java source code of TabStrip

/*
 * Copyright (C) 2013 Andreas Stuetz <[email protected]>, modified by John Persano 2015
 *
 * 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 uk.org.crimetalk.views;

import android.annotation.SuppressLint;
import android.content.Context;
import android.content.res.TypedArray;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.graphics.Paint.Style;
import android.graphics.Typeface;
import android.os.Build;
import android.os.Parcel;
import android.os.Parcelable;
import android.support.annotation.NonNull;
import android.support.v4.view.ViewPager;
import android.support.v4.view.ViewPager.OnPageChangeListener;
import android.util.AttributeSet;
import android.util.DisplayMetrics;
import android.util.TypedValue;
import android.view.Gravity;
import android.view.View;
import android.view.ViewTreeObserver.OnGlobalLayoutListener;
import android.widget.HorizontalScrollView;
import android.widget.ImageButton;
import android.widget.LinearLayout;
import android.widget.TextView;

import java.util.Locale;

import uk.org.crimetalk.R;


public class TabStrip extends HorizontalScrollView {

    public interface IconTabProvider {
        public int getPageIconResId(int position);
    }

    // @formatter:off
    private static final int[] ATTRS = new int[] {
            android.R.attr.textSize,
            android.R.attr.textColor
    };
    // @formatter:on

    private final LinearLayout.LayoutParams defaultTabLayoutParams;
    private final LinearLayout.LayoutParams expandedTabLayoutParams;

    private final PageListener pageListener = new PageListener();
    private OnPageChangeListener delegatePageListener;

    private final LinearLayout tabsContainer;
    private ViewPager pager;

    private int tabCount;

    private int currentPosition = 0;
    private float currentPositionOffset = 0f;

    private final Paint rectPaint;

    private int indicatorColor = 0xFFFFFFFF;
    private int underlineColor = 0x1A000000;

    private boolean shouldExpand = false;

    private int scrollOffset = 52;
    private int indicatorHeight = 8;
    private int underlineHeight = 2;
    private int tabPadding = 24;
    private int indicatorPadding = 0;

    private int tabTextSize = 14;
    private int tabTextColor = 0xFF666666;
    private int tabDeactivateTextColor = 0xFF00CCCC;

    private final Typeface tabTypeface = null;

    private int lastScrollX = 0;

    private int tabBackgroundResId = R.drawable.selector_tab;

    private Locale locale;

    private boolean tabSwitch;

    public TabStrip(Context context, AttributeSet attrs) {
        this(context, attrs, 0);
    }

    public TabStrip(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);

        setFillViewport(true);
        setWillNotDraw(false);

        tabsContainer = new LinearLayout(context);
        tabsContainer.setOrientation(LinearLayout.HORIZONTAL);
        tabsContainer.setLayoutParams(new LayoutParams(LayoutParams.MATCH_PARENT, LayoutParams.MATCH_PARENT));
        addView(tabsContainer);

        DisplayMetrics dm = getResources().getDisplayMetrics();

        scrollOffset = (int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, scrollOffset, dm);
        indicatorHeight = (int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, indicatorHeight, dm);
        underlineHeight = (int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, underlineHeight, dm);
        tabPadding = (int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, tabPadding, dm);
        tabTextSize = (int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_SP, tabTextSize, dm);
        indicatorPadding = (int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_SP, indicatorPadding, dm);

        // get system attrs (android:textSize and android:textColor)

        TypedArray a = context.obtainStyledAttributes(attrs, ATTRS);

        tabTextSize = a.getDimensionPixelSize(0, tabTextSize);

        a.recycle();

        a = context.obtainStyledAttributes(attrs, R.styleable.TabStrip);

