【android】自定义的dialog不弹出的原因——content上下文

附上自定义的dialog的代码：

package com.example.zegochatroom.roomchatActivity.popdialog;

import android.app.Dialog;
import android.content.Context;
import android.os.Bundle;
import android.view.Gravity;
import android.view.View;
import android.view.Window;
import android.view.WindowManager;

import com.example.zegochatroom.R;

public class GiftPopDialog extends Dialog {
    private boolean isCancelable;//控制点击dialog外部是否dismiss
    private boolean isBackCancelable;//控制返回键是否dismiss
    private int viewID;
    private Context context;


    public GiftPopDialog(Context context, int viewID, boolean isCancelable,boolean isBackCancelable) {
        super(context, R.style.MyDialog);
        this.context = context;
        this.viewID = viewID;
        this.isCancelable = isCancelable;
        this.isBackCancelable = isBackCancelable;
    }

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(viewID);//这行一定要写在前面
        setCancelable(isCancelable);//点击外部不可dismiss
        setCanceledOnTouchOutside(isBackCancelable);
        Window window = this.getWindow();
        window.setGravity(Gravity.BOTTOM);
        WindowManager.LayoutParams params = window.getAttributes();
        params.width = WindowManager.LayoutParams.MATCH_PARENT;
        params.height = WindowManager.LayoutParams.WRAP_CONTENT;
        window.setAttributes(params);
    }

}

但是我报出了这样的一个错误：

一开始，我调用的调用这个的代码如下：

GiftPopDialog giftPopDialog = new GiftPopDialog(MyApplication.getContext(),R.layout.pop_gift,false,true);
                giftPopDialog.show();

这个是错误的，没有一个具体的window告诉这个的代码应该怎么做，所以他就崩了！
正确的如下：

 GiftPopDialog giftPopDialog = new GiftPopDialog(RoombaseActivity.this,R.layout.pop_gift,false,true);
                giftPopDialog.show();