Merge pull request #1903 from fyne-io/fix/1893

Fix issue with Focus call crashing

internal/driver/glfw/canvas.go

@@ -84,12 +84,16 @@ func (c *glCanvas) Focus(obj fyne.Focusable) {
 	c.RUnlock()
 
 	for _, mgr := range focusMgrs {
+		if mgr == nil {
+			continue
+		}
 		if focusMgr != mgr {
 			if mgr.Focus(obj) {
 				return
 			}
 		}
 	}
+
 	fyne.LogError("Failed to focus object which is not part of the canvas’ content, menu or overlays.", nil)
 }
 
@@ -452,7 +456,14 @@ func (c *glCanvas) paint(size fyne.Size) {
 func (c *glCanvas) setContent(content fyne.CanvasObject) {
 	c.content = content
 	c.contentTree = &renderCacheTree{root: &renderCacheNode{obj: c.content}}
+	var focused fyne.Focusable
+	if c.contentFocusMgr != nil {
+		focused = c.contentFocusMgr.Focused() // keep old focus if possible
+	}
 	c.contentFocusMgr = app.NewFocusManager(c.content)
+	if focused != nil {
+		c.contentFocusMgr.Focus(focused)
+	}
 }
 
 func (c *glCanvas) setDirty(dirty bool) {

internal/driver/glfw/canvas_test.go

@@ -204,6 +204,27 @@ func TestGlCanvas_Focus(t *testing.T) {
 	assert.True(t, o2e.focused)
 }
 
+func TestGlCanvas_Focus_BeforeVisible(t *testing.T) {
+	w := createWindow("Test")
+	w.SetPadded(false)
+	e := widget.NewEntry()
+	c := w.Canvas().(*glCanvas)
+	c.Focus(e) // this crashed in the past
+}
+
+func TestGlCanvas_Focus_SetContent(t *testing.T) {
+	w := createWindow("Test")
+	w.SetPadded(false)
+	e := widget.NewEntry()
+	w.SetContent(container.NewHBox(e))
+	c := w.Canvas().(*glCanvas)
+	c.Focus(e)
+	assert.Equal(t, e, c.Focused())
+
+	w.SetContent(container.NewVBox(e))
+	assert.Equal(t, e, c.Focused())
+}
+
 func TestGlCanvas_FocusHandlingWhenAddingAndRemovingOverlays(t *testing.T) {
 	w := createWindow("Test")
 	w.SetPadded(false)