之前專案有需求做app內更新，試了很多都不行，最後自己結合網上找到的資料，自己寫了一個工具類，相容Android7.0，有問題的話歡迎留言。二話不說直接上程式碼吧

/**
 * 2018-01-09 haoshiwei
 * app內部更新的工具類
 * 相容7.0
 */
public class DownloadUtils {
    //下載器
private DownloadManager downloadManager;
//上下文
private Context mContext;
//下載的ID
private long downloadId;
    public DownloadUtils(Context context){
        this
 
.mContext = context;
}

    //下載apk
public void downloadAPK(String url, String name) {

        //建立下載任務
DownloadManager.Request request = new DownloadManager.Request(Uri.parse(url));
//行動網路情況下是否允許漫遊
request.setAllowedOverRoaming(false);
//在通知欄中顯示，預設就是顯示的
request.setNotificationVisibility(DownloadManager.Request.VISIBILITY_VISIBLE
 
);
request.setTitle("狐小狸");
request.setDescription("Apk Downloading");
request.setVisibleInDownloadsUi(true);
//設定下載的路徑
request.setDestinationInExternalPublicDir(Environment.DIRECTORY_DOWNLOADS , name);
//獲取DownloadManager
downloadManager = (DownloadManager) mContext.getSystemService(Context.DOWNLOAD_SERVICE
 
);
//將下載請求加入下載佇列，加入下載佇列後會給該任務返回一個long型的id，通過該id可以取消任務，重啟任務、獲取下載的檔案等等
downloadId = downloadManager.enqueue(request);
//註冊廣播接收者，監聽下載狀態
mContext.registerReceiver(receiver,
                new IntentFilter(DownloadManager.ACTION_DOWNLOAD_COMPLETE));
}

    //廣播監聽下載的各個狀態
private BroadcastReceiver receiver = new BroadcastReceiver() {
        @Override
public void onReceive(Context context, Intent intent) {
            checkStatus();
}
    };
//檢查下載狀態
private void checkStatus() {
        DownloadManager.Query query = new DownloadManager.Query();
//通過下載的id查詢
query.setFilterById(downloadId);
Cursor c = downloadManager.query(query);
        if (c.moveToFirst()) {
            int status = c.getInt(c.getColumnIndex(DownloadManager.COLUMN_STATUS));
            switch (status) {
                 //下載暫停
case DownloadManager.STATUS_PAUSED:
                    break;
//下載延遲
case DownloadManager.STATUS_PENDING:
                    break;
//正在下載
case DownloadManager.STATUS_RUNNING:
                    break;
//下載完成
case DownloadManager.STATUS_SUCCESSFUL:
                    //下載完成安裝APK
installAPK();
                    break;
//下載失敗
case DownloadManager.STATUS_FAILED:
                    Toast.makeText(mContext, "下載失敗", Toast.LENGTH_SHORT).show();
                    break;
}
        }
        c.close();
}

//下載到本地後執行安裝
private void installAPK() {
    //獲取下載檔案的Uri
Uri downloadFileUri = downloadManager.getUriForDownloadedFile(downloadId);
    if (downloadFileUri != null) {
        Intent intent= new Intent(Intent.ACTION_VIEW);
intent.setDataAndType(downloadFileUri, "application/vnd.android.package-archive");
intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
mContext.startActivity(intent);
mContext.unregisterReceiver(receiver);
}
}

/**
 * 7.0相容
 */
private void installAPK() {
    File apkFile =
            new File(Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS), "huxiaoli.apk");
Intent intent = new Intent(Intent.ACTION_VIEW);
intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
    if (Build.VERSION.SDK_INT >= 24) {
        Uri apkUri = FileProvider.getUriForFile(mContext, mContext.getPackageName() + ".provider", apkFile);
intent.addFlags(Intent.FLAG_GRANT_READ_URI_PERMISSION);
intent.setDataAndType(apkUri, "application/vnd.android.package-archive");
} else {
        intent.setDataAndType(Uri.fromFile(apkFile), "application/vnd.android.package-archive");
}
    mContext.startActivity(intent);
}

<provider
android:name="android.support.v4.content.FileProvider"
android:authorities="你的包名.provider"
android:exported="false"
android:grantUriPermissions="true">
    <meta-data
android:name="android.support.FILE_PROVIDER_PATHS"
android:resource="@xml/provider_paths"/>
</provider>

<?xml version="1.0" encoding="utf-8"?>
<resources xmlns:android="http://schemas.android.com/apk/res/android">
    <paths>
        <external-path
name="download"
path=""/>
    </paths>
</resources>