策略模式：再见if-else

在软件开发中，我们时常用到if-else来对进行条件判断，然后再进行相应的操作，但这样做会使得项目再日后的维护中出现困难，所以，当遇到比较复杂的if-else结构的时候，使用策略模式是很好的选择

举一个简单的计算小例子，如对两个数进行加减乘除

第一步，定义计算接口

public interface CalculateStrategy {
int calculateComeout(int number1, int number2);
}

第二步，实现策略类

加法策略

public class PlusStrategy implements CalculateStrategy {
@Override
public int calculateComeout(int number1, int number2) {
return number1 + number2;
}
}

减法策略

public class MinusStrategy implements CalculateStrategy {
@Override
public int calculateComeout(int number1, int number2) {
return number1 - number2;
}
}

实例运行

public class Main {
public static void main(String[] args) {
int number1 = 20, number2 = 10;
new PlusStrategy().calculateComeout(number1, number2);
new MinusStrategy().calculateComeout(number1,number2);
}
}

当然，这只是一个十分简单的实例，再实际应用中远没有这么“鸡肋”，比如我曾经开发过的一个小项目

策略模式实战

OpeningStartAnimation是一个开屏动画View，所以这里的策略模式是与绘画策略相关的

绘画策略接口

public interface DrawStrategy {

/**
* 绘制app名称文字
* @param canvas 画布
* @param fraction 完成时间百分比
* @param colorOfAppName 字体颜色
* @param name 文字
* @param widthAndHeightOfView view的宽和高
*/
void drawAppName(Canvas canvas, float fraction, String name, int colorOfAppName,
WidthAndHeightOfView widthAndHeightOfView);

/**
* 绘制app图标
* @param canvas 画布
* @param fraction 完成时间百分比
* @param colorOfIcon 绘制图标颜色
* @param icon 图标
* @param widthAndHeightOfView view的宽和高
*/
void drawAppIcon(Canvas canvas, float fraction, Drawable icon, int colorOfIcon,
WidthAndHeightOfView widthAndHeightOfView);

/**
* 绘制app一句话描述
* @param canvas 画布
* @param fraction 完成时间百分比
* @param statement 一句话描述
* @param colorOfStatement 字体颜色
* @param widthAndHeightOfView view的宽和高
*/
void drawAppStatement(Canvas canvas, float fraction, String statement, int colorOfStatement,
WidthAndHeightOfView widthAndHeightOfView);
}

其中的一个具体实现

public class LineDrawStrategy implements DrawStrategy {

public LineDrawStrategy(){
}

@Override
public void drawAppName(Canvas canvas, float fraction, String name, int colorOfAppName,
WidthAndHeightOfView widthAndHeightOfView) {
canvas.save();
Paint paint = new Paint(Paint.ANTI_ALIAS_FLAG);
paint.setColor(colorOfAppName);
paint.setStyle(Paint.Style.STROKE);
paint.setStrokeWidth(5);
paint.setTextSize(50);
paint.setStrokeJoin(Paint.Join.ROUND);
paint.setTextAlign(Paint.Align.LEFT);
float x = widthAndHeightOfView.getWidth() / 2;
int centerY = widthAndHeightOfView.getHeight() / 2;
float y = centerY - 275;
Path path = new Path();
path.moveTo(x, y);
if (fraction <= 0.50) {
path.lineTo(x, y + (25 + name.length() + 250) * (fraction / 0.50f));
canvas.drawPath(path, paint);
} else {
path.lineTo(x, y + (25 + name.length() + 250) * ((1 - fraction)/ 0.50f));
canvas.drawPath(path, paint);
paint.setStyle(Paint.Style.FILL);
canvas.drawText(name, x + 20, y + 150, paint);
}
canvas.restore();
}

