Add new properties `clearBufferWhenStopped` and `resetFrameIndexWhenStopped`

SDWebImage/Core/SDAnimatedImageView.h

@@ -58,6 +58,20 @@
  */
 @property (nonatomic, assign) BOOL shouldIncrementalLoad;
 
+/**
+ Whether or not to clear the frame buffer cache when animation stopped. See `maxBufferSize`
+ This is useful when you want to limit the memory usage during frequently visibility changes (such as image view inside a list view, then push and pop)
+ Default is NO.
+ */
+@property (nonatomic, assign) BOOL clearBufferWhenStopped;
+
+/**
+ Whether or not to reset the current frame index when animation stopped.
+ For some of use case, you may want to reset the frame index to 0 when stop, but some other want to keep the current frame index.
+ Default is NO.
+ */
+@property (nonatomic, assign) BOOL resetFrameIndexWhenStopped;
+
 #if SD_UIKIT
 /**
  You can specify a runloop mode to let it rendering.

SDWebImage/Core/SDAnimatedImageView.m

@@ -149,21 +149,15 @@ static NSUInteger SDDeviceFreeMemory() {
     self.animatedImage = nil;
     self.totalFrameCount = 0;
     self.totalLoopCount = 0;
-    self.currentFrame = nil;
+    // reset current state
-    self.currentFrameIndex = 0;
+    [self resetCurrentFrameIndex];
-    self.currentLoopCount = 0;
-    self.currentTime = 0;
-    self.bufferMiss = NO;
     self.shouldAnimate = NO;
     self.isProgressive = NO;
     self.maxBufferCount = 0;
     self.animatedImageScale = 1;
     [_fetchQueue cancelAllOperations];
-    _fetchQueue = nil;
+    // clear buffer cache
-    SD_LOCK(self.lock);
+    [self clearFrameBuffer];
-    [_frameBuffer removeAllObjects];
-    _frameBuffer = nil;
-    SD_UNLOCK(self.lock);
 }
 
 - (void)resetProgressiveImage
@@ -179,6 +173,23 @@ static NSUInteger SDDeviceFreeMemory() {
     // preserve buffer cache
 }
 
+- (void)resetCurrentFrameIndex
+{
+    self.currentFrame = nil;
+    self.currentFrameIndex = 0;
+    self.currentLoopCount = 0;
+    self.currentTime = 0;
+    self.bufferMiss = NO;
+}
+
+- (void)clearFrameBuffer
+{
+    SD_LOCK(self.lock);
+    [_frameBuffer removeAllObjects];
+    _frameBuffer = nil;
+    SD_UNLOCK(self.lock);
+}
+
 #pragma mark - Accessors
 #pragma mark Public
 
@@ -466,6 +477,12 @@ static NSUInteger SDDeviceFreeMemory() {
 #else
         _displayLink.paused = YES;
 #endif
+        if (self.resetFrameIndexWhenStopped) {
+            [self resetCurrentFrameIndex];
+        }
+        if (self.clearBufferWhenStopped) {
+            [self clearFrameBuffer];
+        }
     } else {
 #if SD_UIKIT
         [super stopAnimating];