Android N Display Size
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Android N新特性-屏幕缩放
Android 7.0 支持用户设置显示尺寸,以放大或缩小屏幕上的所有元素,从而提升设备对视力不佳用户的可访问性。用户无法将屏幕缩放至低于最小屏幕宽度 sw320dp,该宽度是 Nexus 4 的宽度,也是常规中等大小手机的宽度。
当设备密度发生更改时,系统会以如下方式通知正在运行的应用:
如果是面向 API 级别 23 或更低版本系统的应用,系统会自动终止其所有后台进程。这意味着如果用户切换离开此类应用,转而打开 Settings 屏幕并更改 Display size 设置,则系统会像处理内存不足的情况一样终止该应用。如果应用具有任何前台进程,则系统会如处理运行时更改中所述将配置变更通知给这些进程,就像对待设备屏幕方向变更一样。
如果是面向 Android 7.0 的应用,则其所有进程(前台和后台)都会收到有关配置变更的通知,如处理运行时更改中所述。
大多数应用并不需要进行任何更改即可支持此功能,不过前提是这些应用遵循 Android 最佳做法。具体要检查的事项:
- 在屏幕宽度为 sw320dp 的设备上测试您的应用,并确保其充分运行。
- 当设备配置发生变更时,更新任何与密度相关的缓存信息,例如缓存位图或从网络加载的资源。当应用从暂停状态恢复运行时,检查配置变更。
注:如果您要缓存与配置相关的数据,则最好也包括相关元数据,例如该数据对应的屏幕尺寸或像素密度。保存这些元数据便于您在配置变更后决定是否需要刷新缓存数据。 - 避免用像素单位指定尺寸,因为像素不会随屏幕密度缩放。应改为使用与密度无关像素 (dp) 单位指定尺寸
Dpi,dp,ppi,sp,in&px参考
Android屏幕适配全攻略
Display Size分析
Display Size 对应手机的Settings->Display->Display size。用来缩放手机屏幕。
流程分析
1. screen_zoom_activity.xml
Display Size调整设置项对应的布局文件,通过seekbar来显示缩放等级,通过按钮来调整等级
2. CustomPreviewSeekBarPreferenceFragment.java
final int max = Math.max(1, mEntries.length - 1);final LabeledSeekBar seekBar = (LabeledSeekBar) content.findViewById(R.id.seek_bar);seekBar.setLabels(mEntries);seekBar.setMax(max);seekBar.setProgress(mInitialIndex);
mEntries数组长度决定了缩放调整的级数,数组内容为每个等级的标签,mInitialIndex决定了当前所在的级数,第一次获取的则为默认等级。
3. ScreenZoomSettings.java
该类继承自PreviewSeekBarPreferenceFragment.java,该类确定了mEntries和mInitialIndex的值。这两个值都是由DisplayDensityUtils对象获得。
4. DisplayDensityUtils.java
mEntries和mInitialIndex可以看到是通过DisplayDensityUtils的getEntries()和getCurrentIndex()方法获得。而该方法中返回值搜索代码即可看到是在该类的构造方法中确定。
源码如下
public class DisplayDensityUtils { /** Minimum increment between density scales. */ private static final float MIN_SCALE_INTERVAL = 0.09f; /** Minimum density scale. This is available on all devices. */ private static final float MIN_SCALE = 0.85f; /** Maximum density scale. The actual scale used depends on the device. */ private static final float MAX_SCALE = 1.50f; /** Summary used for "default" scale. */ public static final int SUMMARY_DEFAULT = R.string.screen_zoom_summary_default; /** Summary used for "custom" scale. */ private static final int SUMMARY_CUSTOM = R.string.screen_zoom_summary_custom; /** * Summaries for scales smaller than "default" in order of smallest to * largest. */ private static final int[] SUMMARIES_SMALLER = new int[] { R.string.screen_zoom_summary_small }; /** * Summaries for scales larger than "default" in order of smallest to * largest. */ private static final int[] SUMMARIES_LARGER = new int[] { R.string.screen_zoom_summary_large, R.string.screen_zoom_summary_very_large, R.string.screen_zoom_summary_extremely_large, }; /** * Minimum allowed screen dimension, corresponds to resource qualifiers * "small" or "sw320dp". This value must be at least the minimum screen * size required by the CDD so that we meet developer expectations. */ private static final int MIN_DIMENSION_DP = 320; private final String[] mEntries; private final int[] mValues; private final int mDefaultDensity; private final int mCurrentIndex; public DisplayDensityUtils(Context context) { final int defaultDensity = DisplayDensityUtils.getDefaultDisplayDensity( Display.DEFAULT_DISPLAY); if (defaultDensity <= 0) { mEntries = null; mValues = null; mDefaultDensity = 0; mCurrentIndex = -1; return; } final Resources res = context.getResources(); final DisplayMetrics metrics = res.getDisplayMetrics(); final int currentDensity = metrics.densityDpi; int currentDensityIndex = -1; // Compute number of "larger" and "smaller" scales for this display. final int minDimensionPx = Math.min(metrics.widthPixels, metrics.heightPixels); final int maxDensity = DisplayMetrics.DENSITY_MEDIUM * minDimensionPx / MIN_DIMENSION_DP; final float maxScale = Math.min(MAX_SCALE, maxDensity / (float) defaultDensity); final float minScale = MIN_SCALE; final int numLarger = (int) MathUtils.constrain((maxScale - 1) / MIN_SCALE_INTERVAL, 0, SUMMARIES_LARGER.length); final int numSmaller = (int) MathUtils.constrain((1 - minScale) / MIN_SCALE_INTERVAL, 0, SUMMARIES_SMALLER.length); String[] entries = new String[1 + numSmaller + numLarger]; int[] values = new int[entries.length]; int curIndex = 0; if (numSmaller > 0) { final float interval = (1 - minScale) / numSmaller; for (int i = numSmaller - 1; i >= 0; i--) { // Round down to a multiple of 2 by truncating the low bit. final int density = ((int) (defaultDensity * (1 - (i + 1) * interval))) & ~1; if (currentDensity == density) { currentDensityIndex = curIndex; } entries[curIndex] = res.getString(SUMMARIES_SMALLER[i]); values[curIndex] = density; curIndex++; } } if (currentDensity == defaultDensity) { currentDensityIndex = curIndex; } values[curIndex] = defaultDensity; entries[curIndex] = res.getString(SUMMARY_DEFAULT); curIndex++; if (numLarger > 0) { final float interval = (maxScale - 1) / numLarger; for (int i = 0; i < numLarger; i++) { // Round down to a multiple of 2 by truncating the low bit. final int density = ((int) (defaultDensity * (1 + (i + 1) * interval))) & ~1; if (currentDensity == density) { currentDensityIndex = curIndex; } values[curIndex] = density; entries[curIndex] = res.getString(SUMMARIES_LARGER[i]); curIndex++; } } final int displayIndex; if (currentDensityIndex >= 0) { displayIndex = currentDensityIndex; } else { // We don't understand the current density. Must have been set by // someone else. Make room for another entry... int newLength = values.length + 1; values = Arrays.copyOf(values, newLength); values[curIndex] = currentDensity; entries = Arrays.copyOf(entries, newLength); entries[curIndex] = res.getString(SUMMARY_CUSTOM, currentDensity); displayIndex = curIndex; } mDefaultDensity = defaultDensity; mCurrentIndex = displayIndex; mEntries = entries; mValues = values; } public String[] getEntries() { return mEntries; } public int getCurrentIndex() { return mCurrentIndex; }}
构造函数首先根据默认DPI来计算可缩放的等级数->填充smaller的mEntries标签内容->设置默认密度等级的下标和填充标签->填充larger的mEntries的标签内容
计算等级数
final int minDimensionPx = Math.min(metrics.widthPixels, metrics.heightPixels);final int maxDensity = DisplayMetrics.DENSITY_MEDIUM * minDimensionPx / MIN_DIMENSION_DP;final float maxScale = Math.min(MAX_SCALE, maxDensity / (float) defaultDensity);final float minScale = MIN_SCALE;final int numLarger = (int) MathUtils.constrain((maxScale - 1) / MIN_SCALE_INTERVAL, 0, SUMMARIES_LARGER.length);final int numSmaller = (int) MathUtils.constrain((1 - minScale) / MIN_SCALE_INTERVAL, 0, SUMMARIES_SMALLER.length);String[] entries = new String[1 + numSmaller + numLarger];
defaultDensity是通过 DisplayDensityUtils.getDefaultDisplayDensity(Display.DEFAULT_DISPLAY)获取,该默认密度对应代码中ro.sf.lcd_density
numSmaller为最小为0,最大为1,此处值为1
numLarger则为0到3之间,具体取决于maxScale,它又取决于 maxDensity / (float) defaultDensity
此处以测试机5015为例,其ro.sf.lcd_density默认为240dpi,width为480px,height为854px则defaultDensity为240 maxDensity = DisplayMetrics.DENSITY_MEDIUM * minDimensionPx / MIN_DIMENSION_DP ==>160*480/320 =240则maxScale = 240/240 = 1则numLarger = 0
修改Android DPI 代码路径:alps/device/sagetel/sr6580_we_n/system.prop,ro.sf.lcd_density修改该值则修改了手机的默认密度
填充smaller
设置默认密度
if (currentDensity == defaultDensity) { currentDensityIndex = curIndex;//设置默认下标}values[curIndex] = defaultDensity;entries[curIndex] = res.getString(SUMMARY_DEFAULT);填充默认等级的描述
填充larger
等级客制化
可通过修改ro.sf.lcd_density值来改变缩放等级数,density越小,等级数越多,但最大5级。为了界面显示正常,我们需调整合适的density,density测试可通过
修改屏幕Dpiadb shell wm density 240 //修改屏幕密度为240dpiadb shell wm density reset //重置屏幕密度为默认密度
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