扣丁学堂——绘制几何图型图片

一丶代码见本文（这几节只做了解）

public class MyView extends View {

    public MyView(Context context) {
        super(context);
    }

    //会在组件加载时调用
    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        /* 设置背景为白色 */
        canvas.drawColor(Color.WHITE);
        Paint paint = new Paint();//创建画笔
        /* 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 */
        //参数:圆心x,圆心y,半径r,paint
        canvas.drawCircle(40, 40, 30, paint);
        /* 画一个空心正方形 */
        //参数:left top right bottom ,当right-left等于bottom-top就为正方形 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 */
        /*
        LinearGradient shader = new LinearGradient(0, 0, endX, endY, new int[]{startColor, midleColor, endColor},new float[]{0 , 0.5f, 1.0f}, TileMode.MIRROR);
        参数一为渐变起初点坐标x位置,参数二为y轴位置,参数三和四分别对应渐变终点
        其中参数new int[]{startColor, midleColor, endColor}是参与渐变效果的颜色集合,
        其中参数new float[]{0 , 0.5f, 1.0f}是定义每个颜色处于的渐变相对位置, 这个参数可以为null,如果为null表示所有的颜色按顺序均匀的分布
        最后参数为平铺方式,这里设置为MIRROR镜像(REPEAT重复)
        */
        Shader mShader = new LinearGradient(0, 0, 100, 100, new int[]{
                Color.RED, Color.GREEN, Color.BLUE, Color.YELLOW}, null,
                Shader.TileMode.MIRROR);
        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("圆形", 240, 50,
                paint);
        canvas.drawText("正方形", 240, 120,
                paint);
        canvas.drawText("长方形", 240, 190,
                paint);
        canvas.drawText("椭圆形", 240, 250,
                paint);
        canvas.drawText("三角形", 240, 320,
                paint);
        canvas.drawText("梯形", 240, 390,
                paint);
    }
}

MainActivity

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(new MyView(this));
//        setContentView(new MyImageView(this));
//        setContentView(new MySurfaceView(this));
    }
}