DIP转化为PX

系统自带的DIP转化为PX方法：

int height = (int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, 50, this.getResources().getDisplayMetrics());

applyDimension的源码：

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;
    }

第三个是默认的metrics值，常取this.getResources().getDisplayMetrics();