修复：picker中值变了后未更新picker-colum中的值 (#23)

* 修复：picker中值变了后未更新picker-colum中的值

packages/image-preview/src/image-preview.js

@@ -16,6 +16,7 @@ var ImagePreviewBox = images => {
     initInstance();
   }
 
+  /* istanbul ignore else */
   if (!instance.value) {
     instance.images = images;
 

packages/picker/src/picker-column.vue

@@ -69,10 +69,14 @@ export default {
       this.currentValues = val;
     },
     currentValues(val) {
+      /* istanbul ignore else */
       if (this.valueIndex === -1) {
         this.currentValue = (val || [])[0];
       }
     },
+    value(val) {
+      this.currentValue = val;
+    },
     currentValue(val) {
       this.doOnValueChange();
 

test/unit/specs/pciker.spec.js

@@ -170,6 +170,25 @@ describe('PickerColumn', () => {
     expect(wrapper.vm.dragRange[1]).to.equal(2 * itemHeight);
   });
 
+  it('change picker-column value', (done) => {
+    wrapper = mount(PickerColumn, {
+      propsData: {
+        values: [1, 2, 3, 4, 5],
+        value: 1
+      }
+    });
+    
+    expect(wrapper.hasClass('van-picker-column')).to.be.true;
+    expect(wrapper.vm.values.length).to.equal(5);
+
+    wrapper.vm.value = 3;
+    wrapper.update();
+    wrapper.vm.$nextTick(() => {
+      expect(wrapper.vm.currentValue).to.equal(3);
+      done();
+    });
+  });
+
   it('change picker-column values', (done) => {
     wrapper = mount(PickerColumn);