繪制圓環(huán)其實(shí)很簡(jiǎn)單,有大概以下三種思路. 這里先說(shuō)網(wǎng)上提到的一種方法。思路是先繪制內(nèi)圓,然后繪制圓環(huán)(圓環(huán)的寬度就是paint設(shè)置的paint.setStrokeWidth的寬度),最后繪制外圓。
請(qǐng)看核心源碼:
<SPAN xmlns="http://www.w3.org/1999/xhtml">package yan.guoqi.rectphoto;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Paint.Style;
import android.graphics.RectF;
import android.util.AttributeSet;
import android.widget.ImageView;
public class DrawImageView extends ImageView {
private final Paint paint;
private final Context context;
public DrawImageView(Context context, AttributeSet attrs) {
super(context, attrs);
// TODO Auto-generated constructor stub
this.context = context;
this.paint = new Paint();
this.paint.setAntiAlias(true); //消除鋸齒
this.paint.setStyle(Style.STROKE); //繪制空心圓或 空心矩形
}
@Override
protected void onDraw(Canvas canvas) {
// TODO Auto-generated method stub
int center = getWidth()/2;
int innerCircle = dip2px(context, 83); //內(nèi)圓半徑
int ringWidth = dip2px(context, 10); //圓環(huán)寬度
// 第一種方法繪制圓環(huán)
//繪制內(nèi)圓
this.paint.setARGB(255, 138, 43, 226);
this.paint.setStrokeWidth(2);
canvas.drawCircle(center, center, innerCircle, this.paint);
//繪制圓環(huán)
this.paint.setARGB(255, 138, 43, 226);
this.paint.setStrokeWidth(ringWidth);
canvas.drawCircle(center, center, innerCircle + 1 +ringWidth/2, this.paint);
//繪制外圓
this.paint.setARGB(255, 138, 43, 226);
this.paint.setStrokeWidth(2);
canvas.drawCircle(center, center, innerCircle + ringWidth, this.paint);
super.onDraw(canvas);
}
/* 根據(jù)手機(jī)的分辨率從 dp 的單位 轉(zhuǎn)成為 px(像素) */
public static int dip2px(Context context, float dpValue) {
final float scale = context.getResources().getDisplayMetrics().density;
return (int) (dpValue * scale + 0.5f);
}
}
</SPAN>
總結(jié):
1,這種分三次來(lái)繪制的方法,可以將圓環(huán)的內(nèi)圓 圓環(huán) 和外圓的顏色設(shè)成不一樣的,對(duì)paint進(jìn)行三次設(shè)置。還可以將繪制圓環(huán)的paint透明度設(shè)成10左右就會(huì)有圓環(huán)透明的效果。
2,三次繪制時(shí)的canvas.drawCircle圓心都是(center,center),但三次半徑確實(shí)不一樣的。尤其是第二次繪制圓環(huán)的時(shí)候,半徑是innerCircle + 1 +ringWidth/2。這里的加1是第一次外圓paint.setStrokeWidth(2);寬度設(shè)成2,也就是說(shuō)單條線的寬度1。后面的ringWidth/2也是同理。
示例如下(底色是預(yù)覽攝像頭的視頻):