        indicatorColor = a.getColor(R.styleable.TabStrip_pstsIndicatorColor, indicatorColor);
        underlineColor = a.getColor(R.styleable.TabStrip_pstsUnderlineColor, underlineColor);
        indicatorHeight = a.getDimensionPixelSize(R.styleable.TabStrip_pstsIndicatorHeight, indicatorHeight);
        underlineHeight = a.getDimensionPixelSize(R.styleable.TabStrip_pstsUnderlineHeight, underlineHeight);
        tabPadding = a.getDimensionPixelSize(R.styleable.TabStrip_pstsTabPaddingLeftRight, tabPadding);
        tabBackgroundResId = a.getResourceId(R.styleable.TabStrip_pstsTabBackground, tabBackgroundResId);
        shouldExpand = a.getBoolean(R.styleable.TabStrip_pstsShouldExpand, shouldExpand);
        scrollOffset = a.getDimensionPixelSize(R.styleable.TabStrip_pstsScrollOffset, scrollOffset);
        tabSwitch = a.getBoolean(R.styleable.TabStrip_pstsTabSwitch, tabSwitch);
        tabTextColor = a.getColor(R.styleable.TabStrip_pstsActivateTextColor, tabTextColor);
        tabDeactivateTextColor = a.getColor(R.styleable.TabStrip_pstsDeactivateTextColor, tabDeactivateTextColor);
        indicatorPadding = a.getDimensionPixelSize(R.styleable.TabStrip_pstsIndicatorPadding, indicatorPadding);

        a.recycle();

        rectPaint = new Paint();
        rectPaint.setAntiAlias(true);
        rectPaint.setStyle(Style.FILL);

        defaultTabLayoutParams = new LinearLayout.LayoutParams(LayoutParams.WRAP_CONTENT, LayoutParams.MATCH_PARENT);
        expandedTabLayoutParams = new LinearLayout.LayoutParams(0, LayoutParams.MATCH_PARENT, 1.0f);

        if (locale == null) {
            locale = getResources().getConfiguration().locale;
        }
    }

    public void setViewPager(ViewPager pager) {
        this.pager = pager;

        if (pager.getAdapter() == null) {
            throw new IllegalStateException("ViewPager does not have adapter instance.");
        }

        pager.setOnPageChangeListener(pageListener);

        notifyDataSetChanged();
    }

    @SuppressWarnings("UnusedDeclaration")
    public void setOnPageChangeListener(OnPageChangeListener listener) {
        this.delegatePageListener = listener;
    }

    void notifyDataSetChanged() {

        tabsContainer.removeAllViews();

        tabCount = pager.getAdapter().getCount();

        for (int i = 0; i < tabCount; i++) {

            if (pager.getAdapter() instanceof IconTabProvider) {
                addIconTab(i, ((IconTabProvider) pager.getAdapter()).getPageIconResId(i));
            } else {
                addTextTab(i, pager.getAdapter().getPageTitle(i).toString());
            }

        }

        updateTabStyles();

        getViewTreeObserver().addOnGlobalLayoutListener(new OnGlobalLayoutListener() {

            @SuppressWarnings("deprecation")
            @SuppressLint("NewApi")
            @Override
            public void onGlobalLayout() {

                if (Build.VERSION.SDK_INT < Build.VERSION_CODES.JELLY_BEAN) {
                    getViewTreeObserver().removeGlobalOnLayoutListener(this);
                } else {
                    getViewTreeObserver().removeOnGlobalLayoutListener(this);
                }

                currentPosition = pager.getCurrentItem();
                scrollToChild(currentPosition, 0);
            }
        });
    }

    private void addTextTab(final int position, String title) {

        TextView tab = new TextView(getContext());
        tab.setText(title);
        tab.setGravity(Gravity.CENTER);
        tab.setSingleLine();
        tab.setAllCaps(true);

        addTab(position, tab);
    }

    private void addIconTab(final int position, int resId) {

        ImageButton tab = new ImageButton(getContext());
        tab.setImageResource(resId);

        addTab(position, tab);
    }

    private void addTab(final int position, View tab) {
        tab.setFocusable(true);
        tab.setOnClickListener(new OnClickListener() {
            @Override
            public void onClick(View v) {
                pager.setCurrentItem(position);
            }
        });

        tab.setPadding(tabPadding, 0, tabPadding, 0);

        tabsContainer.addView(tab, position, shouldExpand ? expandedTabLayoutParams : defaultTabLayoutParams);
    }

    private void updateTabStyles() {

        for (int i = 0; i < tabCount; i++) {

            View v = tabsContainer.getChildAt(i);

            v.setBackgroundResource(tabBackgroundResId);

            if (v instanceof TextView) {

                TextView tab = (TextView) v;
                tab.setTextSize(TypedValue.COMPLEX_UNIT_PX, tabTextSize);
                int tabTypefaceStyle = Typeface.BOLD;
                tab.setTypeface(tabTypeface, tabTypefaceStyle);
                tab.setTextColor(i == currentPosition ? tabTextColor : tabDeactivateTextColor);

