使用这个，自定义AlertDialog在你手里都不是问题

CustomDialogBuilder.With(this)//上下文
                        .load(R.layout.dialog_loading)//自定义的布局文件
                        .setDimAmount(0.5f)//设置背景透明度
                        .setCancelable(true)//是否点击区域外隐藏
                        .setHeigh(DensityUtil.dip2px(this,100))//设置高度
                        .setWidth(DensityUtil.dip2px(this,100))//设置宽度
                        .setWidth(0.5f)//设置宽度，以屏幕宽度为基准，取百分比
                        .InitView(null)//初始化View
                        .InitEvent(null)//初始化事件
                        .show();//显示

import android.app.Activity;
import android.app.Fragment;
import android.content.Context;
import android.support.annotation.LayoutRes;
import android.support.v4.app.FragmentActivity;
import android.support.v7.app.AlertDialog;

import com.xiaolei.easyfreamwork.R;
import com.xiaolei.easyfreamwork.application.ApplicationBreage;
import com.xiaolei.easyfreamwork.utils.Log;

/**
* Created by xiaolei on 2017/10/9.
*/

public class CustomDialogBuilder
{
   private boolean isBackNet = false;
   private AlertDialog.Builder builder;
   private Context context;
   private CustomDialogBuilder(Context context)
   {
       this.context = context;
       if (Activity.class.isInstance(context)
               || FragmentActivity.class.isInstance(context))
       {
           if ((Activity.class.isInstance(context) && !((Activity) context).isFinishing())
                   || (FragmentActivity.class.isInstance(context) && !((FragmentActivity) context).isFinishing()))
           {
               builder = new AlertDialog.Builder(context);
           } else
           {
               Log.e("LOG", "不是activity，或者activity已关闭");
           }
       } else
       {
           builder = new AlertDialog.Builder(ApplicationBreage.getInstance().getContext(),
                   R.style.Base_Theme_AppCompat_Light_Dialog);
           isBackNet = true;
       }
   }

   public static CustomDialogBuilder With(Activity activity)
   {
       return new CustomDialogBuilder(activity);
   }

   public static CustomDialogBuilder With(FragmentActivity activity)
   {
       return new CustomDialogBuilder(activity);
   }

   public static CustomDialogBuilder With(Fragment fragment)
   {
       return new CustomDialogBuilder(fragment.getActivity());
   }

   public static CustomDialogBuilder With(android.support.v4.app.Fragment fragment)
   {
       return new CustomDialogBuilder(fragment.getActivity());
   }

   public static CustomDialogBuilder With(Context context)
   {
       return new CustomDialogBuilder(context);
   }

   /**
    * 加载布局文件
    *
    * @param layout
    */
   public DialogInitConfig load(@LayoutRes int layout)
   {
       return new DialogInitConfig(layout,builder,isBackNet,context);
   }

   public Context getContext()
   {
       return context;
   }
}

import android.content.Context;
import android.graphics.Color;
import android.graphics.drawable.ColorDrawable;
import android.support.annotation.FloatRange;
import android.support.annotation.LayoutRes;
import android.support.v7.app.AlertDialog;
import android.util.DisplayMetrics;
import android.view.Gravity;
import android.view.View;
import android.view.Window;
import android.view.WindowManager;

/**
 * 
 * Created by xiaolei on 2017/10/9.
 */

public class DialogInitConfig
{
    private DialogInitCallBack initCallBack;
    private DialogEventCallBack eventCallBack;
    private int width = -1, heigh = -1;
    private float dimAmount = 0f;
    @LayoutRes
    private int layout = -1;
    private AlertDialog.Builder builder;
    private boolean isBackNet = false;
    private boolean cancelable = true;
    private Context context;
    
    public DialogInitConfig(@LayoutRes int layout, AlertDialog.Builder builder, boolean isBackNet, Context context)
    {
        this.layout = layout;
        this.builder = builder;
        this.isBackNet = isBackNet;
        this.context = context;
    }

