mPaint = new Paint();

mPaint.setColor(Color.BLUE);
mPaint.setAlpha(255);

 public enum Style {
 /**
  * Geometry and text drawn with this style will be filled, ignoring all
  * stroke-related settings in the paint.
  */
 FILL  (0),
 /**
  * Geometry and text drawn with this style will be stroked, respecting
  * the stroke-related fields on the paint.
  */
 STROKE  (1),
 /**
  * Geometry and text drawn with this style will be both filled and
  * stroked at the same time, respecting the stroke-related fields on
  * the paint. This mode can give unexpected results if the geometry
  * is oriented counter-clockwise. This restriction does not apply to
  * either FILL or STROKE.
  */
 FILL_AND_STROKE (2);

 Style(int nativeInt) {
  this.nativeInt = nativeInt;
 }
 final int nativeInt;
 }

mPaint.setStrokeWidth(50);

 /**
 * The Cap specifies the treatment for the beginning and ending of
 * stroked lines and paths. The default is BUTT.
 */
 public enum Cap {
 /**
  * The stroke ends with the path, and does not project beyond it.
  */
 BUTT (0),
 /**
  * The stroke projects out as a semicircle, with the center at the
  * end of the path.
  */
 ROUND (1),
 /**
  * The stroke projects out as a square, with the center at the end
  * of the path.
  */
 SQUARE (2);

 private Cap(int nativeInt) {
  this.nativeInt = nativeInt;
 }
 final int nativeInt;
 }

 @Override
 protected void onDraw(Canvas canvas) {
 super.onDraw(canvas);
 mPaint.setColor(Color.BLUE);
 mPaint.setAlpha(255);

 //设置画笔的样式
 mPaint.setStyle(Paint.Style.FILL_AND_STROKE);
 //画笔的宽度
 mPaint.setStrokeWidth(50);
 mPaint.setStrokeCap(Paint.Cap.SQUARE);//方形
 mPaint.setStrokeJoin(Paint.Join.BEVEL);//直线

 Path path = new Path();
 path.moveTo(100, 100);
 path.lineTo(300, 100);
 canvas.drawPath(path, mPaint);

 mPaint.reset();//重置
 mPaint.setColor(Color.RED);
 mPaint.setStyle(Paint.Style.FILL_AND_STROKE);
 mPaint.setStrokeWidth(50);
 mPaint.setStrokeCap(Paint.Cap.ROUND);//圆形
 mPaint.setStrokeJoin(Paint.Join.BEVEL);//直线

 Path path1 = new Path();
 path1.moveTo(100, 200);
 path1.lineTo(300, 200);
 canvas.drawPath(path1, mPaint);

 mPaint.reset();//重置
 mPaint.setColor(Color.GREEN);
 mPaint.setStyle(Paint.Style.FILL_AND_STROKE);
 mPaint.setStrokeWidth(50);
 mPaint.setStrokeCap(Paint.Cap.BUTT);//没有
 mPaint.setStrokeJoin(Paint.Join.BEVEL);//直线

 Path path2 = new Path();
 path2.moveTo(100, 300);
 path2.lineTo(300, 300);
 canvas.drawPath(path2, mPaint);

 }

 @Override
 protected void onDraw(Canvas canvas) {
 super.onDraw(canvas);
 mPaint.setColor(Color.BLUE);
 mPaint.setAlpha(255);
 mPaint.setStyle(Paint.Style.STROKE);//设置画笔的样式
 mPaint.setStrokeWidth(50);//画笔的宽度
 mPaint.setStrokeCap(Paint.Cap.BUTT);//线帽
 mPaint.setStrokeJoin(Paint.Join.BEVEL);

 Path path = new Path();
 path.moveTo(100, 100);
 path.lineTo(300, 100);
 path.lineTo(100, 300);
 path.close();
 canvas.drawPath(path, mPaint);

 mPaint.reset();//重置
 mPaint.setColor(Color.RED);
 mPaint.setStyle(Paint.Style.FILL_AND_STROKE);
 mPaint.setStrokeWidth(50);
 mPaint.setStrokeCap(Paint.Cap.BUTT);//圆形
 mPaint.setStrokeJoin(Paint.Join.ROUND);//圆弧

 Path path1 = new Path();
 path1.moveTo(100, 400);
 path1.lineTo(300, 400);
 path1.lineTo(100, 700);
 path1.close();
 canvas.drawPath(path1, mPaint);

 mPaint.reset();//重置
 mPaint.setColor(Color.GREEN);
 mPaint.setStyle(Paint.Style.FILL_AND_STROKE);
 mPaint.setStrokeWidth(50);
 mPaint.setStrokeCap(Paint.Cap.BUTT);//没有
 mPaint.setStrokeJoin(Paint.Join.MITER);//锐角

