Android全面屏最大纵横比适配

遇到的问题

在项目开发中遇到屏幕底部或顶部出现了黑条，页面没有全部占满屏幕，情况如下：

解决方案

影响因素：
1 项目 targetSdkVerion 值
2 项目是否支持分屏模式：
如果设置了android:resizeableActivity=“true”，则代表支持分屏模式。（此设置只针对Activity有效）

设置最大纵横比方法：
方法一：在AndroidManifest.xml中节点下做如下配置即可：

<meta-dataandroid:name="android.max_aspect"android:value="ratio_float"/>

其中ratio_float为浮点数，官方建议为2.1或更大，因为18.5：9=2.055555555……，如果日后出现纵横比更大的手机，此值将需要设为更大。

方法二：max_aspect值也可以在Java代码中动态地设置，通过下面的方法即可实现：

public void setMaxAspect() {ApplicationInfo applicationInfo = null;try {applicationInfo = getPackageManager().getApplicationInfo(getPackageName(), PackageManager.GET_META_DATA);} catch (PackageManager.NameNotFoundException e) {e.printStackTrace();}if(applicationInfo == null){throw new IllegalArgumentException(" get application info = null, has no meta data! ");}applicationInfo.metaData.putString("android.max_aspect", "2.1");}

场景1：
targetSdkVerion >= 26或者支持分屏模式，删除最大纵横比设置：
删除最大纵横比方法：删除android:name="android.max_aspect"即可，Android会自动根据屏幕调节（推荐）
场景2：
targetSdkVerion >= 26且不支持分屏模式时，删除最大纵横比设置或者将其设置为最大值：
（1）删除最大纵横比方法：删除android:name="android.max_aspect"即可，Android会自动根据屏幕调节（推荐）
（2）设置最大纵横比

<meta-dataandroid:name="android.max_aspect"android:value="2.4"/>

场景三：
targetSdkVerion <= 25且不支持分屏模式时（android:resizeableActivity API 级别 24 添加的，如果应用面向 API 级别 24 或更高级别，但未对该属性指定值，则该属性的值默认设为 true）：
默认的apsect ratio为1.86，必须对最大纵横比进行设置，否则在大于1.86的手机上运行App会出现黑条的现象。

<meta-dataandroid:name="android.max_aspect"android:value="2.4"/>

解释下什么是最大屏幕纵横比

理解：
当Activity设置了分屏模式：android:resizeableActivity=“true”，则maxAspectRatio属性将失效（即"android.max_aspect"属性将不起作用）

原理：

// 解析activity时候如设置了maxAspectRatio就将设置好的传输进去。private Activity parseActivity(Package owner, Resources res,XmlResourceParser parser, int flags, String[] outError, CachedComponentArgs cachedArgs,boolean receiver, boolean hardwareAccelerated)throws XmlPullParserException, IOException {if (sa.hasValue(R.styleable.AndroidManifestActivity_maxAspectRatio)&& sa.getType(R.styleable.AndroidManifestActivity_maxAspectRatio)== TypedValue.TYPE_FLOAT) {a.setMaxAspectRatio(sa.getFloat(R.styleable.AndroidManifestActivity_maxAspectRatio,0 /*default*/));}....
//接着看一下setMaxAspectRatio，先判断是否可以resize,也就是前面的android:resizeableActivity="false"。
private void setMaxAspectRatio(float maxAspectRatio) {if (info.resizeMode == RESIZE_MODE_RESIZEABLE|| info.resizeMode == RESIZE_MODE_RESIZEABLE_VIA_SDK_VERSION) {// Resizeable activities can be put in any aspect ratio.return;}if (maxAspectRatio < 1.0f && maxAspectRatio != 0) {// Ignore any value lesser than 1.0.return;}info.maxAspectRatio = maxAspectRatio;mHasMaxAspectRatio = true;}//如果没有该属性 再设置默认的。private static final float DEFAULT_PRE_O_MAX_ASPECT_RATIO = 1.86f;..../*** Sets every the max aspect ratio of every child activity that doesn't already have an aspect* ratio set.*/private void setMaxAspectRatio(Package owner) {// Default to (1.86) 16.7:9 aspect ratio for pre-O apps and unset for O and greater.// NOTE: 16.7:9 was the max aspect ratio Android devices can support pre-O per the CDD.float maxAspectRatio = owner.applicationInfo.targetSdkVersion < O? DEFAULT_PRE_O_MAX_ASPECT_RATIO : 0;//android o 之前的用默认1.86，之后的就根据手机；屏幕。if (owner.applicationInfo.maxAspectRatio != 0) {// Use the application max aspect ration as default if set.maxAspectRatio = owner.applicationInfo.maxAspectRatio;} else if (owner.mAppMetaData != null&& owner.mAppMetaData.containsKey(METADATA_MAX_ASPECT_RATIO)) {maxAspectRatio = owner.mAppMetaData.getFloat(METADATA_MAX_ASPECT_RATIO, maxAspectRatio);}for (Activity activity : owner.activities) {// If the max aspect ratio for the activity has already been set, skip.if (activity.hasMaxAspectRatio()) {continue;//如果activity已经有这个属性了就不在重新设置，如果没有在设置一个默认的。}// By default we prefer to use a values defined on the activity directly than values// defined on the application. We do not check the styled attributes on the activity// as it would have already been set when we processed the activity. We wait to process// the meta data here since this method is called at the end of processing the// application and all meta data is guaranteed.final float activityAspectRatio = activity.metaData != null? activity.metaData.getFloat(METADATA_MAX_ASPECT_RATIO, maxAspectRatio): maxAspectRatio;activity.setMaxAspectRatio(activityAspectRatio);}}

// frameworks/base/services/core/java/com/android/server/am/ActivityRecord.java
/*** Computes the bounds to fit the Activity within the bounds of the {@link Configuration}.*/// TODO(b/36505427): Consider moving this method and similar ones to ConfigurationContainer.private void computeBounds(Rect outBounds) {outBounds.setEmpty();final float maxAspectRatio = info.maxAspectRatio;final ActivityStack stack = getStack();if (task == null || stack == null || !task.mFullscreen || maxAspectRatio == 0|| isInVrUiMode(getConfiguration())) {// We don't set override configuration if that activity task isn't fullscreen. I.e. the// activity is in multi-window mode. Or, there isn't a max aspect ratio specified for// the activity. This is indicated by an empty {@link outBounds}. We also don't set it// if we are in VR mode.return;//如果是0直接就pass了没有后面计算过程了。}...