DownlaodManager note

android 5.1.1 (22)，Honor:CHM-TL00H:手机上系统数据库缺少字段造成下载失败

java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String android.net.Uri.getLastPathSegment()' on a null object reference
	at android.app.DownloadManager.enqueue(DownloadManager.java:950)

DownloadManager disable造成下载失败

禁用／开启DownloadManager方法：设置－>引用程序->下载管理器－>Enable/Disable

java.lang.IllegalArgumentException: Unknown URL content://downloads/my_downloads

源码分析

//ContentResolver.java文件中
   public final @Nullable Uri insert(@NonNull Uri url, @Nullable ContentValues values) {
       Preconditions.checkNotNull(url, "url");
       IContentProvider provider = acquireProvider(url);
       if (provider == null) {
       		//DownloadManager disable造成下载失败
           throw new IllegalArgumentException("Unknown URL " + url);
       }
       try {
           long startTime = SystemClock.uptimeMillis();
           //insert时数据库该手机上数据库缺少个字段造成return null
           Uri createdRow = provider.insert(mPackageName, url, values);
           long durationMillis = SystemClock.uptimeMillis() - startTime;
           maybeLogUpdateToEventLog(durationMillis, url, "insert", null /* where */);
           return createdRow;
       } catch (RemoteException e) {
           // Arbitrary and not worth documenting, as Activity
           // Manager will kill this process shortly anyway.
           return null;
       } finally {
           releaseProvider(provider);
       }
   }

需先判断DownloadManager是否可用，在进行下载

参考Gmail inbox做法,下载前检测DownloadManager是否可用，如果不可用提示用户DownloadManager is disabled. Please enable it.

how to enable android download manager

private static boolean isEnableDownloadManager(Context context) {
        ApplicationInfo ai = null;
        try {
            ai = context.getPackageManager().getApplicationInfo("com.android.providers.downloads", 0);
        } catch (PackageManager.NameNotFoundException e) {
            return false;
        }

        return ai.enabled;
    }

Url不合法会崩溃,需要检查Url

Uri resource = Uri.parse(apkPath);
DownloadManager.Request request;
//url不合法会崩溃
request = new DownloadManager.Request(resource);

使用URLUtil.isValidUrl(url)来判断url是否合法（www.qq.com这种是不合法的，必需有http://等）

check url is valid

try catch 会不会影响性能

在不抛出异常等情况下，不会影响性能。try catch范围等大小也不会影响性能，只是影响代码可读性。