<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context=".MainActivity">

    <ProgressBar
        android:id="@+id/pb"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
/>

    <Button
        android:onClick="myClick"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="显示隐藏进度条"/>

<!--    想有一点点加载的效果就得设置max-->
    <ProgressBar
        android:id="@+id/pb2"
        style="?android:attr/progressBarStyleHorizontal"
        android:max="100"
        android:layout_width="300dp"
        android:layout_height="wrap_content"/>

    <Button
        android:onClick="myLoder"
        android:text="模拟下载，增加一点"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"/>

    <ProgressBar
        android:id="@+id/pb3"
        style="?android:attr/progressBarStyleHorizontal"
        android:max="100"
        android:layout_width="300dp"
        android:indeterminate="true"
        android:layout_height="wrap_content"/>

</LinearLayout>

package com.example.myprogressbar2;

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;
import android.view.View;
import android.widget.ProgressBar;

public class MainActivity extends AppCompatActivity {

    private ProgressBar progressBar;
    private ProgressBar progressBar2;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        progressBar = findViewById(R.id.pb);
    }

    public void myClick(View view) {
        //进度条目前没显示则让他显示
        if (progressBar.getVisibility() == View.GONE){
            progressBar.setVisibility(View.VISIBLE);
        }else {
            progressBar.setVisibility(View.GONE);
        }
    }

    public void myLoder(View view) {
        progressBar2 = findViewById(R.id.pb2);
        //获取进度条的值（进度）
        int progress = progressBar2.getProgress();
        progress+=10;
        progressBar2.setProgress(progress);
    }
}