在UI这一块，谈到自定义，就离不开画笔和画布的使用话题，在自定义控件的时候，为了做出炫酷的效果，我们往往会使用画笔和画布，那么这里我们就先来看看画笔的使用吧

简单使用例子

自定义一个View

public class PaintView extends View {private Paint mPaint;public PaintView(Context context, @Nullable AttributeSet attrs) {super(context, attrs);mPaint = new Paint();}@Overrideprotected void onDraw(Canvas canvas) {super.onDraw(canvas);//重置mPaint.reset();//画笔设置mPaint.setColor(Color.RED);mPaint.setAlpha(255);//样式设置
//        mPaint.setStyle(Paint.Style.FILL);//填充mPaint.setStyle(Paint.Style.STROKE);//描边
//        mPaint.setStyle(Paint.Style.FILL_AND_STROKE);//填充及描边//画笔宽度设置mPaint.setStrokeWidth(20);//线帽设置mPaint.setStrokeCap(Paint.Cap.BUTT);//无
//        mPaint.setStrokeCap(Paint.Cap.ROUND);//圆形
//        mPaint.setStrokeCap(Paint.Cap.SQUARE);//方形//线条交叉处
//        mPaint.setStrokeJoin(Paint.Join.BEVEL);//直角
//        mPaint.setStrokeJoin(Paint.Join.ROUND);//圆角
//        mPaint.setStrokeJoin(Paint.Join.MITER);//锐角Path path = new Path();path.moveTo(100,100);path.lineTo(300,100);path.lineTo(500,300);mPaint.setStrokeJoin(Paint.Join.BEVEL);canvas.drawPath(path,mPaint);path.moveTo(100,400);path.lineTo(300,400);path.lineTo(500,700);mPaint.setStrokeJoin(Paint.Join.MITER);canvas.drawPath(path,mPaint);path.moveTo(100,800);path.lineTo(300,800);path.lineTo(500,1100);mPaint.setStrokeJoin(Paint.Join.ROUND);canvas.drawPath(path,mPaint);}
}

画了三条线

Paint的使用说明

Paint在是使用的时候，一般会有两个类参与，一个负责图形绘制，一个负责文字绘制
在使用前一般重置Paint，调用reset()
设置方法一般都对应着获取方法

图形绘制相关方法

• 设置颜色

mPaint.setColor(Color.RED);

• 设置透明度0~255

mPaint.setAlpha(255);

• 设置画笔的样式

mPaint.setStyle(Paint.Style.FILL);//填充
//mPaint.setStyle(Paint.Style.STROKE);//描边
//mPaint.setStyle(Paint.Style.FILL_AND_STROKE);//填充及描边

• 设置画笔的宽度

mPaint.setStrokeWidth(50);

• 设置线帽

mPaint.setStrokeCap(Paint.Cap.BUTT);//无
//mPaint.setStrokeCap(Paint.Cap.ROUND);//圆形
//mPaint.setStrokeCap(Paint.Cap.SQUARE);//方形

• 设置线条交叉处样式

mPaint.setStrokeJoin(Paint.Join.BEVEL);//直角
//mPaint.setStrokeJoin(Paint.Join.ROUND);//圆角
//mPaint.setStrokeJoin(Paint.Join.MITER);//锐角

• 设置防锯齿

mPaint.setAntiAlias(true);

• 设置图像抖动处理

mPaint.setDither(true);

文字绘制相关方法

• 设置字符行间距

mPaint.setFontSpacing(5);

• 设置字符之间的间距

mPaint.getLetterSpacing(5);

• 设置文本删除线

mPaint.setStrikeThruText(true);

• 设置下划线

mPaint.setUnderlineText(true);

• 设置文本大小

mPaint.setTextSize(textSize);

• 设置字体类型

mPaint.setTypeface(Typeface.BOLD);

• 加载自定义字体

Typeface.create(familyName, style);

• 设置文字倾斜,默认0，官方推荐的-0.25f是斜体

mPaint.setTextSkewX(-0.25f);

• 设置文本对齐方式

mPaint.setTextAlign(Align.LEFT);
mPaint.setTextAlign(Align.CENTER);
mPaint.setTextAlign(Align.RIGHT);

• 计算制定长度的字符串（字符长度、字符个数、显示的时候真实的长度）

int breadText = mPaint.breakText(text, measureForwards, maxWidth, measuredWidth);

• 获取文本的矩形区域（宽高）Rect bounds

mPaint.getTextBounds(text, index, count, bounds)
mPaint.getTextBounds(text, start, end, bounds)

• 获取文本的宽度，比较粗略

float measureText = mPaint.measureText(str);

