android dp(裝置獨立像素) sp(可縮放像素) pt(磅) in(英尺) mm(毫米) 轉換為 px(像素)

android單位換算，網路有很多相關轉碼。但是，我推薦使用使用官方的轉換方法：TypedValue.applyDimension。

    /**
     * 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;
    }

 

看到官方的轉換方法後，有些人會問為什麼網路的轉換方法後面加了0.5?

加0.5的原因是保證傳回值大於0。我們從TypedValue.complexToDimensionPixelSize方法得到印證。

    /**
     * Converts a complex data value holding a dimension to its final value
     * as an integer pixel size.  This is the same as
     * {@link #complexToDimension}, except the raw floating point value is
     * converted to an integer (pixel) value for use as a size.  A size
     * conversion involves rounding the base value, and ensuring that a
     * non-zero base value is at least one pixel in size.
     * The given <var>data</var> must be structured as a
     * {@link #TYPE_DIMENSION}.
     *  
     * @param data A complex data value holding a unit, magnitude, and
     *             mantissa.
     * @param metrics Current display metrics to use in the conversion --
     *                supplies display density and scaling information.
     *
     * @return The number of pixels specified by the data and its desired
     * multiplier and units.
     */
    public static int complexToDimensionPixelSize(int data,
            DisplayMetrics metrics)
    {
        final float value = complexToFloat(data);
        final float f = applyDimension(
                (data>>COMPLEX_UNIT_SHIFT)&COMPLEX_UNIT_MASK,
                value,
                metrics);
        final int res = (int)(f+0.5f);
        if (res != 0) return res;
        if (value == 0) return 0;
        if (value > 0) return 1;
        return -1;
    }