自定义View的一些积累

• 测量方法 onMeasure()

protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) 

返回的参数是32位，高两位是测量模式。后30位是尺寸

private static final int MODE_SHIFT = 30;
/**
* 这个模式，我也不知道他干嘛的，只要在xml里设置了，高两位都不会是00。至于没有设置的情况。。。。这个还真的不知道哦
* Measure specification mode: The parent has not imposed any constraint
* on the child. It can be whatever size it wants.
*/
public static final int UNSPECIFIED = 0 << MODE_SHIFT;

/**
 * 精准模式，如果当match_parent和一个固定的尺寸时，返回。
 * 这个模式下。子控件的大小是充满父布局，或者在自己想要的尺 * 寸下。子控件的大小收到父控件的影响
 * Measure specification mode: The parent has determined an exact size
 * for the child. The child is going to be given those bounds regardless
 * of how big it wants to be.
 */
public static final int EXACTLY     = 1 << MODE_SHIFT;

/**
 *如果是wrap_content
 *这个模式下，控件的大小是尽可能的去得到自己的大小。根据控件内容自填充。
 * Measure specification mode: The child can be as large as it wants up
 * to the specified size.
 */
public static final int AT_MOST     = 2 << MODE_SHIFT;

这个方法是用来测量控件尺寸的。

 // 返回的mode是32位int。后30位是0。
 int mode = MeasureSpec.getMode(measureSpec);
 int size = MeasureSpec.getSize(measureSpec);
 
 获取到测量模式和尺寸， 
        

• 绘制View onDraw()

protected void onDraw(Canvas canvas)

通过这个方法来绘制view，通过画布Canvas和画笔Paint共同绘制。

一些Paint的设置

Paint

• setAnitAlias(boolean aa)

去画笔锯齿

• setStyle(Style style)

画笔的样式

public enum Style {
        /**
         * 将充满
         * Geometry and text drawn with this style will be filled, ignoring all
         * stroke-related settings in the paint.
         */
        FILL            (0),
        /** 绘制空心的状态
         * 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;
    }

• setDither(boolean dither)

  图片设置抖动处理

• setColor(int color);

  设置画笔的颜色

• setStrokeWidth(float width)

  设置线条的宽度

mPaint = new Paint();
        // 设置颜色
        mPaint.setColor(Color.BLUE);
        // 设置填充状态
        mPaint.setStyle(Paint.Style.STROKE);
        // 设置线条宽度
        mPaint.setStrokeWidth(3);
        // 去锯齿
        mPaint.setAntiAlias(true);

微信截图_20191011233116.png