WindowManager 源码分 TYPE_TOAST 悬浮窗权限检探究

WindowManager类是一个接口类，继承制ViewManager，Viewmanager是一个简单的接口类，很简单的理解可以知道是对View进行管理的类，里面只有三个方法，下面是源码：

 

源码分析：WindowManager，TYPE_TOAST悬浮窗权限检测问题

WindowManager类是一个接口类，继承制ViewManager，Viewmanager是一个简单的接口类，很简单的理解可以知道是对View进行管理的类，里面只有三个方法，下面是源码：
package android.view;

/** Interface to let you add and remove child views to an Activity. To get an instance
  * of this class, call {@link android.content.Context#getSystemService(java.lang.String) Context.getSystemService()}.
  */
public interface ViewManager
{
    /**
     * Assign the passed LayoutParams to the passed View and add the view to the window.
     * <p>Throws {@link android.view.WindowManager.BadTokenException} for certain programming
     * errors, such as adding a second view to a window without removing the first view.
     * <p>Throws {@link android.view.WindowManager.InvalidDisplayException} if the window is on a
     * secondary {@link Display} and the specified display can't be found
     * (see {@link android.app.Presentation}).
     * @param view The view to be added to this window.
     * @param params The LayoutParams to assign to view.
     */
    public void addView(View view, ViewGroup.LayoutParams params);
    public void updateViewLayout(View view, ViewGroup.LayoutParams params);
    public void removeView(View view);
}

下面是WindowMananger的源码头部：

/**
 * The interface that apps use to talk to the window manager.
 * <p>
 * Use <code>Context.getSystemService(Context.WINDOW_SERVICE)</code> to get one of these.
 * </p><p>
 * Each window manager instance is bound to a particular {@link Display}.
 * To obtain a {@link WindowManager} for a different display, use
 * {@link Context#createDisplayContext} to obtain a {@link Context} for that
 * display, then use <code>Context.getSystemService(Context.WINDOW_SERVICE)</code>
 * to get the WindowManager.
 * </p><p>
 * The simplest way to show a window on another display is to create a
 * {@link Presentation}.  The presentation will automatically obtain a
 * {@link WindowManager} and {@link Context} for that display.
 * </p>
 *
 * @see android.content.Context#getSystemService
 * @see android.content.Context#WINDOW_SERVICE
 */
public interface WindowManager extends ViewManager 
我们从@see 可以看到我们获取WindowManager的方法是Context的getSystemService方法，只需要传入参数WINDOW_SERVICE就行，比如下面

WindowManager mWm = (WindowManager) getApplicationContext().getSystemService(Context.WINDOW_SERVICE);

WindowManager的实现类是WindowManagerImpl，见下面源码，
这个WindowManagerIpml有两个，分别位于不同的包下面，
package android.view;
package com.android.layoutlib.bridge.android.view;

第一个：WindowManagerImpl
package android.view;

package android.view;

import android.annotation.NonNull;
import android.os.IBinder;

/**
 * Provides low-level communication with the system window manager for
 * operations that are bound to a particular context, display or parent window.
 * Instances of this object are sensitive to the compatibility info associated
 * with the running application.
 *
 * This object implements the {@link ViewManager} interface,
 * allowing you to add any View subclass as a top-level window on the screen.
 * Additional window manager specific layout parameters are defined for
 * control over how windows are displayed.  It also implements the {@link WindowManager}
 * interface, allowing you to control the displays attached to the device.
 * 
 * <p>Applications will not normally use WindowManager directly, instead relying
 * on the higher-level facilities in {@link android.app.Activity} and
 * {@link android.app.Dialog}.
 * 
 * <p>Even for low-level window manager access, it is almost never correct to use
 * this class.  For example, {@link android.app.Activity#getWindowManager}
 * provides a window manager for adding windows that are associated with that
 * activity -- the window manager will not normally allow you to add arbitrary
 * windows that are not associated with an activity.
 *
 * @see WindowManager
 * @see WindowManagerGlobal
 * @hide
 */
public final class WindowManagerImpl implements WindowManager {
    private final WindowManagerGlobal mGlobal = WindowManagerGlobal.getInstance();
    private final Display mDisplay;
    private final Window mParentWindow;

    private IBinder mDefaultToken;<