Allow user to specify offset directly

src/widgets/list.rs

@@ -20,13 +20,17 @@ impl Default for ListState {
     fn default() -> ListState {
         ListState {
             offset: 0,
-            target: None,
             selected: BTreeSet::new(),
         }
     }
 }
 
 impl ListState {
+    pub fn offset(mut self, offset: usize) -> Self {
+        self.offset = offset;
+        self
+    }
+    
     pub fn selected(&self) -> &BTreeSet<usize> {
         &self.selected
     }
@@ -35,13 +39,6 @@ impl ListState {
         self.selected.insert(index);
     }
 
-    pub fn front_selection(&mut self) -> Option<usize> {
-        match self.target {
-            None => self.selected.iter().next().cloned(),
-            Some(target) => Some(target),
-        }
-    }
-
     pub fn deselect(&mut self, index: usize) {
         self.selected.remove(&index);
     }
@@ -147,7 +144,6 @@ impl<'a> List<'a> {
 
     fn get_items_bounds(
         &self,
-        selected: Option<usize>,
         offset: usize,
         max_height: usize,
     ) -> (usize, usize) {
@@ -155,6 +151,7 @@ impl<'a> List<'a> {
         let mut start = offset;
         let mut end = offset;
         let mut height = 0;
+
         for item in self.items.iter().skip(offset) {
             if height + item.height() > max_height {
                 break;
@@ -163,23 +160,6 @@ impl<'a> List<'a> {
             end += 1;
         }
 
-        let selected = selected.unwrap_or(0).min(self.items.len() - 1);
-        while selected >= end {
-            height = height.saturating_add(self.items[end].height());
-            end += 1;
-            while height > max_height {
-                height = height.saturating_sub(self.items[start].height());
-                start += 1;
-            }
-        }
-        while selected < start {
-            start -= 1;
-            height = height.saturating_add(self.items[start].height());
-            while height > max_height {
-                end -= 1;
-                height = height.saturating_sub(self.items[end].height());
-            }
-        }
         (start, end)
     }
 }
@@ -207,9 +187,7 @@ impl<'a> StatefulWidget for List<'a> {
         }
         let list_height = list_area.height as usize;
 
-        let (start, end) =
-            self.get_items_bounds(state.front_selection(), state.offset, list_height);
-        state.offset = start;
+        let (start, end) = self.get_items_bounds(state.offset, list_height);
 
         let highlight_symbol = self.highlight_symbol.unwrap_or("");
         let blank_symbol = " ".repeat(highlight_symbol.width());
@@ -220,7 +198,7 @@ impl<'a> StatefulWidget for List<'a> {
             .items
             .iter_mut()
             .enumerate()
-            .skip(state.offset)
+            .skip(start)
             .take(end - start)
         {
             let (x, y) = match self.start_corner {