.dragItem = -1;
});
this.getUIContext().animateTo({
curve: curves.interpolatingSpring(14, 1, 170, 17), delay: 150
}, () => {
this.scaleItem = -1;
});
})
)
.onCancel(() => {
this.getUIContext().animateTo({ curve: curves.interpolatingSpring(0, 1, 400, 38) }, () => {
this.dragItem = -1;
});
this.getUIContext().animateTo({
curve: curves.interpolatingSpring(14, 1, 170, 17)
}, () => {
this.scaleItem = -1;
});
})
);
}, (item: number) => item.toString());
}
.width('90%')
.editMode(true)
.scrollBar(BarState.Off)
// Multiple columns
.columnsTemplate(this.str)
}
.expandSafeArea([SafeAreaType.SYSTEM], [SafeAreaEdge.TOP, SafeAreaEdge.BOTTOM])
.width('100%').height('100%').backgroundColor('#f1f3f5').padding({ top: 5 });
}
}
Test Results
Limitations or Considerations
- The current implementation uses fixed threshold values (FIX_VP_X/2 and FIX_VP_Y/2) for gesture detection, which might need adjustment for different screen sizes or grid configurations.
- The solution requires manual implementation of all drag logic, which increases code complexity compared to using native drag functionality.
- Performance considerations should be taken into account when dealing with large datasets, as the current implementation uses frequent state updates and animations.
- The gesture sequencing (LongPressGesture followed by PanGesture) creates a dependency where the pan gesture only activates after a successful long press, which might not be suitable for all use cases.
- Edge case handling for boundary conditions (first row, last row, first column, last column) requires additional logic as demonstrated in the directional movement methods.
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