fix(Picker): make sure confirm params' behavior consistent (#13423) (#13425)

Signed-off-by: Kayne <w.zengkai@gmail.com>

packages/vant/src/picker/Picker.tsx

@@ -147,7 +147,9 @@ export default defineComponent({
     };
 
     const getEventParams = () => ({
-      selectedValues: selectedValues.value.slice(0),
+      selectedValues: selectedValues.value.length
+        ? selectedValues.value.slice(0)
+        : resetSelectedValues(currentColumns.value),
       selectedOptions: selectedOptions.value,
       selectedIndexes: selectedIndexes.value,
     });
@@ -268,23 +270,20 @@ export default defineComponent({
       }
     };
 
-    watch(
+    const resetSelectedValues = (columns: PickerColumn[]) => {
-      currentColumns,
-      (columns) => {
       columns.forEach((options, index) => {
         if (
           options.length &&
           !isOptionExist(options, selectedValues.value[index], fields.value)
         ) {
-            setValue(
+          setValue(index, getFirstEnabledOption(options)![fields.value.value]);
-              index,
-              getFirstEnabledOption(options)![fields.value.value],
-            );
         }
       });
-      },
+    };
-      { immediate: true },
+
-    );
+    watch(currentColumns, (columns) => resetSelectedValues(columns), {
+      immediate: true,
+    });
 
     // preserve last emitted model value
     // when props.modelValue is updated by parent component,

packages/vant/src/picker/test/index.spec.tsx

@@ -489,3 +489,35 @@ test('should emit correct values when clicking confirm button during column scro
     },
   ]);
 });
+
+test('should emit default values when clear modelValue', async () => {
+  const columns = [
+    { text: '1', value: '1' },
+    { text: '2', value: '2' },
+  ];
+  const wrapper = mount({
+    setup() {
+      const modelValue = ref(['1']);
+      return () => (
+        <>
+          <button
+            class="clear-button"
+            onClick={() => (modelValue.value = [])}
+          />
+          <Picker v-model={modelValue.value} columns={columns} />
+        </>
+      );
+    },
+  });
+  const button = wrapper.find('.clear-button');
+  await button.trigger('click');
+  const picker = wrapper.findComponent(Picker);
+  await picker.find('.van-picker__confirm').trigger('click');
+  expect(picker.emitted('confirm')![0]).toEqual([
+    {
+      selectedOptions: [{ text: '1', value: '1' }],
+      selectedValues: ['1'],
+      selectedIndexes: [0],
+    },
+  ]);
+});