前言
在Android开发中经常会遇到特殊的需求要求开发者实现独特的视图UI。所以对于开发者来说自定义View可以实现多种多样的需求效果。那这次我们就来说说关于自定义View的实现。
View绘制原理
View的绘制是在方法onDraw中实现的。通过获取View的画布canvas，使用Panit在canvas上绘制内容。
public class CustomerView extends View {
@Override
protected void onDraw(Canvas canvas) {
}
}
画笔Panit
就和我们实际画画一样，绘制需要一支画笔才行。Paint就是我们绘制所需要的画笔。实例化Paint并设置绘制所需要的参数就能绘制出自己所需要的内容。Android开发文档中Paint实现方法很多，这里我们介绍几个常用基本的方法。
setAlpha(bookean a) //设置抗锯齿
setColor(int color) //设置画笔颜色
setShader(Shader shader)//设置画笔渐变颜色
setStyle(Paint.Style style)//设置画笔模式（例如实心/空心）
setXfermode(Xfermode xfermode)//设置画笔绘制模式
setStrokeWidth(float width) //设置画笔粗细
画布Canvas
有了画笔，现在就是要用画笔在画布上画画了。想要绘制怎么样的图形是通过Canvas的方法实现的。我们也介绍几个常用基本的绘制方法。只要理科学的好人人都是现代派画家O(∩_∩)O~。
drawARGB(int a, int r, int g, int b)//设置画布背景颜色
drawColor(int color)//设置画布背景颜色
drawRect(float left, float top, float right, float bottom, Paint paint)//绘制矩形
drawPath(Path path, Paint paint)//绘制自定义图形
drawCircle(float cx, float cy, float radius, Paint paint)//绘制原型
drawArc(float left, float top, float right, float bottom, float startAngle, float sweepAngle, boolean useCenter, Paint paint)//绘制弧以及圆
drawLine(float startX, float startY, float stopX, float stopY, Paint paint)//绘制线条
drawText(String text, int start, int end, float x, float y, Paint paint)//绘制文字
drawPoint(float x, float y, Paint paint)//绘制点
drawRoundRect(float left, float top, float right, float bottom, float rx, float ry, Paint paint)//绘制圆角矩形
drawOval(RectF oval, Paint paint)//绘制圆
drawBitmap(Bitmap bitmap, float left, float top, Paint paint) //绘制图片
画起来
知道了画笔Paint和画布Canavs的基本方法，最后我们实践画一画为成为画家迈出第一步。
public class NormalView extends BaseView {
Path triangle2;
Path all;
private float[] mTickRightStartPosition = new float[2];
public NormalView(Context context) {
super(context);
}
public NormalView(Context context, AttributeSet attrs) {
super(context, attrs);
}
public NormalView(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
}
void initView(){
mPaint = new Paint();
mPaint.setColor(Color.BLACK);
mPaint.setStrokeWidth(5);
mPaint.setAntiAlias(true);
}
@Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
mCanVas = canvas;
//绘制正方形
mCanVas.drawRect(20,40,60,80,mPaint);
//绘制矩形
mCanVas.drawRect(20,100,60,160,mPaint);
//绘制三角形
Path path = new Path();
path.moveTo(60, 200);// 此点为多边形的起点
path.lineTo(40, 250);
path.lineTo(80, 250);
path.close(); // 使这些点构成封闭的多边形
mCanVas.drawPath(path,mPaint);
//画圆
mCanVas.drawCircle(40,400,40,mPaint);
//画文字
mPaint.setTextSize(50);
mCanVas.drawText("Hello world!",0,12,40,500,mPaint);
//画图片
Bitmap bitmap = BitmapFactory.decodeResource(this.getResources(), R.mipmap.ic_launcher);
mCanVas.drawBitmap(bitmap,40,600,mPaint);
//画背景色
mCanVas.drawARGB(100,100,100,100);
//画弧以及画椭圆
RectF rectF = new RectF();
Rect rect = new Rect(40,750,150,800);
rectF.set(rect);
mCanVas.drawArc(rectF,0,-180,true,mPaint);
//画线
mCanVas.drawLine(40,850,100,900,mPaint);
//画点
mCanVas.drawPoint(40,950,mPaint);
//画圆角矩形
RectF roundRectF = new RectF();
Rect roundRect = new Rect(40,1000,400,1050);
roundRectF.set(roundRect);
mCanVas.drawRoundRect(roundRectF,20,5,mPaint);
//画圆
RectF OvalRectF = new RectF();
Rect OvalRect = new Rect(40,1100,60,1200);
OvalRectF.set(OvalRect);
mCanVas.drawOval(OvalRectF,mPaint);
Path hexagon = new Path();
hexagon.moveTo(40,1400);
hexagon.lineTo(90,1350);
hexagon.lineTo(140,1350);
hexagon.lineTo(190,1400);
hexagon.lineTo(140,1450);
hexagon.lineTo(90,1450);
hexagon.lineTo(40,1400);
hexagon.close();
mCanVas.drawPath(hexagon,mPaint);
Path triangle1 = new Path();
triangle1.moveTo(500,100);
triangle1.lineTo(500,300);
triangle1.lineTo(700,300);
triangle1.lineTo(500,100);
triangle1.close();
triangle2 = new Path();
triangle2.moveTo(700,100);
triangle2.lineTo(900,100);
triangle2.lineTo(900,300);
triangle2.lineTo(700,100);
triangle2.close();
all = new Path();
all.addPath(triangle1);
all.addPath(triangle2);
mCanVas.drawPath(all,mPaint);
}
}
