FragmentTransaction的commit和commitAllowingStateLoss的区别

标签：android开发   fragment   fragmenttransaction   commit   commitallowingstatel   

1、什么是FragmentTransaction？

使用Fragment时，可以通过用户交互来执行一些动作，比如增加、移除、替换等。

所有这些改变构成一个集合，这个集合被叫做一个transaction。

可以调用FragmentTransaction中的方法来处理这个transaction，并且可以将transaction存进由activity管理的back stack中，这样用户就可以进行fragment变化的回退操作。

可以这样得到FragmentTransaction类的实例：

FragmentManager  mFragmentManager = getSupportFragmentManager();
FragmentTransaction  mFragmentTransaction = mFragmentManager.beginTransaction();

2、commit和executePendingTransactions的区别

3、问什么在存储状态之后调用commit会报异常？

/**
     * Return the FragmentManager for interacting with fragments associated
     * with this activity.
     */
    public FragmentManager getSupportFragmentManager() {
        return mFragments;
    }

/**
 * Container for fragments associated with an activity.
 */
final class FragmentManagerImpl extends FragmentManager {
    
    ........


    @Override
    public FragmentTransaction beginTransaction() {
        return new BackStackRecord(this);
    }


    ........


    }

/**
 * @hide Entry of an operation on the fragment back stack.
 */
final class BackStackRecord extends FragmentTransaction implements
        FragmentManager.BackStackEntry, Runnable {


	..........
	public int commit() {
        return commitInternal(false);
    }


    public int commitAllowingStateLoss() {
        return commitInternal(true);
    }


	int commitInternal(boolean allowStateLoss) {
        if (mCommitted) throw new IllegalStateException("commit already called");
        if (FragmentManagerImpl.DEBUG) Log.v(TAG, "Commit: " + this);
        mCommitted = true;
        if (mAddToBackStack) {
            mIndex = mManager.allocBackStackIndex(this);
        } else {
            mIndex = -1;
        }
        mManager.enqueueAction(this, allowStateLoss);
        return mIndex;
    }
	..........


}

/**
 * @hide Entry of an operation on the fragment back stack.
 */
final class BackStackRecord extends FragmentTransaction implements
        FragmentManager.BackStackEntry, Runnable {


	..........
	public int commit() {
        return commitInternal(false);
    }


    public int commitAllowingStateLoss() {
        return commitInternal(true);
    }


	int commitInternal(boolean allowStateLoss) {
        if (mCommitted) throw new IllegalStateException("commit already called");
        if (FragmentManagerImpl.DEBUG) Log.v(TAG, "Commit: " + this);
        mCommitted = true;
        if (mAddToBackStack) {
            mIndex = mManager.allocBackStackIndex(this);
        } else {
            mIndex = -1;
        }
        mManager.enqueueAction(this, allowStateLoss);
        return mIndex;
    }
	..........


}

private void checkStateLoss() {
        if (mStateSaved) {
            throw new IllegalStateException(
                    "Can not perform this action after onSaveInstanceState");
        }
        if (mNoTransactionsBecause != null) {
            throw new IllegalStateException(
                    "Can not perform this action inside of " + mNoTransactionsBecause);
        }
    }

FragmentTransaction的commit和commitAllowingStateLoss的区别,布布扣,bubuko.com

FragmentTransaction的commit和commitAllowingStateLoss的区别

标签：android开发   fragment   fragmenttransaction   commit   commitallowingstatel   

原文地址：http://blog.csdn.net/stoppig/article/details/31776607