AsyncTask 中的无效索引 3 大小为 3

Question

我正在使用AsyncTask 来检查Fragment 是否已被替换。发生此错误时会出现问题，因为我没有使用ArrayList。 崩溃很少发生，并且发生在循环中的 AsyncTask 内。

这是错误：

java.lang.RuntimeException: An error occurred while executing doInBackground()
    at android.os.AsyncTask$3.done(AsyncTask.java:309)
    at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:354)
    at java.util.concurrent.FutureTask.setException(FutureTask.java:223)
    at java.util.concurrent.FutureTask.run(FutureTask.java:242)
    at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:234)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1113)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:588)
    at java.lang.Thread.run(Thread.java:818)
  Caused by: java.lang.IndexOutOfBoundsException: Invalid index 3, size is 3
    at java.util.ArrayList.throwIndexOutOfBoundsException(ArrayList.java:255)
    at java.util.ArrayList.get(ArrayList.java:308)
    at android.support.v4.app.FragmentManagerImpl.findFragmentById(FragmentManager.java:1446)
    at com.runator.ui.newdesign.MainActivity$WaitForChangeFragment.doInBackground(MainActivity.java:1035)
    at com.runator.ui.newdesign.MainActivity$WaitForChangeFragment.doInBackground(MainActivity.java:1027)
    at android.os.AsyncTask$2.call(AsyncTask.java:295)

这是发生错误的代码：

@Override
protected String doInBackground(String... params) {
    Fragment auxCurrentFragment = getSupportFragmentManager().findFragmentById(ID_FRAME_LAYOUT);

    while (auxCurrentFragment instanceof FilterNavigationFragment) {
        auxCurrentFragment = getSupportFragmentManager().findFragmentById(ID_FRAME_LAYOUT);
    }

    return "Executed";

}

只有我这样说： auxCurrentFragment = getSupportFragmentManager().findFragmentById(ID_FRAME_LAYOUT);

如果有任何想法请帮助我，在此先感谢。

Answer 1

看起来问题出在 supportFragmentMannager 中：

 public Fragment findFragmentById(int id) {
    if (mAdded != null) {
        // First look through added fragments.
        for (int i=mAdded.size()-1; i>=0; i--) {
            Fragment f = mAdded.get(i);
            if (f != null && f.mFragmentId == id) {
                return f;
            }
        }
    }
    if (mActive != null) {
        // Now for any known fragment.
        for (int i=mActive.size()-1; i>=0; i--) {
            Fragment f = mActive.get(i);
            if (f != null && f.mFragmentId == id) {
                return f;
            }
        }
    }
    return null;
}

如果您在主线程中调用findFragmentByIdnot，则片段的计数可能会在调用期间更改。您可以尝试在主线程中调用该方法。

您可以使用YourActivity.this.runOnUiThread 或任一处理程序：

        new AsyncTask<Void, String, String>() {
        @Override
        protected String doInBackground(Void... params) {
            final int ID_FRAME_LAYOUT = 0;
            final Fragment[] auxCurrentFragment = {getSupportFragmentManager().findFragmentById(ID_FRAME_LAYOUT)};

            while (auxCurrentFragment[0] instanceof FilterNavigationFragment) {
                YourActivity.this.runOnUiThread(new Runnable() {
                    @Override
                    public void run() {
                        auxCurrentFragment[0] = getSupportFragmentManager().findFragmentById(ID_FRAME_LAYOUT);
                    }
                });
                try {
                    Thread.sleep(500);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }

            return "Executed";
        }
    };