• 获取文本的宽度，比较精准

int textWidths = mPaint.getTextWidths(str, measuredWidth);

文本的基线问题

在绘制文本的时候，事宜基准线为准的，但有时我们在绘制的时候又不以基准线稳准，那么就需要通过计算去获得位置了

canvas.drawText(x,y)这个y并不是text的左上角，而是以baseline为基准的
通过获得相对于基准线的位置，从而计算出需要的位置，负值表示在基准线上方，正值表示在基准线下方

FontMetrics fontMetrics = mPaint.getFontMetrics();
fontMetrics.top;
fontMetrics.ascent;
fontMetrics.descent;
fontMetrics.bottom;

自定义ProgressBar实现

定义自定义属性

<?xml version="1.0" encoding="utf-8"?>
<resources><declare-styleable name="CustomProgressBar"><attr name="roundProgressColor" format="color" /><attr name="roundColor" format="color" /><attr name="roundWidth" format="dimension" /><attr name="textSize" format="dimension" /><attr name="textColor" format="color" /><attr name="max" format="integer" /><attr name="min" format="integer" /><attr name="textShow" format="boolean" /><attr name="style"><enum name="STROKE" value="0" /><enum name="FILL" value="1" /></attr></declare-styleable>
</resources>

自定义ProgressBar

public class CustomProgressBar extends View {public static final int STROKE = 0;public static final int FILL = 1;private int min;private int roundColor;private int roundProgressColor;private float roundWidth;private int style;private int textColor;private boolean textShow;private float textSize;private Paint paint;private int max;private int progress;public CustomProgressBar(Context context, @Nullable AttributeSet attrs) {super(context, attrs);//定义画笔paint = new Paint();//获得自定义属性TypedArray typedArray = context.obtainStyledAttributes(attrs, R.styleable.CustomProgressBar);max = typedArray.getInteger(R.styleable.CustomProgressBar_max, 100);min = typedArray.getInteger(R.styleable.CustomProgressBar_min, 80);roundColor = typedArray.getColor(R.styleable.CustomProgressBar_roundColor, Color.RED);roundProgressColor = typedArray.getColor(R.styleable.CustomProgressBar_roundProgressColor, Color.GRAY);roundWidth = typedArray.getDimension(R.styleable.CustomProgressBar_roundWidth, 10);style = typedArray.getInt(R.styleable.CustomProgressBar_style, 0);textColor = typedArray.getColor(R.styleable.CustomProgressBar_textColor, Color.GREEN);textShow = typedArray.getBoolean(R.styleable.CustomProgressBar_textShow, true);textSize = typedArray.getDimension(R.styleable.CustomProgressBar_textSize, 15);typedArray.recycle();}@Overrideprotected void onDraw(Canvas canvas) {super.onDraw(canvas);//画默认的外层圆环int center = getWidth() / 2;float radius = center - roundWidth / 2;paint.setColor(roundColor);paint.setStyle(Paint.Style.STROKE);paint.setStrokeWidth(roundWidth);paint.setAntiAlias(true);canvas.drawCircle(center, center, radius, paint);//画进度百分比paint.setColor(textColor);paint.setStrokeWidth(0);paint.setTextSize(textSize);paint.setTypeface(Typeface.DEFAULT_BOLD);int precent = (int) (progress / (float) max * 100);if (textShow && style == STROKE) {canvas.drawText(precent + "%", (getWidth() - paint.measureText(precent + "%s")) / 2F,(getHeight() - (paint.descent() + paint.ascent())) / 2F, paint);}//画圆弧paint.setColor(roundProgressColor);paint.setStrokeWidth(roundWidth);RectF oval = new RectF(center - radius, center - radius, center + radius, center + radius);switch (style) {case STROKE:paint.setStyle(Paint.Style.STROKE);canvas.drawArc(oval, 0, 360 * precent / 100, false, paint);break;case FILL:paint.setStyle(Paint.Style.FILL_AND_STROKE);canvas.drawArc(oval, 0, 360 * precent / 100, true, paint);break;}}public int getMin() {return min;}public void setMin(int min) {this.min = min;}public synchronized int getMax() {return max;}public synchronized void setMax(int max) {if (max < 0) {throw new IllegalArgumentException("max不能小于0");}this.max = max;}public synchronized int getProgress() {return progress;}public synchronized void setProgress(int progress) {if (progress < 0) {throw new IllegalArgumentException("progress不能小于0");}if (progress > max) {progress = max;}if (progress <= max) {this.progress = progress;//更新postInvalidate();}}public int getRoundColor() {return roundColor;}public void setRoundColor(int roundColor) {this.roundColor = roundColor;}public int getRoundProgressColor() {return roundProgressColor;}public void setRoundProgressColor(int roundProgressColor) {this.roundProgressColor = roundProgressColor;}public float getRoundWidth() {return roundWidth;}public void setRoundWidth(float roundWidth) {this.roundWidth = roundWidth;}public int getStyle() {return style;}public void setStyle(int style) {this.style = style;}public int getTextColor() {return textColor;}public void setTextColor(int textColor) {this.textColor = textColor;}public boolean isTextShow() {return textShow;}public void setTextShow(boolean textShow) {this.textShow = textShow;}public float getTextSize() {return textSize;}public void setTextSize(float textSize) {this.textSize = textSize;}
}

