Android中自定义常用的三个对象解析（Paint,Color,Canvas）
Paint,Color,Canvas
Paint:画笔对象，画图用的“笔”
Color:颜色，相当于调料
Canvas:画布，现实中的纸板
Paint 画笔
常用的方法就是设置和获取到画笔的样式：
paint.setStyle(); 设置画笔的风格，空心的或者是实心的
paint.setColor(); 设置画笔的颜色
paint.setStrokeWidth(); 设置边框线的宽度
paint.setAlpha(); 设置画笔的Alpha值
paint.setAntiAlias(); 设置画笔的锯齿效果
paint.setTextSize(); 设置字体的大小
paint.getAlpha(); 获取到画笔的Alpha值
paint.getColor(); 获取到画笔的颜色
paint.getTextBounds(); 获取到最小的能包容字体的边框
。。。。。。。Color 颜色
通过Color.颜色名 ,来获取到想要的颜色。
Color里面设置了许多常用的颜色枚举值，比如：
@ColorInt public static final int BLACK = 0xFF000000;
@ColorInt public static final int DKGRAY = 0xFF444444;
@ColorInt public static final int GRAY = 0xFF888888;
@ColorInt public static final int LTGRAY = 0xFFCCCCCC;
@ColorInt public static final int WHITE = 0xFFFFFFFF;
@ColorInt public static final int RED = 0xFFFF0000;
@ColorInt public static final int GREEN = 0xFF00FF00;
@ColorInt public static final int BLUE = 0xFF0000FF;
@ColorInt public static final int YELLOW = 0xFFFFFF00;
@ColorInt public static final int CYAN = 0xFF00FFFF;
@ColorInt public static final int MAGENTA = 0xFFFF00FF;
@ColorInt public static final int TRANSPARENT = 0;同样，也可以自定义想要的颜色：调用Color.argb()
/** * Return a color-int from alpha, red, green, blue components. * These component values should be [0..255], but there is no * range check performed, so if they are out of range, the * returned color is undefined. * @param alpha Alpha component [0..255] of the color * @param red Red component [0..255] of the color * @param green Green component [0..255] of the color * @param blue Blue component [0..255] of the color */
@ColorInt
public static int argb(int alpha, int red, int green, int blue) {
return (alpha << 24) | (red << 16) | (green << 8) | blue;
}Canvas 画布，可以绘制常见的图形，比如圆，直线，矩形
绘制直线：canvas.drawLine();
/**
* Draw a line segment with the specified start and stop x,y coordinates,
* using the specified paint.
*
* <p>Note that since a line is always "framed", the Style is ignored in the paint.</p>
*
* <p>Degenerate lines (length is 0) will not be drawn.</p>
*
* @param startX The x-coordinate of the start point of the line
* @param startY The y-coordinate of the start point of the line
* @param paint The paint used to draw the line
*/
public void **drawLine**(float startX, float startY, float stopX, float stopY,
@NonNull Paint paint)绘制圆：canvas.drawCircle();
/**
* 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
*/
public void **drawCircle**(float cx, float cy, float radius, @NonNull Paint paint)绘制矩形：;canvas.drawRect();
/**
* Draw the specified Rect using the specified paint. The rectangle will
* be filled or framed based on the Style in the paint.
*
* @param left The left side of the rectangle to be drawn
* @param top The top side of the rectangle to be drawn
* @param right The right side of the rectangle to be drawn
* @param bottom The bottom side of the rectangle to be drawn
* @param paint The paint used to draw the rect
*/
public void **drawRect**(float left, float top, float right, float bottom, @NonNull Paint paint)绘制图片：canvas.drawBitmap();
/**
* Draw the specified bitmap, with its top/left corner at (x,y), using
* the specified paint, transformed by the current matrix.
*
* <p>Note: if the paint contains a maskfilter that generates a mask which
* extends beyond the bitmap's original width/height (e.g. BlurMaskFilter),
* then the bitmap will be drawn as if it were in a Shader with CLAMP mode.
* Thus the color outside of the original width/height will be the edge
* color replicated.
*
* <p>If the bitmap and canvas have different densities, this function
* will take care of automatically scaling the bitmap to draw at the
* same density as the canvas.
*
* @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)
*/
public void **drawBitmap**(@NonNull Bitmap bitmap, float left, float top, @Nullable Paint paint) {
throwIfCannotDraw(bitmap)绘制文本：canvas.drawText();
/**
* Draw the text, with origin at (x,y), using the specified paint. The
* origin is interpreted based on the Align setting in the paint.
*
* @param text The text to be drawn
* @param x The x-coordinate of the origin of the text being drawn
* @param y The y-coordinate of the baseline of the text being drawn
* @param paint The paint used for the text (e.g. color, size, style)
*/
public void **drawText**(@NonNull String text, float x, float y, @NonNull Paint paint)绘制圆弧：canvas.drawArc();
/**
* <p>Draw the specified arc, which will be scaled to fit inside the
* specified oval.</p>
*
* <p>If the start angle is negative or >= 360, the start angle is treated
* as start angle modulo 360.</p>
*
* <p>If the sweep angle is >= 360, then the oval is drawn
* completely. Note that this differs slightly from SkPath::arcTo, which
* treats the sweep angle modulo 360. If the sweep angle is negative,
* the sweep angle is treated as sweep angle modulo 360</p>
*
* <p>The arc is drawn clockwise. An angle of 0 degrees correspond to the
* geometric angle of 0 degrees (3 o'clock on a watch.)</p>
*
* @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
*/
public void **drawArc**(@NonNull RectF oval, float startAngle, float sweepAngle, boolean useCenter,
@NonNull Paint paint)。。。。。。。
小结
自定义view的时候一般会重写onDraw()方法，画图时必要的三要素：Color,paint,canvas