《第一行代码Android》学习总结第十章 Service实践——下载功能示例
1、在app/build.gradle文件，dependencies闭包中添加依赖。
compile 'com.squareup.okhttp3:okhttp:3.4.1'2、定义DownloadListener回调接口，用于对下载过程中的状态进行监听和回调。
public interface DownloadListener {
void onProgress(int progress); //通知当前下载进度
void onSuccess(); //通知下载成功事件
void onFailed(); //通知下载失败事件
void onPaused(); //通知下载暂停事件
void onCanceled(); //通知下载取消事件
}
3、新建DownloadTask继承自AsyncTask。
public class DownloadTask extends AsyncTask {
//下载状态通过该参数回调
public static final int TYPE_SUCCESS = 0;
public static final int TYPE_FAILED = 1;
public static final int TYPE_PAUSED = 2;
public static final int TYPE_CANCELED = 3;
private DownloadListener listener;
private boolean isCanceled = false;
private boolean isPaused = false;
private int lastProgress;
public DownloadTask(DownloadListener listener) {
//下载状态会根据该参数回调
this.listener = listener;
}
//后台执行下载逻辑
@Override
protected Integer doInBackground(String... params) {
InputStream is = null;
RandomAccessFile saveFile = null;
File file = null;
try {
long downloadedLength = 0; //记录已下载的文件长度
String downloadUrl = params[0];
String fileName = downloadUrl.substring(downloadUrl.lastIndexOf("/"));
String directory = Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS).getPath();
file = new File(directory + fileName);
if(file.exists()){
//读取已下载的字节数，用于断点续传
downloadedLength = file.length();
}
long contentLength = getContentLength(downloadUrl); //文件总字节
if(contentLength == 0){
return TYPE_FAILED;
}else if(contentLength == downloadedLength){
return TYPE_SUCCESS;
}
OkHttpClient client = new OkHttpClient();
Request request = new Request.Builder()
//断点续传
.addHeader("RANGE", "bytes=" + downloadedLength + "-")
.url(downloadUrl)
.build();
Response response = client.newCall(request).execute();
if(request != null){
is = response.body().byteStream();
saveFile = new RandomAccessFile(file, "rw");
saveFile.seek(downloadedLength);
byte[] b = new byte[1024];
int total = 0;
int len;
//读取数据写入本地
while((len = is.read(b)) != -1){
if(isCanceled){
return TYPE_CANCELED;
}else if(isPaused){
return TYPE_PAUSED;
}else {
total += len;
saveFile.write(b, 0, len);
int progress = (int) ((total + downloadedLength) * 100 / contentLength);
publishProgress(progress);
}
}
response.body().close();
return TYPE_SUCCESS;
}
}catch (Exception e){
e.printStackTrace();
}finally {
try {
if(is != null){
is.close();
}
if(saveFile != null){
saveFile.close();
}
if(isCanceled && file != null){
file.delete();
}
}catch (Exception e){
e.printStackTrace();
}
}
return TYPE_FAILED;
}
//界面更新下载进度
@Override
protected void onProgressUpdate(Integer... values) {
int progress = values[0];
if(progress > lastProgress){
listener.onProgress(progress);
lastProgress = progress;
}
}
//通知最终下载结果
@Override
protected void onPostExecute(Integer status) {
switch (status){
case TYPE_SUCCESS:
listener.onSuccess();
break;
case TYPE_FAILED:
listener.onFailed();
break;
case TYPE_PAUSED:
listener.onPaused();
break;
case TYPE_CANCELED:
listener.onCanceled();
break;
default:
break;
}
}
//暂停
public void pauseDownload(){
isPaused = true;
}
//取消
public void cancelDownload(){
isCanceled = true;
}
private long getContentLength(String downloadUrl) throws IOException {
OkHttpClient client = new OkHttpClient();
Request request = new Request.Builder()
.url(downloadUrl)
.build();
Response response = client.newCall(request).execute();
if(response != null && response.isSuccessful()){
long contentLength = response.body().contentLength();
response.body().close();
return contentLength;
}
return 0;
}
}
4、新建DownloadService继承自Service。
public class DownloadService extends Service {
private DownloadTask downloadTask;
private String downloadUrl;
//匿名类
private DownloadListener listener = new DownloadListener() {
@Override
public void onProgress(int progress) {
//触发通知
getNotificationManager().notify(1, getNotification("Downloading...", progress));
}
@Override
public void onSuccess() {
downloadTask = null;
//下载成功时关闭前台服务，并创建下载成功的通知。
stopForeground(true);
getNotificationManager().notify(1, getNotification("Download Success", -1));
Toast.makeText(DownloadService.this, "Download Success", Toast.LENGTH_SHORT).show();
}
@Override
public void onFailed() {
downloadTask = null;
//下载失败时关闭前台服务，并创建下载失败的通知。
stopForeground(true);
getNotificationManager().notify(1, getNotification("Download Failed", -1));
Toast.makeText(DownloadService.this, "Download Failed", Toast.LENGTH_SHORT).show();
