Make sure to re-calculate step if not explicitly set

Summary:
This causes the step to be re-calculated on every update of min, max and step value,
to use the most up to date values for the calculation,
except if step is explicitly set to a non-zero value by the user.

Fixes #10253

**Test plan (required)**
1. Create example app
2. Create a view with a slider that has a `value`, `minimumValue` and `maximumValue` set, but no step value (or step value set to 0).

   For example:

   ```
   <Slider
       maximumValue={10}
       minimumValue={1}
       value={4}
       />
   ```
3. See slider working as expected
Closes https://github.com/facebook/react-native/pull/10343

Differential Revision: D4142646

Pulled By: hramos

fbshipit-source-id: a0df87bbdbbd4b2a291d89f5579f73f517a33dfc

ReactAndroid/src/main/java/com/facebook/react/views/slider/ReactSlider.java

@@ -30,7 +30,7 @@ public class ReactSlider extends SeekBar {
   /**
    * If step is 0 (unset) we default to this total number of steps.
    * Don't use 100 which leads to rounding errors (0.200000000001).
-   */ 
+   */
   private static int DEFAULT_TOTAL_STEPS = 128;
 
   /**
@@ -50,6 +50,7 @@ public class ReactSlider extends SeekBar {
    * If zero it's determined automatically.
    */
   private double mStep = 0;
+  private double mStepCalculated = 0;
 
   public ReactSlider(Context context, @Nullable AttributeSet attrs, int style) {
     super(context, attrs, style);
@@ -83,7 +84,7 @@ public class ReactSlider extends SeekBar {
     if (seekBarProgress == getMax()) {
       return mMaxValue;
     }
-    return seekBarProgress * mStep + mMinValue;
+    return seekBarProgress * getStepValue() + mMinValue;
   }
 
   /**
@@ -91,7 +92,7 @@ public class ReactSlider extends SeekBar {
    */
   private void updateAll() {
     if (mStep == 0) {
-      mStep = (mMaxValue - mMinValue) / (double) DEFAULT_TOTAL_STEPS;
+      mStepCalculated = (mMaxValue - mMinValue) / (double) DEFAULT_TOTAL_STEPS;
     }
     setMax(getTotalSteps());
     updateValue();
@@ -106,6 +107,10 @@ public class ReactSlider extends SeekBar {
   }
 
   private int getTotalSteps() {
-    return (int) Math.ceil((mMaxValue - mMinValue) / mStep);
+    return (int) Math.ceil((mMaxValue - mMinValue) / getStepValue());
+  }
+
+  private double getStepValue() {
+    return mStep > 0 ? mStep : mStepCalculated;
   }
 }

ReactAndroid/src/test/java/com/facebook/react/views/BUCK

@@ -24,6 +24,7 @@ robolectric3_test(
     react_native_target('java/com/facebook/react/uimanager/annotations:annotations'),
     react_native_target('java/com/facebook/react/uimanager:uimanager'),
     react_native_target('java/com/facebook/react/views/image:image'),
+    react_native_target('java/com/facebook/react/views/slider:slider'),
     react_native_target('java/com/facebook/react/views/text:text'),
     react_native_target('java/com/facebook/react/views/textinput:textinput'),
     react_native_target('java/com/facebook/react/views/view:view'),

ReactAndroid/src/test/java/com/facebook/react/views/slider/ReactSliderPropertyTest.java

@@ -0,0 +1,105 @@
+/**
+ * Copyright (c) 2015-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ */
+
+package com.facebook.react.views.slider;
+
+import android.widget.SeekBar;
+import com.facebook.react.bridge.CatalystInstance;
+import com.facebook.react.bridge.JavaOnlyMap;
+import com.facebook.react.bridge.ReactApplicationContext;
+import com.facebook.react.bridge.ReactTestHelper;
+import com.facebook.react.uimanager.ReactStylesDiffMap;
+import com.facebook.react.uimanager.ThemedReactContext;
+import org.junit.Before;
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.powermock.core.classloader.annotations.PowerMockIgnore;
+import org.powermock.modules.junit4.rule.PowerMockRule;
+import org.robolectric.RobolectricTestRunner;
+import org.robolectric.RuntimeEnvironment;
+
+import static org.fest.assertions.api.Assertions.assertThat;
+
+/**
+ * Verify {@link SeekBar} view property being applied properly by {@link ReactSliderManager}
+ */
+@RunWith(RobolectricTestRunner.class)
+@PowerMockIgnore({"org.mockito.*", "org.robolectric.*", "android.*"})
+public class ReactSliderPropertyTest {
+
+  @Rule
+  public PowerMockRule rule = new PowerMockRule();
+
+  private ThemedReactContext mThemedContext;
+  private ReactSliderManager mManager;
+
+  @Before
+  public void setup() {
+    ReactApplicationContext mContext = new ReactApplicationContext(RuntimeEnvironment.application);
+    CatalystInstance mCatalystInstanceMock = ReactTestHelper.createMockCatalystInstance();
+    mContext.initializeWithInstance(mCatalystInstanceMock);
+    mThemedContext = new ThemedReactContext(mContext, mContext);
+    mManager = new ReactSliderManager();
+  }
+
+  public ReactStylesDiffMap buildStyles(Object... keysAndValues) {
+    return new ReactStylesDiffMap(JavaOnlyMap.of(keysAndValues));
+  }
+
+  @Test
+  public void testValueWithMaxValue() {
+    ReactSlider view = mManager.createViewInstance(mThemedContext);
+
+    mManager.updateProperties(view, buildStyles("maximumValue", 10.0));
+    mManager.updateProperties(view, buildStyles("value", 5.5));
+    assertThat(view.getProgress()).isEqualTo(70);
+  }
+
+  @Test
+  public void testValueWithMaxValueSetBeforeMinValue() {
+    ReactSlider view = mManager.createViewInstance(mThemedContext);
+
+    mManager.updateProperties(view, buildStyles("maximumValue", 10.0));
+    mManager.updateProperties(view, buildStyles("minimumValue", 5.0));
+    mManager.updateProperties(view, buildStyles("value", 5.5));
+    assertThat(view.getProgress()).isEqualTo(13);
+  }
+
+  @Test
+  public void testValueWithMinValueSetBeforeMaxValue() {
+    ReactSlider view = mManager.createViewInstance(mThemedContext);
+
+    mManager.updateProperties(view, buildStyles("minimumValue", 5.0));
+    mManager.updateProperties(view, buildStyles("maximumValue", 10.0));
+    mManager.updateProperties(view, buildStyles("value", 5.5));
+    assertThat(view.getProgress()).isEqualTo(13);
+  }
+
+  @Test
+  public void testValueWithMaxValueAndStep() {
+    ReactSlider view = mManager.createViewInstance(mThemedContext);
+
+    mManager.updateProperties(view, buildStyles("maximumValue", 10.0));
+    mManager.updateProperties(view, buildStyles("step", 3.0));
+    mManager.updateProperties(view, buildStyles("value", 5.5));
+    assertThat(view.getProgress()).isEqualTo(2);
+  }
+
+  @Test
+  public void testValueWithMaxValueAndMinValueAndStep() {
+    ReactSlider view = mManager.createViewInstance(mThemedContext);
+
+    mManager.updateProperties(view, buildStyles("maximumValue", 10.0));
+    mManager.updateProperties(view, buildStyles("minimumValue", 5.0));
+    mManager.updateProperties(view, buildStyles("step", 3.0));
+    mManager.updateProperties(view, buildStyles("value", 10.0));
+    assertThat(view.getProgress()).isEqualTo(2);
+  }
+}