这篇文章给大家介绍怎么在Android中利用Handler实现一个文件下载功能，内容非常详细，感兴趣的小伙伴们可以参考借鉴，希望对大家能有所帮助。
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代码实现
在AndroidManifest.xml文件中声明申请的权限，如下所示：
新建一个名为DownloadDemo的项目，activity_main.xml代码如下：
MainActivity.class代码如下：
public class MainActivity extends AppCompatActivity implements View.OnClickListener {
public static final String APP_URL = "http://download.sj.qq.com/upload/connAssitantDownload/upload/MobileAssistant_1.apk";
public static final int DOWNLOAD_MESSAGE_CODE = 100001;
private static final int DOWNLOAD_MESSAGE_FAIL_CODE = 100002;
public static final int REQUEST_CODE = 1;
private Button button;
private ProgressBar progressBar;
private MyHandler mHandler;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
initView();
askPermission();
mHandler = new MyHandler(this);
}
public static class MyHandler extends Handler {
final WeakReference mWeakReference;
public MyHandler(MainActivity activity) {
this.mWeakReference = new WeakReference<>(activity);
}
@Override
public void handleMessage(Message msg) {
MainActivity activity = mWeakReference.get();
super.handleMessage(msg);
switch (msg.what) {
case DOWNLOAD_MESSAGE_CODE:
activity.progressBar.setProgress((Integer) msg.obj);
if (((Integer) msg.obj) == 100) {
Toast.makeText(activity, "文件下载已完成！", Toast.LENGTH_SHORT).show();
}
break;
case DOWNLOAD_MESSAGE_FAIL_CODE:
Toast.makeText(activity, "文件下载失败！", Toast.LENGTH_SHORT).show();
break;
}
}
}
/**
* 申请权限
*/
private void askPermission() {
//将所需申请的权限添加到List集合中
List permissionList = new ArrayList<>();
if (ContextCompat.checkSelfPermission(MainActivity.this,
Manifest.permission.WRITE_EXTERNAL_STORAGE) != PackageManager.PERMISSION_GRANTED) {
permissionList.add(Manifest.permission.WRITE_EXTERNAL_STORAGE);
}
//判断权限列表是否为空，若不为空，则向用户申请权限，否则则直接执行操作
if (!permissionList.isEmpty()) {
String[] permissions = permissionList.toArray(new String[permissionList.size()]);
ActivityCompat.requestPermissions(MainActivity.this, permissions, REQUEST_CODE);
} else {
//TODO
button.setOnClickListener(this);
}
}
/**
* 用户对请求权限的dialog做出响应之后,会处理请求权限的响应
*
* @param requestCode 请求码
* @param permissions 权限的集合
* @param grantResults 权限授予的结果
*/
@Override
public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {
super.onRequestPermissionsResult(requestCode, permissions, grantResults);
switch (requestCode) {
case REQUEST_CODE:
if (grantResults.length > 0) {
for (int result : grantResults) {
if (result != PackageManager.PERMISSION_GRANTED) {
Toast.makeText(this, "必须同意所有权限才能使用本程序", Toast.LENGTH_SHORT).show();
finish();
return;
}
}
//TODO
button.setOnClickListener(this);
} else {
Toast.makeText(this, "权限申请失败！", Toast.LENGTH_SHORT).show();
finish();
}
break;
default:
break;
}
}
/**
* 点击事件
*
* @param v
*/
@Override
public void onClick(View v) {
switch (v.getId()) {
case R.id.button:
new Thread(new Runnable() {
@Override
public void run() {
download(APP_URL);
}
}).start();
break;
}
}
/**
* 下载
*
* @param appUrl
*/
private void download(String appUrl) {
try {
//实例化一个url对象
URL url = new URL(appUrl);
//获取URLConnection对象
URLConnection urlConnection = url.openConnection();
//获取输入流
InputStream inputStream = urlConnection.getInputStream();
//获取文件的总长度
int contentLength = urlConnection.getContentLength();
//设置软件下载到手机存储的位置文件夹名称
String downloadFolderName = Environment.getExternalStorageDirectory()
+ File.separator + "MyApp" + File.separator;
File file = new File(downloadFolderName);
//若文件夹不存在则进行创建
if (!file.exists()) {
file.mkdir();
}
String fileName = downloadFolderName + "chaixingsi.apk";
File apkFile = new File(fileName);
if (apkFile.exists()) {
apkFile.delete();
}
int downloadContentLength = 0;
int length = 0;
byte[] bytes = new byte[1024];
OutputStream outputStream = new FileOutputStream(fileName);
while ((length = inputStream.read(bytes)) != -1) {
outputStream.write(bytes, 0, length);
downloadContentLength += length;
/**
* 发送消息通知主线程去更新UI
*/
Message message = Message.obtain();
message.obj = downloadContentLength * 100 / contentLength;
message.what = DOWNLOAD_MESSAGE_CODE;
mHandler.sendMessage(message);
}
inputStream.close();
outputStream.close();
} catch (MalformedURLException e) {
//下载失败的话也发送消息
notifyDownloadFailed();
e.printStackTrace();
} catch (IOException e) {
notifyDownloadFailed();
e.printStackTrace();
}
}
/**
* 通知下载失败
*/
private void notifyDownloadFailed() {
Message message = Message.obtain();
message.what = DOWNLOAD_MESSAGE_FAIL_CODE;
mHandler.sendMessage(message);
}
/**
* 初始化视图
*/
private void initView() {
button = findViewById(R.id.button);
progressBar = findViewById(R.id.progressBar);
}
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