等待直到su中的命令完成 [英] Wait until a command in su finishes

问题描述

我正在Android中运行一个 su 进程，该进程本身在每次用户摇动手机时都会运行screencap实用程序(/system/bin/screencap ).

I am running a su process in Android which itself runs the screencap utility (/system/bin/screencap) every time the user shakes their phone.

我想等待每个屏幕截图完成，然后再允许用户通过摇动手机拍摄另一个屏幕截图.但是，使用 process.waitFor()对我不起作用，因为我不想关闭 su 进程并为每个屏幕截图重新打开它(因为它会提示SuperUser应用的举杯，这会干扰屏幕截图)

I want to wait for each screencap to finish before I allow the user to take another screencap by shaking the phone. However, using process.waitFor() doesn't work for me because I don't want to close the su process and reopen it for each screencap (because it would prompt the SuperUser app's toast, which interferes with screencaps)

到目前为止，我有:

在服务的 onCreate()中:

p = Runtime.getRuntime().exec("su");
os = p.getOutputStream();

在震动监听器处理程序中:

in the shake listener handler:

if (isReady) {
  isReady = false;
  String cmd = "/system/bin/screencap -p " + nextScreenshotFullPath + "\n";
  os.write(cmd.getBytes("ASCII"));
  os.flush();

  [INSERT MAGIC HERE]
  isReady = true;

  Bitmap bm = BitmapFactory.decodeFile(nextScreenshotFullPath);
  // Do something with bm
}

我正在寻找[INSERT MAGIC HERE]的地方-等待 screencap 完成的那段代码.

Where [INSERT MAGIC HERE] is what I'm looking for - the piece of code that would wait until screencap finishes.

推荐答案

我找到了一种方法！我使用shell命令 echo -n 0 ( -n 以防止换行)回显单个字符(例如 0 )，然后读取回来了.在 screencap 命令完成并且 InputStream#read()方法将阻塞之前，shell才会打印该字符，直到它可以读取该字符为止.代码说话:

I found a way! I echo a single character (say, 0) using the shell command echo -n 0 (-n to prevent a newline) and then reading it back. The shell won't print the character until after the screencap command is finished and the InputStream#read() method will block until it can read that character... or in code speak:

在服务的onCreate()中:

in service's onCreate():

p = Runtime.getRuntime().exec("su");
os = p.getOutputStream();
is = p.getInputStream(); // ADDED THIS LINE //

在震动监听器处理程序中:

in the shake listener handler:

if (isReady) {
  isReady = false;
  String cmd = "/system/bin/screencap -p " + nextScreenshotFullPath + "\n";
  os.write(cmd.getBytes("ASCII"));
  os.flush();

  // ADDED LINES BELOW //
  cmd = "echo -n 0\n";
  os.write(cmd.getBytes("ASCII"));
  os.flush();
  is.read();
  // ADDED LINES ABOVE //

  isReady = true;

  Bitmap bm = BitmapFactory.decodeFile(nextScreenshotFullPath);
  // Do something with bm
}

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