<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 進度條 -->  <!-- progress 當前進度 -->  <!-- indeterminate 不明確的  默認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>

<?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">開始</string>  <string name="stop">暫停</string>  <string name="contin">繼續</string></resources>

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;/** * 只有創建一個 View 的線程才可以改變這個 View 的UI!!! 主線程也叫 UI 線程 */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();    // 設置按鈕內容 ----并沒有用...    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 {          // 打開 URL 必須在子線程          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;              // 注意強轉方式，防止一直為0              percent = (int) (100.0 * sum / contentLength);              // 在主線程上運行的子線程              runOnUiThread(new Runnable() {                @Override                public void run() {                  progressBar1.setProgress(percent);                  textView1.setText(percent + "%");                  if (percent == progressBar1.getMax()) {                    Toast.makeText(MainActivity.this,                        "下載完成!", Toast.LENGTH_SHORT)                        .show();                  }                }              });            }            is.close();            conn.disconnect();          }        } catch (IOException e) {          e.printStackTrace();        }      }    }).start();  }}