Android利用AsyncTask异步类实现网页内容放大缩小

package com.supermario.filemanager;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import org.apache.http.protocol.HTTP;
import android.app.Activity;
import android.app.AlertDialog;
import android.content.DialogInterface;
import android.content.DialogInterface.OnClickListener;
import android.os.AsyncTask;
import android.os.Bundle;
import android.view.View;
import android.webkit.WebSettings;
import android.webkit.WebView;
import android.widget.RelativeLayout;
import android.widget.ZoomControls;
public class WebActivity extends Activity {
 //网页浏览器
 private WebView webView;
 //进度条布局和网页内容主体布局
 private RelativeLayout loadingLayout,webLayout;
 //放大缩小控制器
 private ZoomControls zoomControls; 
 @Override
 protected void onCreate(Bundle savedInstanceState) {
 super.onCreate(savedInstanceState);
 setContentView(R.layout.web);
 //初始化页面组件
 webView = (WebView)findViewById(R.id.webkit);
 loadingLayout = (RelativeLayout)findViewById(R.id.loadingLayout);
 webLayout = (RelativeLayout)findViewById(R.id.weblayout);
 zoomControls = (ZoomControls)findViewById(R.id.zoomControls); 
 WebSettings webSettings = webView.getSettings();
 //设置可以使用js脚本
 webSettings.setJavaScriptEnabled(true);
 //执行异步进程
 new MyAsyncTask().execute(""); 
 }
 private void reading(){
 String filePath = getIntent().getStringExtra("filePath");
 if (filePath != null) {
  //读取文件
  webView.loadData(readWebDataToStringFromPath(filePath, new FileReadOverBack() {
  @Override
  public void fileReadOver() {
  }
  }), "text/html", HTTP.UTF_8);
 } else {
  new AlertDialog.Builder(WebActivity.this).setTitle("出错了").setMessage("获取文件路径出错!").setPositiveButton("返回", new OnClickListener() {
  @Override
  public void onClick(DialogInterface dialog, int which) {
   WebActivity.this.finish();
  }
  });
 }
 }
 //将网页数据读取到一个字符串变量中
 private String readWebDataToStringFromPath(String path,final FileReadOverBack fileReadOverBack){
 File file = new File(path);
 StringBuffer stringBuffer = new StringBuffer();
 try {
  //读取文件内容
  FileInputStream inputStream = new FileInputStream(file);
  byte[] bytes = new byte[1024];
  int readCount = 0;
  while ((readCount = inputStream.read(bytes)) > 0) {
  stringBuffer.append(new String(bytes, 0, readCount));
  }
  fileReadOverBack.fileReadOver();
 } catch (FileNotFoundException e) {
  return "文件不存在!";
 } catch (IOException e) {
  return "文件读取错误!";
 }
 return stringBuffer.toString();
 } 
 interface FileReadOverBack{
 void fileReadOver();
 }
 //异步处理类
 class MyAsyncTask extends AsyncTask<String, String, String>{
 //首先执行的函数
 @Override
 protected void onPreExecute() {
  super.onPreExecute();
  loadingLayout.setVisibility(View.VISIBLE);
  webLayout.setVisibility(View.GONE);
 }
 //后台执行
 @Override
 protected String doInBackground(String... params) {
  reading();
  return null;
 } 
 @Override
 protected void onPostExecute(String result) {
  super.onPostExecute(result);
  //设置载入进度条隐藏
  loadingLayout.setVisibility(View.GONE);
  //设置浏览器内容可见
  webLayout.setVisibility(View.VISIBLE);  
  // 放大按钮
  zoomControls.setOnZoomInClickListener(new View.OnClickListener() {
  //将网页内容放大
  @Override
  public void onClick(View v) {
   webView.zoomIn();
  }
  });
  // 缩小按钮
  zoomControls.setOnZoomOutClickListener(new View.OnClickListener() { 
  //将网页内容缩小
  @Override
  public void onClick(View v) {
   webView.zoomOut();
  }
  });
 } 
 }
}