闲谈自定义控件源码-view 坐标

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#自定义控件 #view #坐标

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本文解析了Android中Density与DensityDPI的概念及其区别，并详细介绍了View如何通过left、top、right、bottom进行定位。

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自定义view中尤其是Ondraw和做动画的时候，基本上都在和坐标打交道

一、2个概念的区分 density densitydpi

区分两个概念

首先可以看一个类 DisplayMetrics Display：显示展示的意思 Metrics：度量。可见这是一个关于屏幕度量的类

density和densityDpi是该类的两个成员变量

 /**
     * The logical density of the display.  This is a scaling factor for the
     * Density Independent Pixel unit, where one DIP is one pixel on an
     * approximately 160 dpi screen (for example a 240x320, 1.5"x2" screen), 
     * providing the baseline of the system's display. Thus on a 160dpi screen 
     * this density value will be 1; on a 120 dpi screen it would be .75; etc.
     *  
     * <p>This value does not exactly follow the real screen size (as given by 
     * {@link #xdpi} and {@link #ydpi}, but rather is used to scale the size of
     * the overall UI in steps based on gross changes in the display dpi.  For 
     * example, a 240x320 screen will have a density of 1 even if its width is 
     * 1.8", 1.3", etc. However, if the screen resolution is increased to 
     * 320x480 but the screen size remained 1.5"x2" then the density would be 
     * increased (probably to 1.5).
     *
     * @see #DENSITY_DEFAULT
     */
    public float density;
    /**
     * The screen density expressed as dots-per-inch.  May be either
     * {@link #DENSITY_LOW}, {@link #DENSITY_MEDIUM}, or {@link #DENSITY_HIGH}.
     */
    public int densityDpi;