Android 顏色選擇器之ColorPickerDialog剖析

      有這樣一個需求，可以讓使用者自定義背景顏色，這就需要提供一個顏色選擇器給使用者.

      在Android 中，如何實現這樣的功能呢，遇到這種需求是,先檢視一下ApiDemos,是否已經有相關的例項,果然，找到了一個可以參考的demo:ColorPickerDialog

我已經把apidemos匯入到eclipse中,請看截圖:

我們要找的就是這個ColorPickerDialog,在com.example.android.apis.graphics目錄下,是一個顏色選擇器對話方塊，在哪個demo中使用的呢,References下之後，發現是在

FingerPaint，也就是塗鴉的例子中:

接下來還是直接看程式碼:

package com.example.android.apis.graphics;

import android.os.Bundle;
import android.app.Dialog;
import android.content.Context;
import android.graphics.*;
import android.view.MotionEvent;
import android.view.View;

public class ColorPickerDialog extends Dialog {

    public interface OnColorChangedListener {
        void colorChanged(int color);
    }

    private OnColorChangedListener mListener;
    private int mInitialColor;

    private static class ColorPickerView extends View {//顏色選擇器自定義View
        private Paint mPaint;//漸變色環畫筆
 

        private Paint mCenterPaint;//中間圓畫筆
        private final int[] mColors;//漸變色環顏色
        private OnColorChangedListener mListener;//顏色改變回調
        
        ColorPickerView(Context c, OnColorChangedListener l, int color) {
            super(c);
            mListener = l;
            mColors = new int[] {//漸變色陣列
                0xFFFF0000, 0xFFFF00FF, 0xFF0000FF, 0xFF00FFFF, 0xFF00FF00,
                0xFFFFFF00, 0xFFFF0000
            };
            Shader s = new SweepGradient(0, 0, mColors, null);
            //初始化漸變色畫筆
            mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
            mPaint.setShader(s);
            mPaint.setStyle(Paint.Style.STROKE);
            mPaint.setStrokeWidth(32);
            
            //初始化中心園畫筆
            mCenterPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
            mCenterPaint.setColor(color);
            mCenterPaint.setStrokeWidth(5);
        }
        
        private boolean mTrackingCenter;
        private boolean mHighlightCenter;

        @Override 
        protected void onDraw(Canvas canvas) {
            float r = CENTER_X - mPaint.getStrokeWidth()*0.5f;
            
            //移動中心
            canvas.translate(CENTER_X, CENTER_X);
            //畫出色環和中心園
            canvas.drawOval(new RectF(-r, -r, r, r), mPaint);            
            canvas.drawCircle(0, 0, CENTER_RADIUS, mCenterPaint);
            
            if (mTrackingCenter) {
                int c = mCenterPaint.getColor();
                mCenterPaint.setStyle(Paint.Style.STROKE);
                
                if (mHighlightCenter) {
                    mCenterPaint.setAlpha(0xFF);
                } else {
                    mCenterPaint.setAlpha(0x80);
                }
                canvas.drawCircle(0, 0,
                                  CENTER_RADIUS + mCenterPaint.getStrokeWidth(),
                                  mCenterPaint);
                
                mCenterPaint.setStyle(Paint.Style.FILL);
                mCenterPaint.setColor(c);
            }
        }
        
        @Override
        protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
            setMeasuredDimension(CENTER_X*2, CENTER_Y*2);
        }
        
        private static final int CENTER_X = 100;
        private static final int CENTER_Y = 100;
        private static final int CENTER_RADIUS = 32;

        private int floatToByte(float x) {
            int n = java.lang.Math.round(x);
            return n;
        }
        private int pinToByte(int n) {
            if (n < 0) {
                n = 0;
            } else if (n > 255) {
                n = 255;
            }
            return n;
        }
        
        private int ave(int s, int d, float p) {
            return s + java.lang.Math.round(p * (d - s));
        }
        
        private int interpColor(int colors[], float unit) {
            if (unit <= 0) {
                return colors[0];
            }
            if (unit >= 1) {
                return colors[colors.length - 1];
            }
            
            float p = unit * (colors.length - 1);
            int i = (int)p;
            p -= i;

            // now p is just the fractional part [0...1) and i is the index
            int c0 = colors[i];
            int c1 = colors[i+1];
            int a = ave(Color.alpha(c0), Color.alpha(c1), p);
            int r = ave(Color.red(c0), Color.red(c1), p);
            int g = ave(Color.green(c0), Color.green(c1), p);
            int b = ave(Color.blue(c0), Color.blue(c1), p);
            
            return Color.argb(a, r, g, b);
        }
        
        private int rotateColor(int color, float rad) {
            float deg = rad * 180 / 3.1415927f;
            int r = Color.red(color);
            int g = Color.green(color);
            int b = Color.blue(color);
            
            ColorMatrix cm = new ColorMatrix();
            ColorMatrix tmp = new ColorMatrix();

            cm.setRGB2YUV();
            tmp.setRotate(0, deg);
            cm.postConcat(tmp);
            tmp.setYUV2RGB();
            cm.postConcat(tmp);
            
            final float[] a = cm.getArray();

            int ir = floatToByte(a[0] * r +  a[1] * g +  a[2] * b);
            int ig = floatToByte(a[5] * r +  a[6] * g +  a[7] * b);
            int ib = floatToByte(a[10] * r + a[11] * g + a[12] * b);
            
            return Color.argb(Color.alpha(color), pinToByte(ir),
                              pinToByte(ig), pinToByte(ib));
        }
        
        private static final float PI = 3.1415926f;

        @Override
        public boolean onTouchEvent(MotionEvent event) {
            float x = event.getX() - CENTER_X;
            float y = event.getY() - CENTER_Y;
            boolean inCenter = java.lang.Math.sqrt(x*x + y*y) <= CENTER_RADIUS;
            
            switch (event.getAction()) {
                case MotionEvent.ACTION_DOWN:
                    mTrackingCenter = inCenter;
                    if (inCenter) {//是否則中心園
                        mHighlightCenter = true;
                        invalidate();
                        break;
                    }
                case MotionEvent.ACTION_MOVE:
                    if (mTrackingCenter) {
                        if (mHighlightCenter != inCenter) {
                            mHighlightCenter = inCenter;
                            invalidate();
                        }
                    } else {
                        float angle = (float)java.lang.Math.atan2(y, x);
                        // need to turn angle [-PI ... PI] into unit [0....1]
                        float unit = angle/(2*PI);
                        if (unit < 0) {
                            unit += 1;
                        }
                        mCenterPaint.setColor(interpColor(mColors, unit));
                        invalidate();
                    }
                    break;
                case MotionEvent.ACTION_UP:
                    if (mTrackingCenter) {
                        if (inCenter) {
                            mListener.colorChanged(mCenterPaint.getColor());
                        }
                        mTrackingCenter = false;    // so we draw w/o halo
                        invalidate();
                    }
                    break;
            }
            return true;
        }
    }

    public ColorPickerDialog(Context context,
                             OnColorChangedListener listener,
                             int initialColor) {
        super(context);
        
        mListener = listener;
        mInitialColor = initialColor;
    }

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        OnColorChangedListener l = new OnColorChangedListener() {
            public void colorChanged(int color) {
                mListener.colorChanged(color);
                dismiss();
            }
        };

        setContentView(new ColorPickerView(getContext(), l, mInitialColor));
        setTitle("Pick a Color");
    }
}
 

        當然，目前的這個例子還有一定的侷限，比如無黑白色,只能選擇大概的顏色區間(後續會講解). 當然只要把這個demo研究好後，具體的改進不是問題.