}
@Override
public void onPaused() {
downloadTask = null;
Toast.makeText(DownloadService.this, "Paused", Toast.LENGTH_SHORT).show();
}
@Override
public void onCanceled() {
downloadTask = null;
stopForeground(true);
Toast.makeText(DownloadService.this, "Canceled", Toast.LENGTH_SHORT).show();
}
};
private DownloadBinder mBinder = new DownloadBinder();
@Override
public IBinder onBind(Intent intent) {
return mBinder;
}
//用于活动与服务通信
class DownloadBinder extends Binder{
public void startDownload(String url){
if(downloadTask == null){
downloadUrl = url;
downloadTask =new DownloadTask(listener);
//执行DownloadTask后台下载
downloadTask.execute(downloadUrl);
//开始前台服务
startForeground(1, getNotification("Downloading...",0));
Toast.makeText(DownloadService.this, "Downloading...", Toast.LENGTH_SHORT).show();
}
}
public void pauseDownload(){
if(downloadTask != null){
downloadTask.pauseDownload();
}
}
public void cancelDownload(){
if(downloadTask != null){
downloadTask.cancelDownload();
}
if(downloadUrl != null){
//取消下载时需删除文件并将通知关闭
String fileName = downloadUrl.substring(downloadUrl.lastIndexOf("/"));
String directory = Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS).getPath();
File file =new File(directory + fileName);
if(file.exists()){
file.delete();
}
getNotificationManager().cancel(1);
stopForeground(true);
Toast.makeText(DownloadService.this, "Canceled", Toast.LENGTH_SHORT).show();
}
}
}
private NotificationManager getNotificationManager() {
return (NotificationManager) getSystemService(NOTIFICATION_SERVICE);
}
private Notification getNotification(String title, int progress) {
Intent intent = new Intent(this, MainActivity.class);
PendingIntent pi = PendingIntent.getActivity(this, 0, intent, 0);
NotificationCompat.Builder builder = new NotificationCompat.Builder(this);
builder.setSmallIcon(R.mipmap.ic_launcher);
builder.setLargeIcon(BitmapFactory.decodeResource(getResources(), R.mipmap.ic_launcher));
builder.setContentIntent(pi);
builder.setContentTitle(title);
if(progress>0){
builder.setContentText(progress + "%");
// setProgress()方法：在通知上设置进度条，参数一传入通知最大进度，参数二传入通知当前进度，参数三表示是否使用模糊进度条
builder.setProgress(100, progress, false);
}
return builder.build();
}
}
5、修改activity_main中代码，添加三个按钮用于开始下载，暂停下载和取消下载。
6、修改MainActivity中代码。
public class MainActivity extends AppCompatActivity implements View.OnClickListener{
private DownloadService.DownloadBinder downloadBinder;
//匿名类
private ServiceConnection connection = new ServiceConnection() {
@Override
public void onServiceConnected(ComponentName componentName, IBinder service) {
//获取DownloadService实例，用于活动与服务通信
downloadBinder = (DownloadService.DownloadBinder) service;
}
@Override
public void onServiceDisconnected(ComponentName componentName) {
}
};
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Button startDownload = (Button) findViewById(R.id.start_download);
Button pauseDownload = (Button) findViewById(R.id.pause_download);
Button cancelDownload = (Button) findViewById(R.id.cancel_download);
startDownload.setOnClickListener(this);
pauseDownload.setOnClickListener(this);
cancelDownload.setOnClickListener(this);
Intent intent = new Intent(this, DownloadService.class);
startService(intent); //启动服务
//绑定服务，让活动与服务通信
bindService(intent, connection, BIND_AUTO_CREATE);
if(ContextCompat.checkSelfPermission(MainActivity.this, Manifest.permission.WRITE_EXTERNAL_STORAGE) != PackageManager.PERMISSION_GRANTED){
ActivityCompat.requestPermissions(MainActivity.this, new String[] { Manifest.permission.WRITE_EXTERNAL_STORAGE }, 1);
}
}
@Override
public void onClick(View view) {
if(downloadBinder == null){
return;
}
switch (view.getId()){
case R.id.start_download:
String url = "https://raw.githubusercontent.com/guolindev/eclipse/master/eclipse-inst-win64.exe";
downloadBinder.startDownload(url);
break;
case R.id.pause_download:
downloadBinder.pauseDownload();
break;
case R.id.cancel_download:
downloadBinder.cancelDownload();
break;
default:
break;
}
}
@Override
public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {
switch (requestCode){
case 1:
if(grantResults.length > 0 && grantResults[0] != PackageManager.PERMISSION_GRANTED){
Toast.makeText(this, "You deny the permission", Toast.LENGTH_SHORT).show();
finish();
}
break;
default:
}
}
@Override
protected void onDestroy() {
super.onDestroy();
unbindService(connection); //解绑服务
}
}
7、在AndroidManifest中进行权限声明。