Android之ProgressBar初步应用

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>

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>

（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();
    }
}

**************然而并没有解决问题4,要用断点续传,但是还不会存放assets资源.....***************