Android(安卓)中dp 和px 转换及原理分析
16lz
2021-01-26
具体的转换方法如下,网上都是有的,但是自己看了之后感觉还是有点不明不白的,具体为什么呢,可以继续看后面.
/** * 根据手机的分辨率从 dp 的单位 转成为 px(像素) */public static int dip2px(Context context, float dpValue) {final float scale = context.getResources().getDisplayMetrics().density;return (int) (dpValue * scale + 0.5f);}/** * 根据手机的分辨率从 px(像素) 的单位 转成为 dp */public static int px2dip(Context context, float pxValue) {final float scale = context.getResources().getDisplayMetrics().density;return (int) (pxValue / scale + 0.5f);}
首先先列出来相关的方法:
Resources.java
public Resources(AssetManager assets, DisplayMetrics metrics, Configuration config, CompatibilityInfo compInfo) { mAssets = assets; mMetrics.setToDefaults(); mCompatibilityInfo = compInfo; updateConfiguration(config, metrics); assets.ensureStringBlocks();}
DisplayMetrics.java 相关方法
public void setToDefaults() { widthPixels = 0; heightPixels = 0; density = DENSITY_DEVICE / (float) DENSITY_DEFAULT; densityDpi = DENSITY_DEVICE; scaledDensity = density; xdpi = DENSITY_DEVICE; ydpi = DENSITY_DEVICE; noncompatWidthPixels = widthPixels; noncompatHeightPixels = heightPixels; noncompatDensity = density; noncompatDensityDpi = densityDpi; noncompatScaledDensity = scaledDensity; noncompatXdpi = xdpi; noncompatYdpi = ydpi; } public static int DENSITY_DEVICE = getDeviceDensity(); private static int getDeviceDensity() { // qemu.sf.lcd_density can be used to override ro.sf.lcd_density // when running in the emulator, allowing for dynamic configurations. // The reason for this is that ro.sf.lcd_density is write-once and is // set by the init process when it parses build.prop before anything else. return SystemProperties.getInt("qemu.sf.lcd_density", SystemProperties.getInt("ro.sf.lcd_density", DENSITY_DEFAULT)); }/** * The reference density used throughout the system. */ public static final int DENSITY_DEFAULT = DENSITY_MEDIUM;/** * Standard quantized DPI for medium-density screens. */ public static final int DENSITY_MEDIUM = 160;
在 Resources.java 的构造函数里面调用DisplayMetrics 的setToDefaults 方法,使density 取值为DENSITY_DEVICE / (float) DENSITY_DEFAULT;
使density 最终的值和key:qemu.sf.lcd_density 和default_value:ro.sf.lcd_density 有关系,
系统里面一般并没有额外对key:qemu.sf.lcd_density 赋值,故取值ro.sf.lcd_density,而ro.sf.lcd_density 的值一般是在系统源码里面的设置好的了,比如:system.prop 里面可以设置该值.
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