Prevent reflection - ScaleGestureDetector#mMinSpan

Also makes "minScalingSpan" accessible to developers
via ViewConfiguration in case developers were accessing
mMinSpan in order to simply read the value of the field,
since that was previously the only way to read the value.

Fixes: 123768938
Test: android.view.cts.ViewConfigurationTest

Change-Id: Ib179aa153f00a55b6913c7497a1e43bd101f41d3

api/current.txt

@@ -51111,6 +51111,7 @@ package android.view {
     method public int getScaledHoverSlop();
     method public int getScaledMaximumDrawingCacheSize();
     method public int getScaledMaximumFlingVelocity();
+    method public int getScaledMinScalingSpan();
     method public int getScaledMinimumFlingVelocity();
     method public int getScaledOverflingDistance();
     method public int getScaledOverscrollDistance();

core/java/android/view/ScaleGestureDetector.java

@@ -18,7 +18,6 @@ package android.view;
 
 import android.annotation.UnsupportedAppUsage;
 import android.content.Context;
-import android.content.res.Resources;
 import android.os.Build;
 import android.os.Handler;
 
@@ -145,7 +144,7 @@ public class ScaleGestureDetector {
     private boolean mInProgress;
     @UnsupportedAppUsage(maxTargetSdk = Build.VERSION_CODES.P, trackingBug = 123768938)
     private int mSpanSlop;
-    @UnsupportedAppUsage
+    @UnsupportedAppUsage(maxTargetSdk = Build.VERSION_CODES.P, trackingBug = 123768938)
     private int mMinSpan;
 
     private final Handler mHandler;
@@ -200,10 +199,9 @@ public class ScaleGestureDetector {
                                 Handler handler) {
         mContext = context;
         mListener = listener;
-        mSpanSlop = ViewConfiguration.get(context).getScaledTouchSlop() * 2;
-
-        final Resources res = context.getResources();
-        mMinSpan = res.getDimensionPixelSize(com.android.internal.R.dimen.config_minScalingSpan);
+        final ViewConfiguration viewConfiguration = ViewConfiguration.get(context);
+        mSpanSlop = viewConfiguration.getScaledTouchSlop() * 2;
+        mMinSpan = viewConfiguration.getScaledMinScalingSpan();
         mHandler = handler;
         // Quick scale is enabled by default after JB_MR2
         final int targetSdkVersion = context.getApplicationInfo().targetSdkVersion;

core/java/android/view/ViewConfiguration.java

@@ -293,12 +293,14 @@ public class ViewConfiguration {
      */
     private static final float AMBIGUOUS_GESTURE_MULTIPLIER = 2f;
 
+    private final boolean mConstructedWithContext;
     private final int mEdgeSlop;
     private final int mFadingEdgeLength;
     private final int mMinimumFlingVelocity;
     private final int mMaximumFlingVelocity;
     private final int mScrollbarSize;
     private final int mTouchSlop;
+    private final int mMinScalingSpan;
     private final int mHoverSlop;
     private final int mMinScrollbarTouchTarget;
     private final int mDoubleTapTouchSlop;
@@ -329,6 +331,7 @@ public class ViewConfiguration {
      */
     @Deprecated
     public ViewConfiguration() {
+        mConstructedWithContext = false;
         mEdgeSlop = EDGE_SLOP;
         mFadingEdgeLength = FADING_EDGE_LENGTH;
         mMinimumFlingVelocity = MINIMUM_FLING_VELOCITY;
@@ -350,6 +353,10 @@ public class ViewConfiguration {
         mHorizontalScrollFactor = HORIZONTAL_SCROLL_FACTOR;
         mVerticalScrollFactor = VERTICAL_SCROLL_FACTOR;
         mShowMenuShortcutsWhenKeyboardPresent = false;
+
+        // Getter throws if mConstructedWithContext is false so doesn't matter what
+        // this value is.
+        mMinScalingSpan = 0;
     }
 
     /**
@@ -363,6 +370,7 @@ public class ViewConfiguration {
      * @see android.util.DisplayMetrics
      */
     private ViewConfiguration(Context context) {
+        mConstructedWithContext = true;
         final Resources res = context.getResources();
         final DisplayMetrics metrics = res.getDisplayMetrics();
         final Configuration config = res.getConfiguration();
@@ -447,6 +455,8 @@ public class ViewConfiguration {
         mShowMenuShortcutsWhenKeyboardPresent = res.getBoolean(
             com.android.internal.R.bool.config_showMenuShortcutsWhenKeyboardPresent);
 
+        mMinScalingSpan = res.getDimensionPixelSize(
+                com.android.internal.R.dimen.config_minScalingSpan);
     }
 
     /**
@@ -958,6 +968,26 @@ public class ViewConfiguration {
         return mShowMenuShortcutsWhenKeyboardPresent;
     }
 
+    /**
+     * Retrieves the distance in pixels between touches that must be reached for a gesture to be
+     * interpreted as scaling.
+     *
+     * In general, scaling shouldn't start until this distance has been met or surpassed, and
+     * scaling should end when the distance in pixels between touches drops below this distance.
+     *
+     * @return The distance in pixels
+     * @throws IllegalStateException if this method is called on a ViewConfiguration that was
+     *         instantiated using a constructor with no Context parameter.
+     */
+    public int getScaledMinScalingSpan() {
+        if (!mConstructedWithContext) {
+            throw new IllegalStateException("Min scaling span cannot be determined when this "
+                    + "method is called on a ViewConfiguration that was instantiated using a "
+                    + "constructor with no Context parameter");
+        }
+        return mMinScalingSpan;
+    }
+
     /**
      * @hide
      * @return Whether or not marquee should use fading edges.