随着新外观的 Android ADT（Android 开发者工具）有一些新的项目向导，它们比我习惯的旧的 hello world 模板更进一步，我试图理解它们，但发现它真的很困难。
我正在查看全屏项目向导。
enter code here当您使用此向导创建项目时，它将创建一个包含文件 SystemUIHider.java 的 util 库。
这是问题。
我懂了：
protected OnVisibilityChangeListener mOnVisibilityChangeListener = sDummyListener;
它调用了类文件底部的接口：
public interface OnVisibilityChangeListener {
public void onVisibilityChange(boolean visible);
}
我的问题是：
1）我认为必须扩展接口，那么这段代码有什么实际用途？
2）如果 OnVisibilityChangeListener 是一个接口而不是严格来说是一个类，这怎么可能？
private static OnVisibilityChangeListener sDummyListener = new OnVisibilityChangeListener() {
@Override
public void onVisibilityChange(boolean visible) {
}
};
谢谢 ！
package com.example.test2.util;
import android.app.Activity;
import android.os.Build;
import android.view.View;
public abstract class SystemUiHider {
/**
* When this flag is set, the
* {@link android.view.WindowManager.LayoutParams#FLAG_LAYOUT_IN_SCREEN}
* flag will be set on older devices, making the status bar "float" on top
* of the activity layout. This is most useful when there are no controls at
* the top of the activity layout.
* <p>
* This flag isn't used on newer devices because the <a
* href="http://developer.android.com/design/patterns/actionbar.html">action
* bar</a>, the most important structural element of an Android app, should
* be visible and not obscured by the system UI.
*/
public static final int FLAG_LAYOUT_IN_SCREEN_OLDER_DEVICES = 0x1;
/**
* When this flag is set, {@link #show()} and {@link #hide()} will toggle
* the visibility of the status bar. If there is a navigation bar, show and
* hide will toggle low profile mode.
*/
public static final int FLAG_FULLSCREEN = 0x2;
/**
* When this flag is set, {@link #show()} and {@link #hide()} will toggle
* the visibility of the navigation bar, if it's present on the device and
* the device allows hiding it. In cases where the navigation bar is present
* but cannot be hidden, show and hide will toggle low profile mode.
*/
public static final int FLAG_HIDE_NAVIGATION = FLAG_FULLSCREEN | 0x4;
/**
* The activity associated with this UI hider object.
*/
protected Activity mActivity;
/**
* The view on which {@link View#setSystemUiVisibility(int)} will be called.
*/
protected View mAnchorView;
/**
* The current UI hider flags.
*
* @see #FLAG_FULLSCREEN
* @see #FLAG_HIDE_NAVIGATION
* @see #FLAG_LAYOUT_IN_SCREEN_OLDER_DEVICES
*/
protected int mFlags;
/**
* The current visibility callback.
*/
protected OnVisibilityChangeListener mOnVisibilityChangeListener = sDummyListener;
/**
* Creates and returns an instance of {@link SystemUiHider} that is
* appropriate for this device. The object will be either a
* {@link SystemUiHiderBase} or {@link SystemUiHiderHoneycomb} depending on
* the device.
*
* @param activity The activity whose window's system UI should be
* controlled by this class.
* @param anchorView The view on which
* {@link View#setSystemUiVisibility(int)} will be called.
* @param flags Either 0 or any combination of {@link #FLAG_FULLSCREEN},
* {@link #FLAG_HIDE_NAVIGATION}, and
* {@link #FLAG_LAYOUT_IN_SCREEN_OLDER_DEVICES}.
*/
public static SystemUiHider getInstance(Activity activity, View anchorView, int flags) {
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB) {
return new SystemUiHiderHoneycomb(activity, anchorView, flags);
} else {
return new SystemUiHiderBase(activity, anchorView, flags);
}
}
protected SystemUiHider(Activity activity, View anchorView, int flags) {
mActivity = activity;
mAnchorView = anchorView;
mFlags = flags;
}
/**
* Sets up the system UI hider. Should be called from
* {@link Activity#onCreate}.
*/
public abstract void setup();
/**
* Returns whether or not the system UI is visible.
*/
public abstract boolean isVisible();
/**
* Hide the system UI.
*/
public abstract void hide();
/**
* Show the system UI.
*/
public abstract void show();
/**
* Toggle the visibility of the system UI.
*/
public void toggle() {
if (isVisible()) {
hide();
} else {
show();
}
}
/**
* Registers a callback, to be triggered when the system UI visibility
* changes.
*/
public void setOnVisibilityChangeListener(OnVisibilityChangeListener listener) {
if (listener == null) {
listener = sDummyListener;
}
mOnVisibilityChangeListener = listener;
}
/**
* A dummy no-op callback for use when there is no other listener set.
*/
private static OnVisibilityChangeListener sDummyListener = new OnVisibilityChangeListener() {
@Override
public void onVisibilityChange(boolean visible) {
}
};
/**
* A callback interface used to listen for system UI visibility changes.
*/
public interface OnVisibilityChangeListener {
/**
* Called when the system UI visibility has changed.
*
* @param visible True if the system UI is visible.
*/
public void onVisibilityChange(boolean visible);
}
}