public void setFilterTouchesWhenObscured(boolean enabled) {
    setFlags(enabled ? FILTER_TOUCHES_WHEN_OBSCURED : 0,
            FILTER_TOUCHES_WHEN_OBSCURED);
}

@SuppressWarnings("WeakerAccess") /* synthetic access */
final Object mDataLock = new Object();
static final int START_VERSION = -1;
@SuppressWarnings("WeakerAccess") /* synthetic access */
static final Object NOT_SET = new Object();

private SafeIterableMap<Observer<? super T>, ObserverWrapper> mObservers =
        new SafeIterableMap<>();

// how many observers are in active state
@SuppressWarnings("WeakerAccess") /* synthetic access */
int mActiveCount = 0;
// to handle active/inactive reentry, we guard with this boolean
private boolean mChangingActiveState;
private volatile Object mData; // 1️⃣：当前的data
// when setData is called, we set the pending data and actual data swap happens on the main
// thread
@SuppressWarnings("WeakerAccess") /* synthetic access */
volatile Object mPendingData = NOT_SET; // 2️⃣：给多线程使用的，在4️⃣mPostValueRunnable中使用
private int mVersion; // 3️⃣：mVersion是数据版本

private boolean mDispatchingValue;
@SuppressWarnings("FieldCanBeLocal")
private boolean mDispatchInvalidated;
private final Runnable mPostValueRunnable = new Runnable() {// 4️⃣mPostValueRunnable，在主线程中将mPendingData设置为当前值
    @SuppressWarnings("unchecked")
    @Override
    public void run() {
        Object newValue;
        synchronized (mDataLock) {
            newValue = mPendingData;
            mPendingData = NOT_SET;
        }
        setValue((T) newValue);
    }
};

/** @hide */
@IntDef(flag = true, prefix = { "MODE_" }, value = {
        MODE_PRIVATE,
        MODE_WORLD_READABLE,
        MODE_WORLD_WRITEABLE,
        MODE_APPEND,
})
@Retention(RetentionPolicy.SOURCE)
public @interface FileMode {}

/** @hide */
@IntDef(flag = true, prefix = { "MODE_" }, value = {
        MODE_PRIVATE,
        MODE_WORLD_READABLE,
        MODE_WORLD_WRITEABLE,
        MODE_MULTI_PROCESS,
})
@Retention(RetentionPolicy.SOURCE)
public @interface PreferencesMode {}

/** @hide */
@IntDef(flag = true, prefix = { "MODE_" }, value = {
        MODE_PRIVATE,
        MODE_WORLD_READABLE,
        MODE_WORLD_WRITEABLE,
        MODE_ENABLE_WRITE_AHEAD_LOGGING,
        MODE_NO_LOCALIZED_COLLATORS,
})
@Retention(RetentionPolicy.SOURCE)
public @interface DatabaseMode {}

/**
 * Finds the first descendant view with the given ID, the view itself if
 * the ID matches {@link #getId()}, or {@code null} if the ID is invalid
 * (< 0) or there is no matching view in the hierarchy.
 * <p>
 * <strong>Note:</strong> In most cases -- depending on compiler support --
 * the resulting view is automatically cast to the target class type. If
 * the target class type is unconstrained, an explicit cast may be
 * necessary.
 *
 * @param id the ID to search for
 * @return a view with given ID if found, or {@code null} otherwise
 * @see View#requireViewById(int)
 */
@Nullable
public final <T extends View> T findViewById(@IdRes int id) {
    if (id == NO_ID) {
        return null;
    }
    return findViewTraversal(id);
}