Android之ProgressBar初步应用

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这里利用 ProgressBar 即时显示下载进度。

途中碰到的问题：

1、主线程中不能打开 URL，和只能在主线程中使用 Toast 等

2、子线程不能修改 UI

3、允许网络协议

4、暂停下载和继续下载

........

fragment_main 布局文件

 <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"

     xmlns:tools="http://schemas.android.com/tools"

     android:layout_width="match_parent"

     android:layout_height="match_parent"

     tools:context="com.dragon.android.textbar.MainActivity$PlaceholderFragment" >

     <!-- prigressBar 进度条 -->

     <!-- progress 当前进度 -->

     <!-- indeterminate 不明确的   默认false -->

     <ProgressBar

         android:id="@+id/progressBar1"

         style="?android:attr/progressBarStyleHorizontal"

         android:layout_width="match_parent"

         android:layout_height="wrap_content"

         android:layout_centerInParent="true"

         android:max="100"

         android:progress="0"

         android:indeterminate="true"/>

     <Button

         android:id="@+id/button1"

         android:layout_width="wrap_content"

         android:layout_height="wrap_content"

         android:layout_alignParentTop="true"

         android:layout_centerHorizontal="true"

         android:onClick="startLoad"

         android:layout_marginTop="86dp"

         android:background="#009FEE"

         android:text="@string/start"

         android:textColor="#ffffff" />

     <TextView

         android:id="@+id/textView1"

         android:layout_width="wrap_content"

         android:layout_height="wrap_content"

         android:layout_above="@+id/progressBar1"

         android:background="@null"

         android:layout_alignParentLeft="true" />

 </RelativeLayout>

fragment_main

strings.xml

 <?xml version="1.0" encoding="utf-8"?>

 <resources>

     <string name="app_name">hwdownload</string>

     <string name="hello_world">Hello world!</string>

     <string name="action_settings">Settings</string>

     <string name="start">开始</string>

     <string name="stop">暂停</string>

     <string name="contin">继续</string>

 </resources>

strings

（问题3）在 AndroidManifest 文件中配置

 <!-- 请求网络权限 -->

     <uses-permission  android:name="android.permission.INTERNET"/>

MainActivity（问题1、2）

package com.dragon.android.textbar;

import java.io.IOException;

import java.io.InputStream;

import java.net.HttpURLConnection;

import java.net.URL;

import android.app.Activity;

import android.os.Bundle;

import android.view.View;

import android.widget.Button;

import android.widget.ProgressBar;

import android.widget.TextView;

import android.widget.Toast;

/**

 * 只有创建一个 View 的线程才可以改变这个 View 的UI!!! 主线程也叫 UI 线程

 */

public class MainActivity extends Activity {

    private ProgressBar progressBar1;

    private Button button1;

    private TextView textView1;

    @Override

    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.fragment_main);

        progressBar1 = (ProgressBar) findViewById(R.id.progressBar1);

        button1 = (Button) findViewById(R.id.button1);

        textView1 = (TextView) findViewById(R.id.textView1);

    }

    public void startLoad(View view) {

         String text = (String) button1.getText();

        // 设置按钮内容 ----并没有用...

        button1.setText(text.equals(getResources().getString(R.string.start)) ? R.string.stop

                : (text.equals(getResources().getString(R.string.stop)) ? R.string.contin

                        : R.string.stop));

        progressBar1.setIndeterminate(false);

        new Thread(new Runnable() {

            private int percent;

            @Override

            public void run() {

                try {

                    // 打开 URL 必须在子线程

                    URL url = new URL(

                            "http://b.zol-img.com.cn/sjbizhi/images/9/540x960/1472549276394.jpg");

                    HttpURLConnection conn = (HttpURLConnection) url.openConnection();

                    // conn.setRequestMethod("GET");

                    // conn.setReadTimeout(5000);

                    // conn.setConnectTimeout(5000);

                    int contentLength = conn.getContentLength();

                    if (conn.getResponseCode() == HttpURLConnection.HTTP_OK) {

                        InputStream is = conn.getInputStream();

                        byte[] buffer = new byte[1024];

                        int len = -1;

                        int sum = 0;

                        while ((len = is.read(buffer)) != -1) {

                            sum += len;

                            // 注意强转方式，防止一直为0

                            percent = (int) (100.0 * sum / contentLength);

                            // 在主线程上运行的子线程

                            runOnUiThread(new Runnable() {

                                @Override

                                public void run() {

                                    progressBar1.setProgress(percent);

                                    textView1.setText(percent + "%");

                                    if (percent == progressBar1.getMax()) {

                                        Toast.makeText(MainActivity.this,

                                                "下载完成!", Toast.LENGTH_SHORT)

                                                .show();

                                    }

                                }

                            });

                        }

                        is.close();

                        conn.disconnect();

                    }

                } catch (IOException e) {

                    e.printStackTrace();

                }

            }

        }).start();

    }

}