Android 实现系统级别弹窗

                        /**                            
                          * 进行系统弹窗
                          */
                        AlertDialog.Builder builder = new AlertDialog.Builder(getApplicationContext());
                        builder.setView(R.layout.dialog_app);
                        final AlertDialog alertDialog = builder.create();

                        if (Build.VERSION.SDK_INT < Build.VERSION_CODES.O) {
                            alertDialog.getWindow().setType(WindowManager.LayoutParams.TYPE_SYSTEM_ALERT);

                        } else {
                            alertDialog.getWindow().setType(WindowManager.LayoutParams.TYPE_APPLICATION_OVERLAY);
                        }

                        View view = alertDialog.getLayoutInflater().inflate(布局资源文件, null);
                        alertDialog.setView(view, 0, 0, 0, 0);
                        alertDialog.show();
                        view.findViewById(R.id.but_up).setOnClickListener(new View.OnClickListener() {
                            @Override
                            public void onClick(View v) {
                                startActivity(new Intent(getContext(), MainActivity.class));

                                PreferenceHelper.putString("status", "showPay");
                                alertDialog.dismiss();
                            }
                        });
                        view.findViewById(R.id.btn_cancel).setOnClickListener(new View.OnClickListener() {
                            @Override
                            public void onClick(View v) {
                                alertDialog.dismiss();
                            }
                        });

因为在Android 8.0 以后，要完成系统级弹窗之前的TYPE_SYSTEM_ALERT已经不能使用，改为了TYPE_APPLICATION_OVERLAY。