Android(安卓)各尺寸单位间的换算

~android-sdk\sources\android-17\android\util\TypedValue.java 中的函数：

/**

* Converts an unpacked complex data value holding a dimension to its final floating
* point value. The two parameters <var>unit</var> and <var>value</var>
* are as in {@link #TYPE_DIMENSION}.
*
* @param unit The unit to convert from.
* @param value The value to apply the unit to.
* @param metrics Current display metrics to use in the conversion --
* supplies display density and scaling information.
*
* @return The complex floating point value multiplied by the appropriate
* metrics depending on its unit.
*/
public static float applyDimension(int unit, float value,
DisplayMetrics metrics)
{
switch (unit) {
//Value is raw pixels.
case COMPLEX_UNIT_PX:
return value;
//Value is Device Independent Pixels.
case COMPLEX_UNIT_DIP:
return value * metrics.density;
//Value is a scaled pixel.
case COMPLEX_UNIT_SP:
return value * metrics.scaledDensity;
//Value is in points.
case COMPLEX_UNIT_PT:
return value * metrics.xdpi * (1.0f/72);
//Value is in inches.
case COMPLEX_UNIT_IN:
return value * metrics.xdpi;
//Value is in millimeters.
case COMPLEX_UNIT_MM:
return value * metrics.xdpi * (1.0f/25.4f);
}
return 0;
}

~android-sdk\sources\android-17\android\util\DisplayMetrics.java 中的一些定义：

/**
* Standard quantized DPI for medium-density screens.
*/
public static final int DENSITY_MEDIUM = 160;
/**
* The reference density used throughout the system.
*/
public static final int DENSITY_DEFAULT = DENSITY_MEDIUM;
/**
* 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;
//默认值 density = DENSITY_DEVICE / (float) DENSITY_DEFAULT;

/**
* A scaling factor for fonts displayed on the display. This is the same
* as {@link #density}, except that it may be adjusted in smaller
* increments at runtime based on a user preference for the font size.
*/
public float scaledDensity;
//默认值 scaledDensity = density;

/**The exact physical pixels per inch of the screen in the X dimension.
*/
public float xdpi;
//默认值xdpi = DENSITY_DEVICE;

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