    /**
     * 获取上下文
     * @return
     */
    public Context getContext()
    {
        return context;
    }

    /**
     * 初始化UI
     * @param callBack
     * @return
     */
    public DialogInitConfig InitView(DialogInitCallBack callBack)
    {
        initCallBack = callBack;
        return this;
    }

    /**
     * 初始化事件
     * @param callBack
     * @return
     */
    public DialogInitConfig InitEvent(DialogEventCallBack callBack)
    {
        eventCallBack = callBack;
        return this;
    }

    /**
     * 设置宽度，绝对的值
     * @param width
     * @return
     */
    public DialogInitConfig setWidth(int width)
    {
        this.width = width;
        return this;
    }

    /**
     * 设置宽度，屏幕的百分比的
     * @param widthPercent
     * @return
     */
    public DialogInitConfig setWidth(@FloatRange(from = 0.0,to = 1.0) double widthPercent)
    {
        WindowManager wm = (WindowManager) getContext().getSystemService(Context.WINDOW_SERVICE);
        this.width = (int) (wm.getDefaultDisplay().getWidth() * widthPercent);
        return this;
    }

    /**
     * 设置高度
     * @param heigh
     * @return
     */
    public DialogInitConfig setHeigh(int heigh)
    {
        this.heigh = heigh;
        return this;
    }

    /**
     * 设置背景透明度
     * @param dimAmount
     * @return
     */
    public DialogInitConfig setDimAmount(@FloatRange(from = 0.0,to = 1.0) float dimAmount)
    {
        this.dimAmount = dimAmount;
        return this;
    }

    /**
     * 设置是否可以点击侧边取消
     * @param cancelable
     * @return
     */
    public DialogInitConfig setCancelable(boolean cancelable)
    {
        this.cancelable = cancelable;
        return this;
    }

    /**
     * 显示出来
     * @return  返回一个dialog，方便dismiss
     */
    public AlertDialog show()
    {
        if (builder == null)
        {
            return null;
        }
        builder.setTitle("");
        builder.setMessage("");
        builder.setCancelable(cancelable);
        
        AlertDialog alertDialog = builder.create();
        if (alertDialog == null)
        {
            return null;
        }
        Window window = alertDialog.getWindow();
        if (window != null)
        {
            WindowManager.LayoutParams params = window.getAttributes();
            // 去除四角黑色背景  
            window.setBackgroundDrawable(new ColorDrawable(Color.TRANSPARENT));
            if (isBackNet)
            {
                window.setType(WindowManager.LayoutParams.TYPE_TOAST);
            }
            window.setAttributes(params);
        }
        alertDialog.show();
        try
        {
            View view = View.inflate(alertDialog.getContext(), layout, null);
            alertDialog.setContentView(view);
            if (initCallBack != null)
            {
                initCallBack.onInit(alertDialog, view);
            }
            if (eventCallBack != null)
            {
                eventCallBack.initEvent(alertDialog, view);
            }
            
            window = alertDialog.getWindow();
            if (window != null)
            {
                WindowManager.LayoutParams params = window.getAttributes();
                window.setGravity(Gravity.CENTER);
                DisplayMetrics dm = new DisplayMetrics();
                window.getWindowManager().getDefaultDisplay().getMetrics(dm);
                if (width != -1)
                {
                    params.width = width;
                }
                if (heigh != -1)
                {
                    params.height = heigh;
                }
                // 设置周围的暗色系数  
                params.dimAmount = dimAmount;
                window.setAttributes(params);
            }
        } catch (Exception e)
        {
            e.printStackTrace();
        }
        return alertDialog;
    }
    
    public interface DialogInitCallBack
    {
        public void onInit(AlertDialog alertDialog, View view);
    }

    public interface DialogEventCallBack
    {
        public void initEvent(AlertDialog alertDialog, View view);
    }
}