使用 DownloadManager 显示活动内部的下载进度

You are dividing two integers:

final double dl_progress = (bytes_downloaded / bytes_total) * 100;

As bytes_downloaded is less than bytes_total, (bytes_downloaded / bytes_total) will be 0, and your progress will therefore always be 0.

Change your calculation to

final int dl_progress = (int) ((bytes_downloaded * 100l) / bytes_total);

to obtain the progress in whole (albeit floored) percentiles.

Paul's answer is correct but with larger downloads you will hit max int pretty quick and start getting a negative progress. I used this to solve the issue:

final int dl_progress = (int) ((bytes_downloaded * 100l) / bytes_total);

As paul said, you are dividing two integers, with result always <1.

Always cast your number before divide, which calculate and return in float-point.

Don't forget to handle DivByZero.

final int dl_progress = (int) ((double)bytes_downloaded / (double)bytes_total * 100f);

In case if someone needs implementation of download progress retriever from @Victor Laerte's question in Kotlin with RxJava here you go:

DownloadStateRetriever.kt

class DownloadStateRetriever(private val downloadManager: DownloadManager) {


fun retrieve(id: Long) {
var downloading = AtomicBoolean(true)


val disposable = Observable.fromCallable {
val query = DownloadManager.Query().setFilterById(id)
val cursor = downloadManager.query(query)


cursor.moveToFirst()


val bytesDownloaded = cursor.intValue(DownloadManager.COLUMN_BYTES_DOWNLOADED_SO_FAR)
val bytesTotal = cursor.intValue(DownloadManager.COLUMN_TOTAL_SIZE_BYTES)


if (isSuccessful(cursor)) downloading.set(false)
cursor.close()


if (bytesTotal == 0) 0.toInt() else ((bytesDownloaded * 100F) / bytesTotal).toInt()
}
.subscribeOn(Schedulers.newThread())
.delay(1, TimeUnit.SECONDS)
.repeatUntil { !downloading.get() }
.subscribe {
Timber.i("Subscribed to $id. progress: $it")
}
}


private fun isSuccessful(cursor: Cursor) = status(cursor) == DownloadManager.STATUS_SUCCESSFUL


private fun status(cursor: Cursor) = cursor.intValue(DownloadManager.COLUMN_STATUS)
}

I have added extensions to cursor for more code clarity:

CursorExtensions.kt

import android.database.Cursor


fun Cursor.column(which: String) = this.getColumnIndex(which)
fun Cursor.intValue(which: String): Int = this.getInt(column(which))
fun Cursor.floatValue(which: String): Float = this.getFloat(column(which))
fun Cursor.stringValue(which: String): String = this.getString(column(which))
fun Cursor.doubleValue(which: String): Double = this.getDouble(column(which))

And in case if someone need to implementation download progress with kotlin and flows - i hope this help someone. This is @rahimli version with adding flows instead of RxJava

Retriever

private fun retrieve(id: Long) = flow {
val downloading = AtomicBoolean(true)


while (downloading.get()) {
val query = DownloadManager.Query().setFilterById(id)
val cursor = downloadManager.query(query)


cursor.moveToFirst()


val bytesDownloaded = cursor.intValue(DownloadManager.COLUMN_BYTES_DOWNLOADED_SO_FAR)
val bytesTotal = cursor.intValue(DownloadManager.COLUMN_TOTAL_SIZE_BYTES)


if (isSuccessful(cursor)) downloading.set(false)
           

cursor.close()


emit(DownloadingState.Downloading(bytesDownloaded, bytesTotal))


if (downloading.get()) delay(1000)
}
}.flowOn(Dispatchers.IO)

Some helpers/extensions

    private fun isSuccessful(cursor: Cursor) = status(cursor) == DownloadManager.STATUS_SUCCESSFUL
private fun status(cursor: Cursor) = cursor.intValue(DownloadManager.COLUMN_STATUS)
private fun Cursor.column(which: String) = this.getColumnIndex(which)
private fun Cursor.intValue(which: String): Int = this.getInt(column(which))


sealed class DownloadingState {
data class Downloading(val downloadedBytes: Int, val totalBytes: Int) : DownloadingState() {
val progress = if (totalBytes == 0) 0 else ((downloadedBytes * 100) / totalBytes)
}
object Failure : DownloadingState()
}