妙用AlertActivity的mAlertParams 和 mAlert

final AlertController.AlertParams p = mAlertParams;
        p.mCursor = mCursor;
        p.mOnClickListener = mRingtoneClickListener;
        p.mLabelColumn = MediaStore.Audio.Media.TITLE;
        p.mIsSingleChoice = true;
        p.mOnItemSelectedListener = this;
        p.mPositiveButtonText = getString(com.android.internal.R.string.ok);
        p.mPositiveButtonListener = this;
        p.mNegativeButtonText = getString(com.android.internal.R.string.cancel);
        p.mPositiveButtonListener = this;
        p.mOnPrepareListViewListener = this;

        p.mTitle = intent.getCharSequenceExtra(RingtoneManager.EXTRA_RINGTONE_TITLE);
        if (p.mTitle == null) {
            p.mTitle = getString(com.android.internal.R.string.ringtone_picker_title);
        }   

        setupAlert();

        if (mClickedPos == POS_UNKNOWN) {
            mOkButton = mAlert.getButton(DialogInterface.BUTTON_POSITIVE);
            if (null != mOkButton) {
                mOkButton.setEnabled(false);
            }   
        }   

        Window w = getWindow();
        WindowManager.LayoutParams attrs = w.getAttributes();
        attrs.width = WindowManager.LayoutParams.MATCH_PARENT;
        w.setAttributes(attrs);