Add focus and key events handling on Buttton plasma component

- When a button is clicked it aqcuires the focus.
- The space and return keys now can be used to press the button if
  it has the activeFocus

Signed-off-by: Daker Fernandes Pinheiro <dakerfp@gmail.com>

declarativeimports/plasmacomponents/Button.qml

@@ -36,9 +36,45 @@ Item {
     // Plasma API
     property QtObject theme: PlasmaCore.Theme { }
 
+    function pressButton() {
+        surface.prefix = "pressed";
+    }
+
+    function releaseButton() {
+        if (button.checkable)
+            button.checked = !button.checked;
+
+        // TODO: "checked" state must have special graphics?
+        if (button.checked)
+            surface.prefix = "pressed";
+        else
+            surface.prefix = "normal";
+
+        button.clicked();
+        button.forceActiveFocus();
+    }
+
     width: 50
     height: 20
 
+    Keys.onSpacePressed: pressButton();
+    Keys.onReturnPressed: pressButton();
+    Keys.onReleased: {
+        if (event.key == Qt.Key_Space ||
+            event.key == Qt.Key_Return)
+            releaseButton();
+    }
+
+    onActiveFocusChanged: {
+        if (activeFocus) {
+            shadow.opacity = 0;
+            hover.opacity = 1;
+        }else {
+            shadow.opacity = 1;
+            hover.opacity = 0;
+        }
+    }
+
     PlasmaCore.FrameSvgItem {
         id: hover
 
@@ -125,27 +161,23 @@ Item {
         hoverEnabled: true
 
         onPressed: {
-            surface.prefix = "pressed";
+            pressButton();
         }
         onReleased: {
-            if (button.checkable)
-                button.checked = !button.checked;
-
-            // TODO: "checked" state must have special graphics?
-            if (button.checked)
-                surface.prefix = "pressed";
-            else
-                surface.prefix = "normal";
-
-            button.clicked();
+            releaseButton();
         }
         onEntered: {
             shadow.opacity = 0;
             hover.opacity = 1;
         }
         onExited: {
-            shadow.opacity = 1;
-            hover.opacity = 0;
+            if (button.activeFocus) {
+                shadow.opacity = 0;
+                hover.opacity = 1;
+            } else {
+                shadow.opacity = 1;
+                hover.opacity = 0;
+            }
         }
     }
 }

declarativeimports/test/gallery/Buttons.qml

@@ -29,6 +29,7 @@ Column {
     }
 
     PlasmaComponents.Button {
+        id: bt1
         width: 140
         height: 30
         text: "Button"
@@ -36,9 +37,12 @@ Column {
         onClicked: {
             console.log("Clicked");
         }
+
+        Keys.onTabPressed: bt2.forceActiveFocus();
     }
 
     PlasmaComponents.Button {
+        id: bt2
         width: 140
         height: 30
         text: "Checkable Button"
@@ -50,9 +54,12 @@ Column {
             else
                 console.log("Button Unchecked");
         }
+
+        Keys.onTabPressed: bt3.forceActiveFocus();
     }
 
     PlasmaComponents.Button {
+        id: bt3
         width: 140
         height: 30
         text: "Different Font"
@@ -60,18 +67,26 @@ Column {
             pixelSize: 20
             family: "Helvetica"
         }
+
+        Keys.onTabPressed: bt4.forceActiveFocus();
     }
 
     PlasmaComponents.Button {
+        id: bt4
         width: 140
         height: 30
         text: "Icon Button"
         iconSource: "/home/dakerfp/work/comics-reader/ui/images/random.png"
+
+        Keys.onTabPressed: bt5.forceActiveFocus();
     }
 
     PlasmaComponents.Button {
+        id: bt5
         width: 140
         height: 30
         iconSource: "/home/dakerfp/work/comics-reader/ui/images/random.png"
+
+        Keys.onTabPressed: bt1.forceActiveFocus();
     }
 }