只是一个扩展，如果有人需要一个库，那么这可能会有所帮助。感谢Raghav

It's worth noting that if you use the DownloadManager to kick off your download, be sure to save it to an external location e.g. setDestinationInExternalFilesDir(c, null, "<your name here>).apk";. The intent with a package-archive type doesn't appear to like the content: scheme used with downloads to an internal location, but does like file:. (Trying to wrap the internal path into a File object and then getting the path doesn't work either, even though it results in a file: url, as the app won't parse the apk; looks like it must be external.)

例子:

int uriIndex = cursor.getColumnIndex(DownloadManager.COLUMN_LOCAL_URI);
String downloadedPackageUriString = cursor.getString(uriIndex);
File mFile = new File(Uri.parse(downloadedPackageUriString).getPath());
Intent promptInstall = new Intent(Intent.ACTION_VIEW)
        .setDataAndType(Uri.fromFile(mFile), "application/vnd.android.package-archive")
        .addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
appContext.startActivity(promptInstall);

我只是想分享一个事实，我的apk文件保存到我的应用程序“数据”目录，我需要更改apk文件的权限，使其成为世界可读的，以便允许它以这种方式安装，否则系统会抛出“解析错误:解析包存在问题”;所以使用@Horaceman的解决方案，使:

File file = new File(dir, "App.apk");
file.setReadable(true, false);
Intent intent = new Intent(Intent.ACTION_VIEW);
intent.setDataAndType(Uri.fromFile(file), "application/vnd.android.package-archive");
startActivity(intent);

试试这个 -在舱单上填写:

uses-permission android:name="android.permission.INSTALL_PACKAGES"
        tools:ignore="ProtectedPermissions"

编写代码:

File sdCard = Environment.getExternalStorageDirectory();
String fileStr = sdCard.getAbsolutePath() + "/Download";// + "app-release.apk";
File file = new File(fileStr, "app-release.apk");
Intent promptInstall = new Intent(Intent.ACTION_VIEW).setDataAndType(Uri.fromFile(file),
                        "application/vnd.android.package-archive");

startActivity(promptInstall);

另一种解决方案不需要硬编码接收应用程序，因此更安全:

Intent intent = new Intent(Intent.ACTION_INSTALL_PACKAGE);
intent.setData( Uri.fromFile(new File(pathToApk)) );
startActivity(intent);

在Android Oreo及以上版本中，我们必须采用不同的方法以编程方式安装apk。

 private void installApkProgramatically() {


    try {
        File path = activity.getExternalFilesDir(Environment.DIRECTORY_DOWNLOADS);

        File file = new File(path, filename);

        Uri uri;

        if (file.exists()) {

            Intent unKnownSourceIntent = new Intent(Settings.ACTION_MANAGE_UNKNOWN_APP_SOURCES).setData(Uri.parse(String.format("package:%s", activity.getPackageName())));

            if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {

                if (!activity.getPackageManager().canRequestPackageInstalls()) {
                    startActivityForResult(unKnownSourceIntent, Constant.UNKNOWN_RESOURCE_INTENT_REQUEST_CODE);
                } else {
                    Uri fileUri = FileProvider.getUriForFile(activity.getBaseContext(), activity.getApplicationContext().getPackageName() + ".provider", file);
                    Intent intent = new Intent(Intent.ACTION_VIEW, fileUri);
                    intent.putExtra(Intent.EXTRA_NOT_UNKNOWN_SOURCE, true);
                    intent.setDataAndType(fileUri, "application/vnd.android" + ".package-archive");
                    intent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TASK | Intent.FLAG_ACTIVITY_NEW_TASK);
                    intent.addFlags(Intent.FLAG_GRANT_READ_URI_PERMISSION);
                    startActivity(intent);
                    alertDialog.dismiss();
                }

            } else if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.N) {

                Intent intent1 = new Intent(Intent.ACTION_INSTALL_PACKAGE);
                uri = FileProvider.getUriForFile(activity.getApplicationContext(), BuildConfig.APPLICATION_ID + ".provider", file);
                activity.grantUriPermission("com.abcd.xyz", uri, Intent.FLAG_GRANT_READ_URI_PERMISSION);
                activity.grantUriPermission("com.abcd.xyz", uri, Intent.FLAG_GRANT_WRITE_URI_PERMISSION);
                intent1.setDataAndType(uri,
                        "application/*");
                intent1.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
                intent1.addFlags(Intent.FLAG_GRANT_READ_URI_PERMISSION);
                intent1.addFlags(Intent.FLAG_GRANT_WRITE_URI_PERMISSION);
                startActivity(intent1);

            } else {
                Intent intent = new Intent(Intent.ACTION_VIEW);

                uri = Uri.fromFile(file);

                intent.setDataAndType(uri,
                        "application/vnd.android.package-archive");
                intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
                startActivity(intent);
            }
        } else {

            Log.i(TAG, " file " + file.getPath() + " does not exist");
        }
    } catch (Exception e) {

        Log.i(TAG, "" + e.getMessage());

    }
}

在Oreo及以上版本中，我们需要未知资源安装权限。所以在活动结果中，你必须检查结果的权限

    @Override
public void onActivityResult(int requestCode, int resultCode, @Nullable Intent data) {
    super.onActivityResult(requestCode, resultCode, data);
    switch (requestCode) {

        case Constant.UNKNOWN_RESOURCE_INTENT_REQUEST_CODE:
            switch (resultCode) {
                case Activity.RESULT_OK:
                    installApkProgramatically();

                    break;
                case Activity.RESULT_CANCELED:
                    //unknown resouce installation cancelled

                    break;
            }
            break;
    }
}