需求：获取当前的 Activity 对象，Activity 是系统创建的，一种方法：在 onCreate 的时候拿到引用，这样就得修改 onCreate 方法，还得维护一个数组去管理 Activity 的引用。第二种方法：通过反射拿到 ActivityThread 中的 mActivities 属性，进而拿到当前的 activity 对象（ paused 为 false 的activity）。
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| public static Activity getActivity() {
try {
Class activityThreadClass = Class.forName("android.app.ActivityThread");
Object activityThread = activityThreadClass.getMethod("currentActivityThread").invoke(null);
Field activitiesField = activityThreadClass.getDeclaredField("mActivities");
activitiesField.setAccessible(true);
Map activities = null;
if (Build.VERSION.SDK_INT < Build.VERSION_CODES.KITKAT) { // 4.4 以下使用的是 HashMap
activities = (HashMap) activitiesField.get(activityThread);
}else{ // 4.4 以上使用的是 ArrayMap
activities = (ArrayMap) activitiesField.get(activityThread);
}
for (Object activityRecord : activities.values()) {
Class activityRecordClass = activityRecord.getClass();
Field pausedField = activityRecordClass.getDeclaredField("paused"); // 找到 paused 为 false 的activity
pausedField.setAccessible(true);
if (!pausedField.getBoolean(activityRecord)) {
Field activityField = activityRecordClass.getDeclaredField("activity");
activityField.setAccessible(true);
Activity activity = (Activity) activityField.get(activityRecord);
return activity;
}
}
} catch (Exception e) {
e.printStackTrace();
}
return null;
}
|
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