android 单位之间的换算 TypedValue 我们知道 TypedValue 中有个applyDimension(int unit, float value, DisplayMetricsmetrics) 方法，通过这个方法可以将各种单位装换成像素，现在就来看看这个方法是如何实现的，也就知道了他们之间的转换关系，首先看源码：

gistfile1.java

 /**
     * 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) {
        case COMPLEX_UNIT_PX:
            return value;
        case COMPLEX_UNIT_DIP:
            return value * metrics.density;
        case COMPLEX_UNIT_SP:
            return value * metrics.scaledDensity;
        case COMPLEX_UNIT_PT:
            return value * metrics.xdpi * (1.0f/72);
        case COMPLEX_UNIT_IN:
            return value * metrics.xdpi;
        case COMPLEX_UNIT_MM:
            return value * metrics.xdpi * (1.0f/25.4f);
        }
        return 0;
    }

以dip为例，他们的转换关系显而易见：px = dip * 密度（metrics.density）