Android中dp,px,sp等單位轉換

一般我們都會自己寫一個dp轉px或者sp轉px的工具類，給個鏈接http://blog.csdn.net/top_code/article/details/8588703
但是今天我發現Android自帶了這種轉換工具類TypedValue，下面是轉換的方法

    /**
     * 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;
    }

可以看出，這個方法不僅支持dp轉px，sp轉px，還有不常用的pt、in等單位的轉換。只是不懂爲啥網上自己做轉換時都要+0.5f，意思是想向上取整，但是意義何在呢？

---

注意，在代碼中設置TextView字體大小時不需要進行轉換：

    /**
     * Set the default text size to the given value, interpreted as "scaled
     * pixel" units.  This size is adjusted based on the current density and
     * user font size preference.
     *
     * @param size The scaled pixel size.
     *
     * @attr ref android.R.styleable#TextView_textSize
     */
    @android.view.RemotableViewMethod
    public void setTextSize(float size) {
        setTextSize(TypedValue.COMPLEX_UNIT_SP, size);
    }

    /**
     * Set the default text size to a given unit and value.  See {@link
     * TypedValue} for the possible dimension units.
     *
     * @param unit The desired dimension unit.
     * @param size The desired size in the given units.
     *
     * @attr ref android.R.styleable#TextView_textSize
     */
    public void setTextSize(int unit, float size) {
        Context c = getContext();
        Resources r;

        if (c == null)
            r = Resources.getSystem();
        else
            r = c.getResources();

        setRawTextSize(TypedValue.applyDimension(
            unit, size, r.getDisplayMetrics()));
    }

可以看出，直接設置以sp爲單位的字體大小就OK。