@Override
public void drawAppIcon(Canvas canvas, float fraction, Drawable icon, int colorOfIcon,
WidthAndHeightOfView widthAndHeightOfView) {
int centerX = widthAndHeightOfView.getWidth() / 2;
int centerY = widthAndHeightOfView.getHeight() / 2;
Bitmap bitmap = ((BitmapDrawable) icon).getBitmap();
Paint paint = new Paint(Paint.ANTI_ALIAS_FLAG);
paint.setColor(colorOfIcon);
paint.setStrokeWidth(3);
paint.setStrokeJoin(Paint.Join.ROUND);
paint.setStyle(Paint.Style.STROKE);
float bitmapLeft = centerX - 250;
float bitmapRight = bitmapLeft + bitmap.getWidth() * 1.7f;
float bitmapTop = centerY - 250;
float bitmapBottom = bitmapTop + bitmap.getHeight() * 1.7f;
canvas.save();
if (fraction <= 0.75) {
float newfraction = fraction / 0.75f;
if (newfraction <= 0.25) {
canvas.drawLine(bitmapLeft, bitmapBottom, bitmapLeft,
bitmapBottom - (bitmapBottom - bitmapTop) * (newfraction / 0.25f), paint);
//  path.lineTo(bitmapLeft, bitmapBottom + (bitmapBottom - bitmapTop) * (newfraction / 0.25f));
} else {
canvas.drawLine(bitmapLeft, bitmapBottom, bitmapLeft, bitmapTop, paint);
//  path.lineTo(bitmapLeft, bitmapTop);
}
if (newfraction > 0.25) {
if (newfraction <= 0.50) {
canvas.drawLine(bitmapLeft, bitmapTop,
bitmapLeft + (bitmapRight - bitmapLeft) * ((newfraction - 0.25f)/0.25f),
bitmapTop, paint);
//  path.lineTo(bitmapLeft + (bitmapRight - bitmapLeft) * ((newfraction - 0.25f)/0.25f),
//         bitmapTop);
} else {
canvas.drawLine(bitmapLeft, bitmapTop, bitmapRight, bitmapTop, paint);
// path.lineTo(bitmapRight, bitmapTop);
}
}
if (newfraction > 0.50) {
if (newfraction <= 0.75) {
canvas.drawLine(bitmap
d124
Right, bitmapTop, bitmapRight,
bitmapTop + (bitmapBottom - bitmapTop) * ((newfraction - 0.50f) / 0.25f),
paint);
//path.lineTo(bitmapRight, bitmapTop + (bitmapBottom - bitmapTop) * ((fraction - 0.50f) / 0.25f));
} else {
canvas.drawLine(bitmapRight, bitmapTop, bitmapRight, bitmapBottom, paint);
//path.lineTo(bitmapRight, bitmapBottom);
}
}
if (newfraction > 0.75) {
if (newfraction <= 1) {
canvas.drawLine(bitmapRight, bitmapBottom, bitmapRight - (bitmapRight - bitmapLeft) * ((newfraction - 0.75f)/ 0.25f),
bitmapBottom, paint);
// path.lineTo(bitmapLeft + (bitmapRight - bitmapLeft) * ((fraction - 0.75f)/ 0.25f),
//         bitmapBottom);
} else {
canvas.drawLine(bitmapRight, bitmapBottom, bitmapLeft, bitmapBottom, paint);
// path.lineTo(bitmapLeft, bitmapBottom);
}
}
}
canvas.restore();
canvas.save();
if (fraction > 0.75) {
canvas.clipRect(bitmapLeft + (bitmap.getWidth()/2f) * ((1 - fraction) /0.25f),
bitmapTop + (bitmap.getHeight()/2f)* ((1 - fraction) / 0.25f),
bitmapRight - (bitmap.getWidth()/2f) * ((1 - fraction) /0.25f),
bitmapBottom - (bitmap.getHeight()/2f)* ((1 - fraction) / 0.25f));
Matrix matrix = new Matrix();
matrix.postScale(1.7f, 1.7f, (bitmapLeft + bitmapRight) * 0.5f,
(bitmapTop + bitmapBottom) * 0.5f);
canvas.concat(matrix);
canvas.drawBitmap(bitmap, (bitmapLeft + bitmapRight) / 2 - bitmap.getWidth() / 2,
(bitmapTop + bitmapBottom) / 2 - bitmap.getHeight() / 2, paint);
}
canvas.restore();
}

@Override
public void drawAppStatement(Canvas canvas, float fraction, String statement, int colorOfStatement,
WidthAndHeightOfView widthAndHeightOfView) {
canvas.save();
int width = widthAndHeightOfView.getWidth();
int height = widthAndHeightOfView.getHeight();
Paint paint = new Paint(Paint.ANTI_ALIAS_FLAG);
paint.setColor(colorOfStatement);
paint.setStyle(Paint.Style.STROKE);
paint.setTextSize(45);
paint.setTextSkewX(-0.2f);
paint.setTextAlign(Paint.Align.CENTER);
RectF rectF = new RectF(width / 4 - statement.length(), height * 7 / 8,
width * 3, height);
if (fraction <= 0.60f) {
Path path = new Path();
path.addArc(rectF,193,40 * fraction * 1.67f);
canvas.drawPath(path, paint);
} else {
Path path = new Path();
path.addArc(rectF, 193, 40);
canvas.drawPath(path, paint);
canvas.drawTextOnPath(statement, path, 0, 0, paint);
}
canvas.restore();
}
}

示例

这是选择策略的方法

/**
* 开放绘制策略接口，可由用户自行定义
* @param drawStrategy 绘制接口
* @return Builder对象
*/
public Builder setDrawStategy(DrawStrategy drawStrategy) {
mOpeningStartAnimation.mDrawStrategy = drawStrategy;
return this;
}

策略的具体实现

@Override
protected void onDraw(Canvas canvas) {
canvas.drawColor(colorOfBackground); //绘制背景色
super.onDraw(canvas);
mWidthAndHeightOfView.setHeight(getHeight());
mWidthAndHeightOfView.setWidth(getWidth());
mDrawStrategy.drawAppIcon(canvas, fraction, mDrawable, colorOfAppIcon,
mWidthAndHeightOfView);
mDrawStrategy.drawAppName(canvas, fraction, appName, colorOfAppName,
mWidthAndHeightOfView);
mDrawStrategy.drawAppStatement(canvas, fraction, appStatement, colorOfAppStatement,
mWidthAndHeightOfView);
}

具体项目可见

项目地址