آموزش: شیوه درست صدازدن Superclass ها در Activity

شیوه درست صدا زدن Superclass ها در Activity اندروید:

// Called after onCreate has finished, use to restore UI state
@Override
public void onRestoreInstanceState(Bundle savedInstanceState)
{
    super.onRestoreInstanceState(savedInstanceState); // Always call the superclass method at FIRST.

    // Restore UI state from the savedInstanceState.
    // This bundle has also been passed to onCreate.
    // Will only be called if the Activity has been
    // killed by the system since it was last visible.
}

// Called before subsequent visible lifetimes for an activity process.
@Override
public void onRestart()
{
    super.onRestart(); // Always call the superclass method at FIRST.

    // Load changes knowing that the Activity has already
    // been visible within this process.
}

// Called at the start of the visible lifetime.
@Override
public void onStart()
{
    super.onStart(); // Always call the superclass method at FIRST.

    // Apply any required UI change now that the Activity is visible.
}

// Called at the start of the active lifetime.
@Override
public void onResume()
{
    // Resume any paused UI updates, threads, or processes required
    // by the Activity but suspended when it was inactive.

    super.onResume(); // Always call the superclass method at LAST.
}

// Called to save UI state changes at the end of the active lifecycle.
@Override
public void onSaveInstanceState(Bundle savedInstanceState)
{
    // Save UI state changes to the savedInstanceState.
    // This bundle will be passed to onCreate and
    // onRestoreInstanceState if the process is
    // killed and restarted by the run time.
    super.onSaveInstanceState(savedInstanceState); // Always call the superclass method at LAST.
}

// Called at the end of the active lifetime.
@Override
public void onPause()
{
    // Suspend UI updates, threads, or CPU intensive processes
    // that don't need to be updated when the Activity isn't
    // the active foreground Activity.
    super.onPause(); // Always call the superclass method at LAST.
}

// Called at the end of the visible lifetime.
@Override
public void onStop()
{
    super.onStop(); // Always call the superclass method at FIRST.

    // Suspend remaining UI updates, threads, or processing
    // that aren't required when the Activity isn't visible.
    // Persist all edits or state changes
    // as after this call the process is likely to be killed.
}

// Sometimes called at the end of the full lifetime.
@Override
public void onDestroy()
{
    // Clean up any resources including ending threads,
    // closing database connections etc.

    super.onDestroy(); // Always call the superclass method at LAST.
}

خلاصه مطب: در متد های onRestoreInstanceState، onStop, onRestart, onStart، ابتدا باید Superclass صدا زده بشه و بعد کدهای شما قرار بگیره. اما در متدهای onDestroy, onPause, onSaveInstanceState, onResume ابتدا باید کدهای شما قرار بگیره و بعد متد Superclass صدا زده بشه.

عدم رعایت این اولویت ها گاهی باعث کندی، crash کردن، memory leak، ناهماهنگی در UI، باگهای DataSaving و امثالش میشه... پس حتماً رعایت کنید.

(شاید درصد کمی از برنامه ها باشند که از این قائده پیروی نمی کنند، اما با آگاهی کامل از محتوا و مکانیسم Superclass ها.)

منبع: پروفسور Andrew T. Campbell (و گوگل)

http://www.cs.dartmouth.edu/~campbell/cs65/lecture05/lecture05.html