TabLayout for NativeScript tabs

src/org/nativescript/widgets/TabStrip.java

@@ -0,0 +1,168 @@
+/*
+ * Copyright 2014 Google Inc. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.nativescript.widgets;
+
+
+import android.content.Context;
+import android.graphics.Canvas;
+import android.graphics.Color;
+import android.graphics.Paint;
+import android.util.AttributeSet;
+import android.util.TypedValue;
+import android.view.View;
+import android.widget.LinearLayout;
+
+class TabStrip extends LinearLayout {
+
+    private static final int DEFAULT_BOTTOM_BORDER_THICKNESS_DIPS = 0;
+    private static final byte DEFAULT_BOTTOM_BORDER_COLOR_ALPHA = 0x26;
+    private static final int SELECTED_INDICATOR_THICKNESS_DIPS = 3;
+    private static final int DEFAULT_SELECTED_INDICATOR_COLOR = 0xFF33B5E5;
+
+    private final int mBottomBorderThickness;
+    private final Paint mBottomBorderPaint;
+
+    private final int mSelectedIndicatorThickness;
+    private final Paint mSelectedIndicatorPaint;
+
+    private final int mDefaultBottomBorderColor;
+
+    private int mSelectedPosition;
+    private float mSelectionOffset;
+
+    private TabLayout.TabColorizer mCustomTabColorizer;
+    private final SimpleTabColorizer mDefaultTabColorizer;
+
+    TabStrip(Context context) {
+        this(context, null);
+    }
+
+    TabStrip(Context context, AttributeSet attrs) {
+        super(context, attrs);
+        setWillNotDraw(false);
+
+        final float density = getResources().getDisplayMetrics().density;
+
+        TypedValue outValue = new TypedValue();
+        context.getTheme().resolveAttribute(android.R.attr.colorForeground, outValue, true);
+        final int themeForegroundColor =  outValue.data;
+
+        mDefaultBottomBorderColor = setColorAlpha(themeForegroundColor,
+                DEFAULT_BOTTOM_BORDER_COLOR_ALPHA);
+
+        mDefaultTabColorizer = new SimpleTabColorizer();
+        mDefaultTabColorizer.setIndicatorColors(DEFAULT_SELECTED_INDICATOR_COLOR);
+
+        mBottomBorderThickness = (int) (DEFAULT_BOTTOM_BORDER_THICKNESS_DIPS * density);
+        mBottomBorderPaint = new Paint();
+        mBottomBorderPaint.setColor(mDefaultBottomBorderColor);
+
+        mSelectedIndicatorThickness = (int) (SELECTED_INDICATOR_THICKNESS_DIPS * density);
+        mSelectedIndicatorPaint = new Paint();
+    }
+
+    void setCustomTabColorizer(TabLayout.TabColorizer customTabColorizer) {
+        mCustomTabColorizer = customTabColorizer;
+        invalidate();
+    }
+
+    void setSelectedIndicatorColors(int... colors) {
+        // Make sure that the custom colorizer is removed
+        mCustomTabColorizer = null;
+        mDefaultTabColorizer.setIndicatorColors(colors);
+        invalidate();
+    }
+
+    void onViewPagerPageChanged(int position, float positionOffset) {
+        mSelectedPosition = position;
+        mSelectionOffset = positionOffset;
+        invalidate();
+    }
+
+    @Override
+    protected void onDraw(Canvas canvas) {
+        final int height = getHeight();
+        final int childCount = getChildCount();
+        final TabLayout.TabColorizer tabColorizer = mCustomTabColorizer != null
+                ? mCustomTabColorizer
+                : mDefaultTabColorizer;
+
+        // Thick colored underline below the current selection
+        if (childCount > 0) {
+            View selectedTitle = getChildAt(mSelectedPosition);
+            int left = selectedTitle.getLeft();
+            int right = selectedTitle.getRight();
+            int color = tabColorizer.getIndicatorColor(mSelectedPosition);
+
+            if (mSelectionOffset > 0f && mSelectedPosition < (getChildCount() - 1)) {
+                int nextColor = tabColorizer.getIndicatorColor(mSelectedPosition + 1);
+                if (color != nextColor) {
+                    color = blendColors(nextColor, color, mSelectionOffset);
+                }
+
+                // Draw the selection partway between the tabs
+                View nextTitle = getChildAt(mSelectedPosition + 1);
+                left = (int) (mSelectionOffset * nextTitle.getLeft() +
+                        (1.0f - mSelectionOffset) * left);
+                right = (int) (mSelectionOffset * nextTitle.getRight() +
+                        (1.0f - mSelectionOffset) * right);
+            }
+
+            mSelectedIndicatorPaint.setColor(color);
+
+            canvas.drawRect(left, height - mSelectedIndicatorThickness, right,
+                    height, mSelectedIndicatorPaint);
+        }
+
+        // Thin underline along the entire bottom edge
+        canvas.drawRect(0, height - mBottomBorderThickness, getWidth(), height, mBottomBorderPaint);
+    }
+
+    /**
+     * Set the alpha value of the {@code color} to be the given {@code alpha} value.
+     */
+    private static int setColorAlpha(int color, byte alpha) {
+        return Color.argb(alpha, Color.red(color), Color.green(color), Color.blue(color));
+    }
+
+    /**
+     * Blend {@code color1} and {@code color2} using the given ratio.
+     *
+     * @param ratio of which to blend. 1.0 will return {@code color1}, 0.5 will give an even blend,
+     *              0.0 will return {@code color2}.
+     */
+    private static int blendColors(int color1, int color2, float ratio) {
+        final float inverseRation = 1f - ratio;
+        float r = (Color.red(color1) * ratio) + (Color.red(color2) * inverseRation);
+        float g = (Color.green(color1) * ratio) + (Color.green(color2) * inverseRation);
+        float b = (Color.blue(color1) * ratio) + (Color.blue(color2) * inverseRation);
+        return Color.rgb((int) r, (int) g, (int) b);
+    }
+
+    private static class SimpleTabColorizer implements TabLayout.TabColorizer {
+        private int[] mIndicatorColors;
+
+        @Override
+        public final int getIndicatorColor(int position) {
+            return mIndicatorColors[position % mIndicatorColors.length];
+        }
+
+        void setIndicatorColors(int... colors) {
+            mIndicatorColors = colors;
+        }
+    }
+}