编写布局

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"xmlns:myApp="http://schemas.android.com/apk/res-auto"android:layout_width="match_parent"android:layout_height="match_parent"><com.cj5785.painttest.CustomProgressBarandroid:id="@+id/custom_progress_bar"android:layout_centerInParent="true"android:layout_width="100dp"android:layout_height="100dp"myApp:roundProgressColor="@android:color/holo_green_light"myApp:roundColor="@android:color/holo_blue_light"myApp:roundWidth="10dp"myApp:textColor="@android:color/holo_orange_light"myApp:textSize="18sp" /><Buttonandroid:layout_alignParentBottom="true"android:layout_width="match_parent"android:layout_height="wrap_content"android:onClick="start"/></RelativeLayout>

测试

public class ProgressBarActivity extends AppCompatActivity {private CustomProgressBar progressBar;private int progess;@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_progress_bar);progressBar = findViewById(R.id.custom_progress_bar);}public void start(View view) {progess += 5;progressBar.setProgress(progess);}
}

效果如下

附录 API

public class Paint extends Object
java.lang.Object
​ ↳android.graphics.Paint

The Paint class holds the style and color information about how to draw geometries, text and bitmaps.

Nested classes
enum	Paint.Align Align specifies how drawText aligns its text relative to the [x,y] coordinates.
enum	Paint.Cap The Cap specifies the treatment for the beginning and ending of stroked lines and paths.
class	Paint.FontMetrics Class that describes the various metrics for a font at a given text size.
class	Paint.FontMetricsInt Convenience method for callers that want to have FontMetrics values as integers.
enum	Paint.Join The Join specifies the treatment where lines and curve segments join on a stroked path.
enum	Paint.Style The Style specifies if the primitive being drawn is filled, stroked, or both (in the same color).

Constants
int	ANTI_ALIAS_FLAG Paint flag that enables antialiasing when drawing.
int	DEV_KERN_TEXT_FLAG Legacy Paint flag, no longer used.
int	DITHER_FLAG Paint flag that enables dithering when blitting.
int	EMBEDDED_BITMAP_TEXT_FLAG Paint flag that enables the use of bitmap fonts when drawing text.
int	FAKE_BOLD_TEXT_FLAGPaint flag that applies a synthetic bolding effect to drawn text.
int	FILTER_BITMAP_FLAG Paint flag that enables bilinear sampling on scaled bitmaps.
int	HINTING_OFF Font hinter option that disables font hinting.
int	HINTING_ON Font hinter option that enables font hinting.
int	LINEAR_TEXT_FLAG Paint flag that enables smooth linear scaling of text.
int	STRIKE_THRU_TEXT_FLAG Paint flag that applies a strike-through decoration to drawn text.
int	SUBPIXEL_TEXT_FLAG Paint flag that enables subpixel positioning of text.
int	UNDERLINE_TEXT_FLAG Paint flag that applies an underline decoration to drawn text.

Public constructors

Paint() Create a new paint with default settings.

Paint(int flags) Create a new paint with the specified flags.

Paint(Paint paint) Create a new paint, initialized with the attributes in the specified paint parameter.

