downLoad.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="640dp"
android:layout_height="260dp"
android:orientation="vertical"
>

<LinearLayout
    android:layout_width="match_parent"
    android:layout_height="0dp"
    android:layout_weight="1"
    android:background="#FF0A0A0A"
    android:gravity="center"
    android:orientation="vertical">

    <ProgressBar
        android:id="@+id/progressBar"
        style="@style/Widget.AppCompat.ProgressBar.Horizontal"
        android:layout_width="486dp"
        android:layout_height="6dp"
        android:progressDrawable="@drawable/progress_bar" />

    <TextView
        android:id="@+id/tv_progress"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="20dp"
        android:textColor="#DDDDDD"
        android:background="@android:color/transparent"
        tools:text="2.3MB / 15MB" />


</LinearLayout>

<TextView
    android:id="@+id/tv_close"
    android:layout_width="match_parent"
    android:layout_height="72dp"
    android:gravity="center"
    android:text="@string/close"
    android:textColor="#DDDDDD"
    android:background="#0ADDDDDD"
    android:textSize="26sp" />

</LinearLayout>

downLoad.java
package com.geely.util;

import android.app.AlertDialog;
import android.content.Context;
import android.support.annotation.NonNull;
import android.view.View;
import android.widget.ProgressBar;
import android.widget.TextView;

import com.geely.activity.DownloadFragment;
import com.geely.main.R;

public class DownLoadDialog extends AlertDialog {
TextView tv_progress;
ProgressBar progressBar;
TextView tv_close;
private int max;
private String mProgressNumberFormat;

public DownLoadDialog(Context context) {
    super(context);
}

private void initView() {
    getWindow().setDimAmount(0.6f);
    tv_progress = findViewById(R.id.tv_progress);
    progressBar = findViewById(R.id.progressBar);
    tv_close = findViewById(R.id.tv_close);
    tv_close.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            DownLoadDialog.this.dismiss();
            DownloadFragment.flag = false;
            if(DownloadFragment.buttonDown!=null){
                DownloadFragment.buttonDown.setEnabled(true);
            }
        }
    });
}

public int getMax() {
    return max;
}

public void setMax(int max) {
    this.max = max;
    progressBar.setMax(max);
}

public void setProgress(int progress) {
    progressBar.setProgress(progress);
    tv_progress.setText(String.format(mProgressNumberFormat,progress,max));
}

@Override
public void setContentView(@NonNull View view) {
    super.setContentView(view);
    initView();
}

@Override
public void setContentView(int layoutResID) {
    super.setContentView(layoutResID);
    initView();
}

public void setProgressNumberFormat(String s) {
    mProgressNumberFormat = s;
}

}

3.使用
private DownLoadDialog downLoadDialog;
downLoadDialog.setProgressNumberFormat("%1d M/%2d M");
downLoadDialog = new DownLoadDialog(getActivity());
downLoadDialog.setCancelable(false);//设置为不可关闭
downLoadDialog.show();
downLoadDialog.setContentView(R.layout.layout_dialog_download);
downLoadDialog.setMax(size);