绘制几何图形——使用android.graphics类 onDraw

范例说明

“如何在和机上绘制2D图形呢？”这是许多android游戏开发都是常提到的问题，在android SDK 当中，并没有Java Graphics2D的函数可以使用，而是使用android.graphics底下的类来绘制2D向量图。这个package提供了许多在手机上绘制图 形的类与方法，其中Canvas上，而Paint（Android.graphics.Paint)类则像是彩色铅笔，给予不同的调协，即可绘制不同颜 色、不同种类效果的向量图形。

本范例将运用Paint对象（绘笔）的设置值不同，在Cavas(画布）上绘制空心、实习及渐变色的多种几何多形。

运行结果如果

范例程序

主程序中继承自Android.view.View的 MyView类，重写 MyView的onDraw（）方法，一开始就会运行绘制的工作，在onDraw（）中以Paint将几何图形绘制在Canvas上，以 paint.setColor() 改变图形颜色、以 paint.setStyle()的设置来控制画出的的图形是空心还是实心。程序的最后一段，就是直接在Canvas写上文字，随着Paint对象里的属 性设置，也会有不同的外观模式。

package com.graphics;
import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.RectF;
import android.graphics.Path;
import android.graphics.Shader;
import android.graphics.LinearGradient;
public class GraphicesActivity extends Activity {
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        /*设置ContentView为自定义的MyVieW*/
        MyView myView=new MyView(this);
        setContentView(myView);
    }
    /* 自定义继承View 的MyView*/
private class MyView extends View
{
     public MyView(Context context){
        super(context) ;
     }
     /*重写onDraw（）*/
     @Override
     protected void onDraw(Canvas canvas)
     {   
         super.onDraw(canvas);
         /*设置背景为白色*/
         canvas.drawColor(Color.WHITE);
          Paint paint=new Paint();
          /*去锯齿*/
          paint.setAntiAlias(true);
          /*设置paint的颜色*/
          paint.setColor(Color.RED);
          /*设置paint的 style 为STROKE：空心*/
          paint.setStyle(Paint.Style.STROKE);
          /*设置paint的外框宽度*/
          paint.setStrokeWidth(3);
          /*画一个空心圆形*/
          canvas.drawCircle(40, 40, 30, paint);
          /*画一个空心正方形*/
          canvas.drawRect(10, 90, 70, 150, paint);
          /*画一个空心长方形*/
          canvas.drawRect(10, 170, 70,200, paint);
          /*画一个空心椭圆形*/
          RectF re=new RectF(10,220,70,250);
          canvas.drawOval(re, paint);
          /*画一个空心三角形*/
          Path path=new Path();
          path.moveTo(10, 330);
          path.lineTo(70,330);
          path.lineTo(40,270);
          path.close();
          canvas.drawPath(path, paint);
          /*画一个空心梯形*/
          Path path1=new Path();
          path1.moveTo(10, 410);
          path1.lineTo(70,410);
          path1.lineTo(55,350);
          path1.lineTo(25, 350);
          path1.close();
          canvas.drawPath(path1, paint);
          
          /*设置paint 的style为 FILL：实心*/
          paint.setStyle(Paint.Style.FILL);
          /*设置paint的颜色*/
          paint.setColor(Color.BLUE);
          /*画一个实心圆*/
          canvas.drawCircle(120,40,30, paint);
          /*画一个实心正方形*/
          canvas.drawRect(90, 90, 150, 150, paint);
          /*画一个实心长方形*/
          canvas.drawRect(90, 170, 150,200, paint);
          /*画一个实心椭圆*/
          RectF re2=new RectF(90,220,150,250);
          canvas.drawOval(re2, paint);
          /*画一个实心三角形*/
          Path path2=new Path();
          path2.moveTo(90, 330);
          path2.lineTo(150,330);
          path2.lineTo(120,270);
          path2.close();
          canvas.drawPath(path2, paint);
          /*画一个实心梯形*/
          Path path3=new Path();
          path3.moveTo(90, 410);
          path3.lineTo(150,410);
          path3.lineTo(135,350);
          path3.lineTo(105, 350);
          path3.close();
          canvas.drawPath(path3, paint);
          /*设置渐变色*/
          Shader mShader=new LinearGradient(0,0,100,100,
                  new int[]{Color.RED,Color.GREEN,Color.BLUE,Color.YELLOW},
                  null,Shader.TileMode.REPEAT);
          paint.setShader(mShader);
        
          /*画一个渐变色圆*/
          canvas.drawCircle(200,40,30, paint);
          /*画一个渐变色正方形*/
          canvas.drawRect(170, 90, 230, 150, paint);
          /*画一个渐变色长方形*/
          canvas.drawRect(170, 170, 230,200, paint);
          /*画一个渐变色椭圆*/
          RectF re3=new RectF(170,220,230,250);
          canvas.drawOval(re3, paint);
          /*画一个渐变色三角形*/
          Path path4=new Path();
          path4.moveTo(170,330);
          path4.lineTo(230,330);
          path4.lineTo(200,270);
          path4.close();
          canvas.drawPath(path4, paint);
          /*画一个渐变色梯形*/
          Path path5=new Path();
          path5.moveTo(170, 410);
          path5.lineTo(230,410);
          path5.lineTo(215,350);
          path5.lineTo(185, 350);
          path5.close();
          canvas.drawPath(path5, paint);
          
          /*写字*/
          paint.setTextSize(24);
          canvas.drawText(getResources().getString(R.string.str_text1), 240, 50, paint);
          canvas.drawText(getResources().getString(R.string.str_text2), 240, 120, paint);
          canvas.drawText(getResources().getString(R.string.str_text3), 240, 190, paint);
          canvas.drawText(getResources().getString(R.string.str_text4), 240, 250, paint);
          canvas.drawText(getResources().getString(R.string.str_text5), 240, 320, paint);
          canvas.drawText(getResources().getString(R.string.str_text6), 240, 390, paint);  
     }
}
}

转自：http://www.cnblogs.com/stulife/archive/2010/08/19/1803313.html