Public methods
float	ascent() Return the distance above (negative) the baseline (ascent) based on the current typeface and text size.
int	breakText(char[] text, int index, int count, float maxWidth, float[] measuredWidth) Measure the text, stopping early if the measured width exceeds maxWidth.
int	breakText(String text, boolean measureForwards, float maxWidth,float[] measuredWidth) Measure the text, stopping early if the measured width exceeds maxWidth.
int	breakText(CharSequence text, int start, int end, boolean measureForwards, float maxWidth, float[] measuredWidth) Measure the text, stopping early if the measured width exceeds maxWidth.
void	clearShadowLayer() Clear the shadow layer.
float	descent() Return the distance below (positive) the baseline (descent) based on the current typeface and text size.
boolean	equalsForTextMeasurement(Paint other)Returns true of the passed Paint will have the same effect on text measurement
int	getAlpha()Helper to getColor() that just returns the color’s alpha value.
int	getColor()Return the paint’s color.
ColorFilter	getColorFilter()Get the paint’s colorfilter (maybe be null).
boolean	getFillPath(Path src, Path dst)Applies any/all effects (patheffect, stroking) to src, returning the result in dst.
int	getFlags()Return the paint’s flags.
String	getFontFeatureSettings()Returns the font feature settings.
float	getFontMetrics(Paint.FontMetrics metrics)Return the font’s recommended interline spacing, given the Paint’s settings for typeface, textSize, etc.
Paint.FontMetrics	getFontMetrics()Allocates a new FontMetrics object, and then calls getFontMetrics(fm) with it, returning the object.
int	getFontMetricsInt(Paint.FontMetricsInt fmi)Return the font’s interline spacing, given the Paint’s settings for typeface, textSize, etc.
Paint.FontMetricsInt	getFontMetricsInt()
float	getFontSpacing()Return the recommend line spacing based on the current typeface and text size.
String	getFontVariationSettings()Returns the font variation settings.
int	getHinting()Return the paint’s hinting mode.
float	getLetterSpacing()Return the paint’s letter-spacing for text.
MaskFilter	getMaskFilter()Get the paint’s maskfilter object.
int	getOffsetForAdvance(char[] text, int start, int end, int contextStart,int contextEnd, boolean isRtl, float advance)Get the character offset within the string whose position is closest to the specified horizontal position.
int	getOffsetForAdvance(CharSequence text, int start, int end, int contextStart, int contextEnd, boolean isRtl, float advance)
PathEffect	getPathEffect()Get the paint’s patheffect object.
float	getRunAdvance(char[] text, int start, int end, int contextStart, int contextEnd, boolean isRtl, int offset)Measure cursor position within a run of text.
float	getRunAdvance(CharSequence text, int start, int end, int contextStart,int contextEnd, boolean isRtl, int offset)
Shader	getShader()Get the paint’s shader object.
Paint.Cap	getStrokeCap()Return the paint’s Cap, controlling how the start and end of stroked lines and paths are treated.
Paint.Join	getStrokeJoin()Return the paint’s stroke join type.
float	getStrokeMiter()Return the paint’s stroke miter value.
float	getStrokeWidth()Return the width for stroking.
Paint.Style	getStyle()Return the paint’s style, used for controlling how primitives’ geometries are interpreted (except for drawBitmap, which always assumes FILL_STYLE).
Paint.Align	getTextAlign()Return the paint’s Align value for drawing text.
void	getTextBounds(String text, int start, int end, Rect bounds)Return in bounds (allocated by the caller) the smallest rectangle that encloses all of the characters, with an implied origin at (0,0).
void	getTextBounds(char[] text, int index, int count, Rect bounds)Return in bounds (allocated by the caller) the smallest rectangle that encloses all of the characters, with an implied origin at (0,0).
Locale	getTextLocale()Get the text’s primary Locale.
LocaleList	getTextLocales()Get the text locale list.
void	getTextPath(char[] text, int index, int count, float x, float y, Pathpath)Return the path (outline) for the specified text.
void	getTextPath(String text, int start, int end, float x, float y, Pathpath)Return the path (outline) for the specified text.
float	getTextScaleX()Return the paint’s horizontal scale factor for text.
float	getTextSize()Return the paint’s text size.
float	getTextSkewX()Return the paint’s horizontal skew factor for text.
int	getTextWidths(char[] text, int index, int count, float[] widths)Return the advance widths for the characters in the string.
int	getTextWidths(String text, float[] widths)Return the advance widths for the characters in the string.
int	getTextWidths(String text, int start, int end, float[] widths)Return the advance widths for the characters in the string.
int	getTextWidths(CharSequence text, int start, int end, float[] widths)Return the advance widths for the characters in the string.
Typeface	getTypeface()Get the paint’s typeface object.
