android M SYSTEM_ALERT_WINDOW权限问题

public class ForceOfflineReceiver extends BroadcastReceiver {    @Override    public void onReceive(final Context context,  Intent intent) {        AlertDialog.Builder dialogBuilder = new AlertDialog.Builder(context);        dialogBuilder.setTitle("Warning");        dialogBuilder.setMessage("You are forced to be offline.Please try to login again,");        dialogBuilder.setCancelable(true);        dialogBuilder.setPositiveButton("OK", new DialogInterface.OnClickListener() {            @Override            public void onClick(DialogInterface dialogInterface, int i) {                forceAllActivity(context);            }        });        AlertDialog alertDialog = dialogBuilder.create();        alertDialog.getWindow().setType(WindowManager.LayoutParams.TYPE_SYSTEM_ALERT);//因为dialog需要依附于activity显示，但是我们现在是在receiver中所以不能正常显示，我们可以通过TYPE_SYSTEM_ALERT将其声明成系统提示框然后就可以正常显示了，但是需要在manifest里面进行权限声明        alertDialog.show();    }    private void forceAllActivity(final Context context){        ActivityCollector.finishAll();        Intent intent = new Intent(context, LoginActivity.class);        intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);//在非activity中启动一个activity需要添加一个flag让其运行在一个新的堆栈中        context.startActivity(intent);    }}

<uses-permission android:name="android.permission.SYSTEM_ALERT_WINDOW"/>

在android M 以前，这样做是可以正常显示的，但是在android M 后运行就会报错，说我们没有权限，官方解释如下：

SYSTEM_ALERT_WINDOWAdded in API level 1String SYSTEM_ALERT_WINDOWAllows an app to create windows using the type TYPE_SYSTEM_ALERT, shown on top of all other apps. Very few apps should use this permission; these windows are intended for system-level interaction with the user.Note: If the app targets API level 23 or higher, the app user must explicitly grant this permission to the app through a permission management screen. The app requests the user's approval by sending an intent with action ACTION_MANAGE_OVERLAY_PERMISSION. The app can check whether it has this authorization by calling Settings.canDrawOverlays().Protection level: signatureConstant Value: "android.permission.SYSTEM_ALERT_WINDOW"

ACTION_MANAGE_OVERLAY_PERMISSIONAdded in API level 23String ACTION_MANAGE_OVERLAY_PERMISSIONActivity Action: Show screen for controlling which apps can draw on top of other apps.In some cases, a matching Activity may not exist, so ensure you safeguard against this.Input: Optionally, the Intent's data URI can specify the application package name to directly invoke the management GUI specific to the package name. For example "package:com.my.app".Output: Nothing.Constant Value: "android.settings.action.MANAGE_OVERLAY_PERMISSION"

即我们需要用户的再次确认才可以使用这个权限，再次确认的方式有两种

一、用户手动确认：Settings – Apps – setting – Draw over other apps – 选择需要权限的app – enable

二、代码中动态跳转到相应界面，让用户开启

public static int OVERLAY_PERMISSION_REQUEST_CODE = 8888;    public void requestDrawOverLays() {        if (!Settings.canDrawOverlays(LoginActivity.this)) {        //没有权限，给出提示，并跳转界面然用户enable            Toast.makeText(this, "can not DrawOverlays", Toast.LENGTH_SHORT).show();            Intent intent = new Intent(Settings.ACTION_MANAGE_OVERLAY_PERMISSION, Uri.parse("package:" + LoginActivity.this.getPackageName()));            startActivityForResult(intent, OVERLAY_PERMISSION_REQUEST_CODE);        } else {        //有权限，正常逻辑走起            Toast.makeText(this, "Permission Allowed", Toast.LENGTH_SHORT).show();        }    }    @Override    protected void onActivityResult(int requestCode, int resultCode, Intent data) {        if (requestCode == OVERLAY_PERMISSION_REQUEST_CODE) {            if (!Settings.canDrawOverlays(this)) {                // 还是没权限，说明用户不想给你这个权限，可以弹框说明                Toast.makeText(this, "Permission Denieddd by user.Please Check it in Settings", Toast.LENGTH_SHORT).show();            } else {            //用户已经给了权限，正常逻辑走起                Toast.makeText(this, "Permission Allowed", Toast.LENGTH_SHORT).show();           }        }    }

参考链接如下：

https://developer.android.com/reference/android/Manifest.permission.html
https://developer.android.com/reference/android/provider/Settings.html#ACTION_MANAGE_OVERLAY_PERMISSION
http://www.jianshu.com/p/2746a627c6d2