 Path path2 = new Path();
 path2.moveTo(100, 800);
 path2.lineTo(300, 800);
 path2.lineTo(100, 1100);
 path2.close();
 canvas.drawPath(path2, mPaint);

 }

mPaint.setAntiAlias(true);

setLetterSpacing

mPaint.setStrikeThruText(true);

mPaint.setUnderlineText(true);

mPaint.setTextSize(textSize);

mPaint.setTypeface(Typeface.BOLD);
// Style
public static final int NORMAL = 0;//常规
public static final int BOLD = 1;//粗体
public static final int ITALIC = 2; //斜体
public static final int BOLD_ITALIC = 3;//粗斜体

Typeface.create(familyName, style)

mPaint.setTextSkewX(-0.25f);

mPaint.setTextAlign(Align.LEFT)

public enum Align {
  /**
   * The text is drawn to the right of the x,y origin
   */
  LEFT (0),//左对齐
  /**
   * The text is drawn centered horizontally on the x,y origin
   */
  CENTER (1),//居中
  /**
   * The text is drawn to the left of the x,y origin
   */
  RIGHT (2);//右对齐

  private Align(int nativeInt) {
   this.nativeInt = nativeInt;
  }
  final int nativeInt;
 }

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

Rect bounds获取文本的矩形区域（宽高）
mPaint.getTextBounds(text, index, count, bounds)
mPaint.getTextBounds(text, start, end, bounds)
  
//获取文本的宽度，和上面类似，但是是一个比较粗略的结果
float measureText = mPaint.measureText(str);
//获取文本的宽度，和上面类似，但是是比较精准的。
float[] measuredWidth = new float[10];

//measuredWidth得到每一个字符的宽度；textWidths字符数
int textWidths = mPaint.getTextWidths(str, measuredWidth);
mPaint.getTextWidths(text, start, end, widths)

public class PaintView extends View {

 private Paint mPaint;
 private String text = "你是我世界之光，我心另一半";

 public PaintView(Context context) {
  this(context,null);
 }

 public PaintView(Context context, @Nullable AttributeSet attrs) {
  this(context, attrs,0);
 }

 public PaintView(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
  super(context, attrs, defStyleAttr);
  init(context, attrs, defStyleAttr);
 }

 private void init(Context context, AttributeSet attrs, int defStyleAttr) {
  mPaint = new Paint();
 }


 @Override
 protected void onDraw(Canvas canvas) {
  super.onDraw(canvas);
  mPaint.setColor(Color.BLUE);
  mPaint.setStyle(Paint.Style.STROKE);//设置画笔的样式
  mPaint.setStrokeCap(Paint.Cap.BUTT);//线帽
  mPaint.setStrokeJoin(Paint.Join.BEVEL);

  int top = 100;
  int baselineX = 0;
  mPaint.setTextSize(50);
  mPaint.setTextAlign(Paint.Align.LEFT);

  canvas.drawLine(0, top, 2000, top, mPaint);


  //文本Metrics
  Paint.FontMetrics fontMetrics = mPaint.getFontMetrics();
  float baselineY = top - fontMetrics.top;
  canvas.drawText(text, baselineX, baselineY, mPaint);

 }
}

@Override
 protected void onDraw(Canvas canvas) {
  super.onDraw(canvas);

  int x = getPaddingLeft();

  //dy 代表的是：高度的一半到 baseLine的距离
  Paint.FontMetricsInt fontMetrics = paint.getFontMetricsInt();
  // top 是一个负值 bottom 是一个正值 top，bttom的值代表是 bottom是baseLine到文字底部的距离（正值）
  // 必须要清楚的，可以自己打印就好
  int dy = (fontMetrics.bottom - fontMetrics.top)/2 - fontMetrics.bottom;
  int baseLine = getHeight()/2 + dy;

  canvas.drawText(costom_text,x,baseLine,paint);
 }

/**
  * 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) {
  native_drawText(mNativeCanvasWrapper, text, 0, text.length(), x, y, paint.mBidiFlags,
    paint.getNativeInstance(), paint.mNativeTypeface);
 }

int dy = (fontMetrics.bottom - fontMetrics.top)/2 - fontMetrics.bottom;

int baseLine = getHeight()/2 + dy;