使用WebView显示网页（四）

package com.example.webview;

import android.annotation.SuppressLint;
import android.app.Activity;
import android.app.ProgressDialog;
import android.os.Bundle;
import android.view.KeyEvent;
import android.webkit.WebChromeClient;
import android.webkit.WebSettings;
import android.webkit.WebView;
import android.webkit.WebViewClient;

public class MainActivity extends Activity {

    private String url = "";
    private WebView webView;
    private ProgressDialog dialog;

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

    @SuppressLint("SetJavaScriptEnabled")
    private void init() {
        webView = (WebView) findViewById(R.id.id_webView);
        webView.loadUrl(url);
        // 使网页可以在webView中直接打开
        webView.setWebViewClient(new WebViewClient() {
            @Override
            public boolean shouldOverrideUrlLoading(WebView view, String url) {
                // 返回值是true的时候控制网页在webView中去打开，如果
                // 为false就调用系统 浏览器
                view.loadUrl(url);
                return true;
            }
            // WebViewClient帮助WebView去处理一些页面控制和请求通知

        });
        // 启用支持javaScript
        WebSettings settings = webView.getSettings();
        settings.setJavaScriptEnabled(true);
        // WebView加载页面优先使用缓存加载
        settings.setCacheMode(WebSettings.LOAD_CACHE_ELSE_NETWORK);
        webView.setWebChromeClient(new WebChromeClient() {
            @Override
            public void onProgressChanged(WebView view, int newProgress) {

                // newProgress 1-100之间的整数
                if (newProgress == 100) {
                    // 网页加载完毕
                    closeDialog();
                } else {
                    // 网页正在加载,打开ProgressDialog
                    openDialog(newProgress);
                }
                super.onProgressChanged(view, newProgress);
            }

            private void closeDialog() {
                if (dialog != null && dialog.isShowing()) {
                    dialog.dismiss();
                    dialog = null;
                }
            }

            private void openDialog(int newProgress) {
                if (dialog == null) {
                    dialog = new ProgressDialog(MainActivity.this);
                    dialog.setTitle("正在加载...");
                    dialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);
                    dialog.setProgress(newProgress);
                    dialog.show();
                } else {
                    dialog.setProgress(newProgress);
                }
            }
        });
    }

    // 改写物理按键返回的逻辑
    @Override
    public boolean onKeyDown(int keyCode, KeyEvent event) {

        if (keyCode == KeyEvent.KEYCODE_BACK) {
            // Toast.makeText(this, webView.getUrl(),
            // Toast.LENGTH_SHORT).show();

            if (webView.canGoBack()) {
                // 返回上一页面
                webView.goBack();
                return true;
            } else {
                System.exit(0);
            }
        }
        return super.onKeyDown(keyCode, event);
    }
}