webview自定义加载进度条

我们平时在进行安卓开发使用到webview加载网页时，我们不能准确了解网页的加载进度，因此为了提高用户体验，我们在webview中加入进度条显示加载进度。如下是显示效果

布局：

<?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:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="com.example.abc.myapplication.MainActivity">
    <ProgressBar
        android:id="@+id/progressBar"
        style="@style/crowd_item_progressBar"
        android:layout_width="match_parent"
        android:layout_height="3dp"
        android:background="@drawable/crowd_progressbar_background" />

   <WebView
    android:id="@+id/webview"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"></WebView>

</LinearLayout>

进度条背景色：

<layer-list xmlns:android="http://schemas.android.com/apk/res/android" >

    <item android:id="@android:id/background">
        <shape>
            <corners android:radius="2dp" />
            <gradient
                android:angle="270"
                android:centerColor="#E3E3E3"
                android:endColor="#E6E6E6"
                android:startColor="#C8C8C8" />
        </shape>
    </item>
    <item android:id="@android:id/progress">
        <clip>
            <shape>
                <corners android:radius="2dp" />
                <gradient
                    android:centerColor="#2f4eea"
                    android:endColor="#2b15ce"
                    android:startColor="#464cec" />

            </shape>
        </clip>
    </item>

</layer-list>

MainActivity代码：

package com.example.abc.myapplication;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.KeyEvent;
import android.webkit.WebChromeClient;
import android.webkit.WebResourceRequest;
import android.webkit.WebSettings;
import android.webkit.WebView;
import android.webkit.WebViewClient;
import android.widget.ProgressBar;

import static android.view.View.GONE;
import static android.view.View.VISIBLE;

public class MainActivity extends AppCompatActivity {
    private WebView webView;
    private ProgressBar progressBar;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        init();
        webView.loadUrl("http://www.baidu.com");
    }

    private void init() {
        webView=findViewById(R.id.webview);
        progressBar=findViewById(R.id.progressBar);
        webView.setWebViewClient(new WebViewClient(){
            @Override
            public boolean shouldOverrideUrlLoading(WebView view, WebResourceRequest request) {
                return super.shouldOverrideUrlLoading(view, request);
            }
        });
        WebSettings seting=webView.getSettings();
        seting.setJavaScriptEnabled(true);
        webView.setWebChromeClient(new WebChromeClient(){
            @Override
            public void onProgressChanged(WebView view, int newProgress) {
                if (newProgress == 100) {

                    progressBar.setVisibility(GONE);
                } else {

                    if (progressBar.getVisibility() == GONE)
                        progressBar.setVisibility(VISIBLE);
                    progressBar.setProgress(newProgress);

                }
                super.onProgressChanged(view, newProgress);
            }
        });
    }
    
    @Override
    public boolean onKeyDown(int keyCode, KeyEvent event) {
        if(keyCode==KeyEvent.KEYCODE_BACK) {
            if(webView.canGoBack()) {
                webView.goBack();
                return true;
            }
            else {
                System.exit(0);
            }
            
        }
        return super.onKeyDown(keyCode, event);
    }
}