            }

        }

    }

    private void updateActivateTab(final int position) {

        for (int i = 0; i < tabCount; i++) {

            View v = tabsContainer.getChildAt(i);

            if (v instanceof TextView) {
                TextView tab = (TextView) v;
                tab.setTextColor(position == i ? tabTextColor : tabDeactivateTextColor);
            } else {
                v.setSelected(position == i);
            }
        }
    }

    private void scrollToChild(int position, int offset) {

        if (tabCount == 0) {
            return;
        }

        int newScrollX = tabsContainer.getChildAt(position).getLeft() + offset;

        if (position > 0 || offset > 0) {
            newScrollX -= scrollOffset;
        }

        if (newScrollX != lastScrollX) {
            lastScrollX = newScrollX;
            scrollTo(newScrollX, 0);
        }

    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);

        if (isInEditMode() || tabCount == 0) {
            return;
        }

        final int height = getHeight();

        // draw indicator line

        rectPaint.setColor(indicatorColor);

        // default: line below current tab
        View currentTab = tabsContainer.getChildAt(currentPosition);

        float lineLeft = currentTab.getLeft();
        lineLeft += indicatorPadding;

        float lineRight = currentTab.getRight();
        lineRight -= indicatorPadding;

        // if there is an offset, start interpolating left and right coordinates between current and next tab
        if (currentPositionOffset > 0f && currentPosition < tabCount - 1) {

            View nextTab = tabsContainer.getChildAt(currentPosition + 1);
            float nextTabLeft = nextTab.getLeft();
            nextTabLeft += indicatorPadding;

            float nextTabRight = nextTab.getRight();
            nextTabRight -= indicatorPadding;

            lineLeft = (currentPositionOffset * nextTabLeft + (1f - currentPositionOffset) * lineLeft);
            lineRight = (currentPositionOffset * nextTabRight + (1f - currentPositionOffset) * lineRight);

        }

        canvas.drawRect(lineLeft, height - indicatorHeight, lineRight, height - underlineHeight, rectPaint);

        // draw underline

        rectPaint.setColor(underlineColor);
        canvas.drawRect(0, height - underlineHeight, tabsContainer.getWidth(), height, rectPaint);

    }

    private class PageListener implements OnPageChangeListener {

        @Override
        public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {

            currentPosition = position;
            currentPositionOffset = positionOffset;

            scrollToChild(position, (int) (positionOffset * tabsContainer.getChildAt(position).getWidth()));

            invalidate();

            if (delegatePageListener != null) {
                delegatePageListener.onPageScrolled(position, positionOffset, positionOffsetPixels);
            }
        }

        @Override
        public void onPageScrollStateChanged(int state) {
            if (state == ViewPager.SCROLL_STATE_IDLE) {
                scrollToChild(pager.getCurrentItem(), 0);
            }

            if (delegatePageListener != null) {
                delegatePageListener.onPageScrollStateChanged(state);
            }
        }

        @Override
        public void onPageSelected(int position) {

            updateActivateTab(position);

            if (delegatePageListener != null) {
                delegatePageListener.onPageSelected(position);
            }
        }

    }

    @Override
    public void onRestoreInstanceState(Parcelable state) {
        SavedState savedState = (SavedState) state;
        super.onRestoreInstanceState(savedState.getSuperState());
        currentPosition = savedState.currentPosition;
        requestLayout();
    }

    @Override
    public Parcelable onSaveInstanceState() {
        Parcelable superState = super.onSaveInstanceState();
        SavedState savedState = new SavedState(superState);
        savedState.currentPosition = currentPosition;
        return savedState;
    }

    static class SavedState extends BaseSavedState {
        int currentPosition;

        public SavedState(Parcelable superState) {
            super(superState);
        }

        private SavedState(Parcel in) {
            super(in);
            currentPosition = in.readInt();
        }

        @Override
        public void writeToParcel(@NonNull Parcel dest, int flags) {
            super.writeToParcel(dest, flags);
            dest.writeInt(currentPosition);
        }

        public static final Parcelable.Creator<SavedState> CREATOR = new Parcelable.Creator<SavedState>() {
            @Override
            public SavedState createFromParcel(Parcel in) {
                return new SavedState(in);
            }

            @Override
            public SavedState[] newArray(int size) {
                return new SavedState[size];
            }
        };
    }

}