在Android的ImageView和进度执行图像下载

问题描述

我需要在的ImageView 来下载图像。我想用一个进度来告诉程序下载图像的用户。如果程序无法在30秒下载图像，程序会使用吐司 / AlertDialog 来通知用户并退出。

I need to download an image in an ImageView. I want to use a ProgressBar to tell the user that the program is downloading images. If the program can't download the image in 30sec, the program will use a Toast/AlertDialog to notify the user and exit.

我怎样才能实现这个功能呢？任何人都可以给我就如何建立框架一些建议吗？我能完成的细节。我需要线程？ / AsyncTask的？

How can I implement this function? Could anyone give me some advice on how to build the framework? I can complete the details. Do I need thread? / AsyncTask?

推荐答案

是的，你需要下载的AsyncTask图像（我假设你是从网址下载）。
有效地实现自己的功能，这就是你需要做的：

Yes, you do need to download the image in AsyncTask (I am assuming that you are downloading from URL).Effectively to achieve your functionality this is what you need to do:

1. 创建的AsyncTask下载图像（实现doInBackground下载（）），也有一个布尔值（比如isImageDownloaded）来跟踪如果图像是postExecute成功下载（）。不要忘了启动下载之前还显示进度条


2. 执行您的AsyncTask开始下载


3. 创建android.os.CountDownTimer延伸至倒数30秒


4. 在法onFinish（）检查您跟踪布尔值，如果是假的，那么你取消AsyncTask的扔，你预期的面包/对话框

下面是伪code /什么我上面提到的步骤骨架（没有检查语法，所以我对任何错误道歉）

Below is the pseudocode/skeleton of what the steps that I mentioned above (didn't check for syntax, so I apologize for any error)

    public void downloadAndCheck() {
                AsyncTask downloadImageAsyncTask =
                    new AsyncTask() {

                    @Override
                    protected Boolean doInBackground(Void... params) {
                        // download image here, indicate success in the return boolean
                    }

                    @Override
                    protected void onPostExecute(Boolean isConnected) {
                        // set the boolean result in a variable
                        // remove the progress bar
                    }
                };

                try {
                    downloadImageAsyncTask.execute();
                } catch(RejectedExecutionException e) {
                    // might happen, in this case, you need to also throw the alert
                    // because the download might fail
                }


                // note that you could also use other timer related class in Android aside from this CountDownTimer, I prefer this class because I could do something on every interval basis
                // tick every 10 secs (or what you think is necessary)
                CountDownTimer timer = new CountDownTimer(30000, 10000) {

                    @Override
                    public void onFinish() {
                        // check the boolean, if it is false, throw toast/dialog
                    }

                    @Override
                    public void onTick(long millisUntilFinished) {
                        // you could alternatively update anything you want every tick of the interval that you specified
                    }

                };

                timer.start()
        }

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