Refreshing Konva shape state in Vue component

Question

After dragging and releasing a shape I want it to snap to a close by position. To test this I create a shape at {x:100, y:100}, then drag it and it does snap to 0,0, but only the first time Im dragging it. Next time it will ignore me setting x,y.

I might be missing something basic here? Maybe I am not mutating store the right way. In the below code you can see three attempts to set x and y in handleDragend.

<template>
  <div>
    <v-stage
      ref="stage"
      :config="configKonva"
      @dragstart="handleDragstart"
      @dragend="handleDragend"
    >
      <v-layer ref="layer">
        <v-regular-polygon
          v-for="item in list"
          :key="item.id"        
          :config="{  
            x: item.x,
            y: item.y,
            sides: 6,
            rotation: item.rotation,
            id: item.id,
            radius: 50,
            outerRadius: 50,
            fill: 'green',
            draggable: true,
          }"
        ></v-regular-polygon>
      </v-layer>
    </v-stage>
  </div>
</template>

<script>

const width = window.innerWidth;
const height = window.innerHeight;

export default {
  data() {
    return {
      list: [],
      dragItemId: null,
      configKonva: {
        width: width,
        height: height,       
      }
    };
  },
  methods: {
    handleDragstart(e) {
        //
    },
    handleDragend(e) {
        let item = this.list.find(i => i.id === e.target.id());

        let snapTo = { x: 0, y: 0}

        // Attempt 1
        Vue.set(this.list, 0, {
            ...item,
            x: snapTo.x,
            y: snapTo.y,
        })

        // Attempt 2    
        this.list = this.list.map(function(shape) {
            if(shape.id === item.id) {
                return {
                    ...item,
                    x: snapTo.x,
                    y: snapTo.y,
                }
            }
        })
    },
  },

  mounted() {
    this.list.push({
        id: 1,
        x: 100,
        y: 100,
    });
  }
};
</script>

score 1 · Accepted Answer · answered Mar 24 '20 at 17:11

vue-konva updates nodes ONLY when you have changes in your template.

On the first snap, the coordinated in the template (and store) are changed from {100, 100} to {0, 0}.

When you drag the node the second time, the store still keeps {0, 0} in memory. So no changes are triggered and the node is not moved back.

There are two ways to solve the issue:

(1) Update Konva node position manually

handleDragend(e) {
      let item = this.list.find(i => i.id === e.target.id());

      let snapTo = { x: 0, y: 0 };
      e.target.position(snapTo);
      e.target.getLayer().batchDraw();
      Vue.set(this.list, 0, {
        ...item,
        x: snapTo.x,
        y: snapTo.y
      });
}

(2) Keep the store in sync with node position

You may need to register all position changes into the store:

handleDragMove(e) {
      // do this on every "dragmove"
      let item = this.list.find(i => i.id === e.target.id());

      Vue.set(this.list, 0, {
        ...item,
        x: e.target.x(),
        y: e.target.y()
      });
}

Demo: https://codesandbox.io/s/nifty-northcutt-v52ue

Refreshing Konva shape state in Vue component

1 Answers1

(1) Update Konva node position manually

(2) Keep the store in sync with node position