为什么我不能在MenuItem

问题描述

我一直想尝试简单地更改此MenuItem图标的透明度达数小时之久……我不确定该怎么做。我能够成功调用图标上的setEnable()，这意味着无法访问它。它必须与图标本身有关。我使用的是“基本活动模板”随附的标准“材质”主题，一种样式或主题会阻止我以编程方式更改它吗？我从一个片段中呼叫onPrepareOptionsMenu，这可能是问题吗？这是我的代码：

@Override
public void onCreateOptionsMenu(Menu menu,MenuInflater inflater) {
    super.onCreateOptionsMenu(menu,inflater);

    // top menu (action bar)
    inflater.inflate(R.menu.menu_searches,menu);

    // bottom menu (the one I am having an issue with)
    Menu bottomMenu = toolbarBottom.getMenu();

    // the MenuItem I am trying to call "setAlpha()" on
    deleteMenuItem = bottomMenu.findItem(R.id.action_delete);

    for (int itemIndex = 0; itemIndex < bottomMenu.size(); itemIndex++) {
        bottomMenu.getItem(itemIndex).setOnMenuItemClickListener(new
            MenuItem.OnMenuItemClickListener() {
            @Override
            public boolean onMenuItemClick(MenuItem item) {
                return onOptionsItemSelected(item);
            }
        });
    }
}

@Override
    public void onPrepareOptionsMenu(Menu menu) {
        super.onPrepareOptionsMenu(menu);

        if (itemsChecked > 0) {
            deleteMenuItem.setEnabled(true);
            
            /* I have also tried "delete.getIcon().mutate().setAlpha(255);" -
- but I do not have another instance of the icon so I don't think I need to -
- call "mutate()". It didn't work anyways */
            deleteMenuItem.getIcon().setAlpha(255);

        } else {
            deleteMenuItem.setEnabled(false);
            deleteMenuItem.getIcon().setAlpha(5);
        }
    }

解决方法

menu.findItem()太迟了，在onPrepareOptionsMenu(Menu menu)中调用它会带来糟糕的用户体验。最好在创建菜单时获取一次MenuItem对象，然后每次菜单出现在屏幕上时都调用setAlpha。你可以尝试

MenuItem mDynamicMenuItem;

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.main,menu);
    // Get dynamic menu item
    mDynamicMenuItem = menu.findItem(R.id.menu_item);
    return true;
}

@Override
public boolean onPrepareOptionsMenu(Menu menu) {
    super.onPrepareOptionsMenu(menu);
    // Here is just a good place to update item
    MenuItem delete = mDynamicMenuItem.findItem(R.id.action_delete);

    if (itemsChecked > 0) {
        delete.setEnabled(true);
        delete.getIcon().setAlpha(255);

    } else {
        delete.setEnabled(false);
        delete.getIcon().mutate().setAlpha(5);
        delete.getIcon().setAlpha(5);
    }
    return true;
}