Xfermode	getXfermode()Get the paint’s transfer mode object.
boolean	hasGlyph(String string)Determine whether the typeface set on the paint has a glyph supporting the string.
final boolean	isAntiAlias()Helper for getFlags(), returning true if ANTI_ALIAS_FLAG bit is set AntiAliasing smooths out the edges of what is being drawn, but is has no impact on the interior of the shape.
final boolean	isDither()Helper for getFlags(), returning true if DITHER_FLAG bit is set Dithering affects how colors that are higher precision than the device are down-sampled.
boolean	isElegantTextHeight()Get the elegant metrics flag.
final boolean	isFakeBoldText()Helper for getFlags(), returning true if FAKE_BOLD_TEXT_FLAG bit is set
final boolean	isFilterBitmap()Whether or not the bitmap filter is activated.
final boolean	isLinearText()Helper for getFlags(), returning true if LINEAR_TEXT_FLAG bit is set
final boolean	isStrikeThruText()Helper for getFlags(), returning true if STRIKE_THRU_TEXT_FLAG bit is set
final boolean	isSubpixelText()Helper for getFlags(), returning true if SUBPIXEL_TEXT_FLAG bit is set
final boolean	isUnderlineText()Helper for getFlags(), returning true if UNDERLINE_TEXT_FLAG bit is set
float	measureText(char[] text, int index, int count)Return the width of the text.
float	measureText(CharSequence text, int start, int end)Return the width of the text.
float	measureText(String text, int start, int end)Return the width of the text.
float	measureText(String text)Return the width of the text.
void	reset()Restores the paint to its default settings.
void	set(Paint src)Copy the fields from src into this paint.
void	setARGB(int a, int r, int g, int b)Helper to setColor(), that takes a,r,g,b and constructs the color int
void	setAlpha(int a)Helper to setColor(), that only assigns the color’s alpha value, leaving its r,g,b values unchanged.
void	setAntiAlias(boolean aa)Helper for setFlags(), setting or clearing the ANTI_ALIAS_FLAG bit AntiAliasing smooths out the edges of what is being drawn, but is has no impact on the interior of the shape.
void	setColor(int color)Set the paint’s color.
ColorFilter	setColorFilter(ColorFilter filter)Set or clear the paint’s colorfilter, returning the parameter.
void	setDither(boolean dither)Helper for setFlags(), setting or clearing the DITHER_FLAG bit Dithering affects how colors that are higher precision than the device are down-sampled.
void	setElegantTextHeight(boolean elegant)Set the paint’s elegant height metrics flag.
void	setFakeBoldText(boolean fakeBoldText)Helper for setFlags(), setting or clearing the FAKE_BOLD_TEXT_FLAG bit
void	setFilterBitmap(boolean filter)Helper for setFlags(), setting or clearing the FILTER_BITMAP_FLAG bit.
void	setFlags(int flags)Set the paint’s flags.
void	setFontFeatureSettings(String settings)Set font feature settings.
boolean	setFontVariationSettings(String fontVariationSettings)Sets TrueType or OpenType font variation settings.
void	setHinting(int mode)Set the paint’s hinting mode.
void	setLetterSpacing(float letterSpacing)Set the paint’s letter-spacing for text.
void	setLinearText(boolean linearText)Helper for setFlags(), setting or clearing the LINEAR_TEXT_FLAG bit
MaskFilter	setMaskFilter(MaskFilter maskfilter)Set or clear the maskfilter object.
PathEffect	setPathEffect(PathEffect effect)Set or clear the patheffect object.
Shader	setShader(Shader shader)Set or clear the shader object.
void	setShadowLayer(float radius, float dx, float dy, int shadowColor)This draws a shadow layer below the main layer, with the specified offset and color, and blur radius.
void	setStrikeThruText(boolean strikeThruText)Helper for setFlags(), setting or clearing the STRIKE_THRU_TEXT_FLAG bit
void	setStrokeCap(Paint.Cap cap)Set the paint’s Cap.
void	setStrokeJoin(Paint.Join join)Set the paint’s Join.
void	setStrokeMiter(float miter)Set the paint’s stroke miter value.
void	setStrokeWidth(float width)Set the width for stroking.
void	setStyle(Paint.Style style)Set the paint’s style, used for controlling how primitives’ geometries are interpreted (except for drawBitmap, which always assumes Fill).
void	setSubpixelText(boolean subpixelText)Helper for setFlags(), setting or clearing the SUBPIXEL_TEXT_FLAG bit
void	setTextAlign(Paint.Align align)Set the paint’s text alignment.
void	setTextLocale(Locale locale)Set the text locale list to a one-member list consisting of just the locale.
void	setTextLocales(LocaleList locales)Set the text locale list.
void	setTextScaleX(float scaleX)Set the paint’s horizontal scale factor for text.
void	setTextSize(float textSize)Set the paint’s text size.
void	setTextSkewX(float skewX)Set the paint’s horizontal skew factor for text.
Typeface	setTypeface(Typeface typeface)Set or clear the typeface object.
void	setUnderlineText(boolean underlineText)Helper for setFlags(), setting or clearing the UNDERLINE_TEXT_FLAG bit
Xfermode	setXfermode(Xfermode xfermode)Set or clear the transfer mode object.