iPhone like PageIndicator for Android

PageIndicator.java

package com.gist.hattorix;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.util.AttributeSet;
import android.view.View;

public class PageIndicator extends View {
    static final String TAG = "PageIndicator";

    /** 総ページ数。 */
    private int pageCount = 0;
    /** 現在のページ。 */
    private int currentPage = 0;
    /** インジケータの半径。 */
    private float indicatorRadius = 5;
    /** インジケータの間隔。 */
    private int indicatorGap = 10;

    public PageIndicator(Context context) {
        this(context, null);
    }

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

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

        pageCount = attrs.getAttributeIntValue(null, "page_count", pageCount);
        indicatorRadius = attrs.getAttributeFloatValue(null,
                "inidicator_diameter", indicatorRadius);
        indicatorGap = attrs.getAttributeIntValue(null, "inidicator_gap",
                indicatorGap);
    }

    // ------------------------------------------------------------------------
    // getter/setter
    // ------------------------------------------------------------------------

    /**
     * @return pageCount
     */
    public int getPageCount() {
        return pageCount;
    }

    /**
     * @param pageCount セットする pageCount
     */
    public void setPageCount(int pageCount) {
        this.pageCount = pageCount;
        if (currentPage >= pageCount) {
            currentPage = pageCount - 1;
        }
        invalidate();
    }

    /**
     * @return currentPage
     */
    public int getCurrentPage() {
        return currentPage;
    }

    /**
     * @param currentPage セットする currentPage
     */
    public void setCurrentPage(int currentPage) {
        this.currentPage = currentPage;
        invalidate();
    }

    /**
     * @return indicatorRadius
     */
    public float getIndicatorRadius() {
        return indicatorRadius;
    }

    /**
     * @param indicatorRadius セットする indicatorRadius
     */
    public void setIndicatorRadius(float indicatorRadius) {
        this.indicatorRadius = indicatorRadius;
        invalidate();
    }

    /**
     * @return indicatorGap
     */
    public int getIndicatorGap() {
        return indicatorGap;
    }

    /**
     * @param indicatorGap セットする indicatorGap
     */
    public void setIndicatorGap(int indicatorGap) {
        this.indicatorGap = indicatorGap;
        invalidate();
    }

    // ------------------------------------------------------------------------
    // Override
    // ------------------------------------------------------------------------

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        int widthMode = MeasureSpec.getMode(widthMeasureSpec);
        int heightMode = MeasureSpec.getMode(heightMeasureSpec);
        int widthSize = MeasureSpec.getSize(widthMeasureSpec);
        int heightSize = MeasureSpec.getSize(heightMeasureSpec);

        int width;
        int height = 0;

        // 幅の計算
        if (widthMode == MeasureSpec.EXACTLY) {
            // Parent has told us how big to be. So be it.
            width = widthSize;
        } else {
            width = getDrawingWidth();
        }

        // 高さの計算
        if (heightMode == MeasureSpec.EXACTLY) {
            // Parent has told us how big to be. So be it.
            height = heightSize;
        } else {
            if (pageCount > 0) {
                height = (int) Math.ceil(indicatorRadius * 2) + getPaddingTop()
                         + getPaddingBottom();
            }
        }

        setMeasuredDimension(width, height);
    }

    @Override
    protected void onDraw(Canvas canvas) {
        // Draw the background for this view
        super.onDraw(canvas);

        if (pageCount == 0) return;

        float cy = (float) getHeight() / 2;
        int width = getWidth();
        int drawingWidth = getDrawingWidth();
        float vspec = (float) (width - drawingWidth) / 2 + indicatorRadius;

        Paint paint = new Paint();
        paint.setColor(Color.WHITE);
        paint.setAntiAlias(true);
        paint.setAlpha(64);

        for (int i = 0; i < pageCount; i++) {
            if (i == currentPage) {
                int alpha = paint.getAlpha();
                paint.setAlpha(255);
                canvas.drawCircle(vspec, cy, indicatorRadius, paint);
                paint.setAlpha(alpha);
            } else {
                canvas.drawCircle(vspec, cy, indicatorRadius, paint);
            }

            vspec += indicatorRadius * 2 + indicatorGap;
        }
    }

    // ------------------------------------------------------------------------
    // private
    // ------------------------------------------------------------------------

    /**
     * 描画幅のサイズを取得します。
     * 
     * @return 描画幅のサイズ
     */
    private int getDrawingWidth() {
        if (pageCount == 0) return 0;

        float width = (pageCount - 1) * indicatorGap;
        width += (pageCount * indicatorRadius * 2);
        return (int) width;
    }
}