Android 自定义View学习(二)(2)_H5之家 - 中国HTML5教程资源分享第一站

RectF holds four float coordinates for a rectangle. The rectangle is represented by the coordinates of its 4 edges (left, top, right bottom). These fields can be accessed directly. Use width() and height() to retrieve
the rectangle's width and height. Note: most methods do not check to see that the coordinates are sorted correctly (i.e. left <= right and top <= bottom).

两者差别就是：Rect 坐标为integer 而RectF 坐标为float

使用：

@Override protected void onDraw(Canvas canvas) { super.onDraw(canvas); Rect rect = new RectF(100,100,200,200); canvas.drawRect(rect,paint); } @Override protected void onDraw(Canvas canvas) { super.onDraw(canvas); RectF rect = new RectF(100.5f,100.5f,200.5f,200.5f); canvas.drawRect(rect,paint); }

注意构造方法中的参数顺序

2.2 drawCricle() 绘制圆形

drawCircle(float cx, float cy, float radius, @NonNull Paint paint)

Draw the specified circle using the specified paint. If radius is <= 0, then nothing will be drawn. The circle will be filled or framed based on the Style in the paint.
@param cx The x-coordinate of the center of the cirle to be drawn
@param cy The y-coordinate of the center of the cirle to be drawn
@param radius The radius of the cirle to be drawn
@param paint The paint used to draw the circle

radius: 半径
cx : 圆心的x坐标
cy : 圆心的y坐标
使用的时候需要考虑圆心和半径

绘制圆形

使用：

@Override protected void onDraw(Canvas canvas) { super.onDraw(canvas); float width = getWidth(); float height = getHeight(); float radius = Math.min(width,height)/2; canvas.drawCircle(width/2,height/2,radius,paint); }

绘制圆形时，半径是宽和高中较小者的二分之一

2.3 drawArc() 绘制扇形

drawArc(float left, float top, float right, float bottom, float startAngle,float sweepAngle, boolean useCenter, @NonNull Paint paint)

drawArc(@NonNull RectF oval, float startAngle, float sweepAngle, boolean useCenter, @NonNull Paint paint)

两个方法的差别：

方法2把坐标封装进RectF对象中

方法1要求系统最低为21

drawArc(@NonNull RectF oval, float startAngle, float sweepAngle, boolean useCenter, @NonNull Paint paint)

@param oval The bounds of oval used to define the shape and size of the arc
@param startAngle Starting angle (in degrees) where the arc begins
@param sweepAngle Sweep angle (in degrees) measured clockwise
@param useCenter If true, include the center of the oval in the arc, and close it if it is being stroked. This will draw a wedge
@param paint The paint used to draw the arc

float startAngle 开始绘制的角度

float sweepAngle 扇形扫过的角度，并不是停止时的角度。停止角度 = startAngle+ sweepAngle

boolean useCenter ture就是有焦点圆心， false 没有

扇形，有焦点圆心

@Override protected void onDraw(Canvas canvas) { super.onDraw(canvas); RectF rect = new RectF(0f,0f,500f,500f); canvas.drawArc(rect,0,60,true,paint); canvas.drawArc(rect,60,30,true,paint_2); }

此时的boolean useCenter为true

当把boolean useCenter设置为false时

扇形无焦点圆形

此时之画出了开始点和结束点两点之间的区域

2.4 drawBitmap() 绘制Bitmap

drawBitmap(@NonNull Bitmap bitmap, float left, float top, @Nullable Paint paint)

@param bitmap The bitmap to be drawn
@param left The position of the left side of the bitmap being drawn
@param top The position of the top side of the bitmap being drawn
@param paint The paint used to draw the bitmap (may be null)

left 左上角横坐标

top 左上角纵坐标

绘制bitmap

@Override protected void onDraw(Canvas canvas) { super.onDraw(canvas); Bitmap bitmap = BitmapFactory.decodeResource(getResources(), R.mipmap.ic_launcher); float width = (getWidth()-bitmap.getWidth())/2; float height = (getHeight()-bitmap.getHeight())/2; canvas.drawBitmap(bitmap,width,height,paint); }

根据left和top确定绘制的位置，此时Paint的用于绘制文字的属性设置在绘制Bitmap时是无效的。

2.5 drawText()绘制文字

drawText(@NonNull String text, float x, float y, @NonNull Paint paint)