fix #71, allow Undoing Clear

app/src/main/kotlin/com/simplemobiletools/draw/activities/MainActivity.kt

@@ -25,14 +25,14 @@ import com.simplemobiletools.draw.extensions.config
 import com.simplemobiletools.draw.helpers.JPG
 import com.simplemobiletools.draw.helpers.PNG
 import com.simplemobiletools.draw.helpers.SVG
+import com.simplemobiletools.draw.interfaces.CanvasListener
 import com.simplemobiletools.draw.models.Svg
-import com.simplemobiletools.draw.views.MyCanvas
 import kotlinx.android.synthetic.main.activity_main.*
 import java.io.ByteArrayOutputStream
 import java.io.File
 import java.io.FileOutputStream
 
-class MainActivity : SimpleActivity(), MyCanvas.PathsChangedListener {
+class MainActivity : SimpleActivity(), CanvasListener {
     private val FOLDER_NAME = "images"
     private val FILE_NAME = "simple-draw.png"
 
@@ -329,8 +329,8 @@ class MainActivity : SimpleActivity(), MyCanvas.PathsChangedListener {
         updateEraserState()
     }
 
-    override fun pathsChanged(cnt: Int) {
+    override fun toggleUndoVisibility(visible: Boolean) {
-        undo.beVisibleIf(cnt > 0)
+        undo.beVisibleIf(visible)
     }
 
     private var onStrokeWidthBarChangeListener: SeekBar.OnSeekBarChangeListener = object : SeekBar.OnSeekBarChangeListener {

app/src/main/kotlin/com/simplemobiletools/draw/interfaces/CanvasListener.kt

@@ -0,0 +1,5 @@
+package com.simplemobiletools.draw.interfaces
+
+interface CanvasListener {
+    fun toggleUndoVisibility(visible: Boolean)
+}

app/src/main/kotlin/com/simplemobiletools/draw/views/MyCanvas.kt

@@ -13,6 +13,7 @@ import com.bumptech.glide.request.RequestOptions
 import com.simplemobiletools.commons.extensions.getContrastColor
 import com.simplemobiletools.commons.extensions.toast
 import com.simplemobiletools.draw.R
+import com.simplemobiletools.draw.interfaces.CanvasListener
 import com.simplemobiletools.draw.models.MyParcelable
 import com.simplemobiletools.draw.models.MyPath
 import com.simplemobiletools.draw.models.PaintOptions
@@ -24,7 +25,11 @@ class MyCanvas(context: Context, attrs: AttributeSet) : View(context, attrs) {
 
     var mPaths = LinkedHashMap<MyPath, PaintOptions>()
     var mBackgroundBitmap: Bitmap? = null
-    var mListener: PathsChangedListener? = null
+    var mListener: CanvasListener? = null
+
+    // allow undoing Clear
+    var mLastPaths = LinkedHashMap<MyPath, PaintOptions>()
+    var mLastBackgroundBitmap: Bitmap? = null
 
     private var mPaint = Paint()
     private var mPath = MyPath()
@@ -53,6 +58,15 @@ class MyCanvas(context: Context, attrs: AttributeSet) : View(context, attrs) {
     }
 
     fun undo() {
+        if (mPaths.isEmpty() && mLastPaths.isNotEmpty()) {
+            mPaths = mLastPaths.clone() as LinkedHashMap<MyPath, PaintOptions>
+            mBackgroundBitmap = mLastBackgroundBitmap
+            mLastPaths.clear()
+            pathsUpdated()
+            invalidate()
+            return
+        }
+
         if (mPaths.isEmpty())
             return
 
@@ -182,6 +196,8 @@ class MyCanvas(context: Context, attrs: AttributeSet) : View(context, attrs) {
     }
 
     fun clearCanvas() {
+        mLastPaths = mPaths.clone() as LinkedHashMap<MyPath, PaintOptions>
+        mLastBackgroundBitmap = mBackgroundBitmap
         mBackgroundBitmap = null
         mPath.reset()
         mPaths.clear()
@@ -219,7 +235,7 @@ class MyCanvas(context: Context, attrs: AttributeSet) : View(context, attrs) {
     }
 
     private fun pathsUpdated() {
-        mListener?.pathsChanged(mPaths.size)
+        mListener?.toggleUndoVisibility(mPaths.isNotEmpty() || mLastPaths.isNotEmpty())
     }
 
     override fun onTouchEvent(event: MotionEvent): Boolean {
@@ -240,10 +256,6 @@ class MyCanvas(context: Context, attrs: AttributeSet) : View(context, attrs) {
         return true
     }
 
-    interface PathsChangedListener {
-        fun pathsChanged(cnt: Int)
-    }
-
     public override fun onSaveInstanceState(): Parcelable {
         val superState = super.onSaveInstanceState()
         val savedState = MyParcelable(superState)