根据公开片段更改选项在动作条菜单图标 [英] Changing options menu icon in actionbar depending on an open Fragment

问题描述

我有这个项目在我的选项菜单：

I have this item in my options menu:

<item
    android:id="@+id/opt_mnu_action"
    android:icon="@android:drawable/ic_dialog_info"
    android:orderInCategory="1"
    android:showAsAction="ifRoom"
    android:title="New">
</item>

本身在主FragmentActivity创建的菜单。我想改变这个项目的图标编程取决于开放的片段，很明显，当用户点击这个按钮有不同的动作。我试过几件事情要做到这一点，但毫无效果。我想的最后一件事是在我的片段的方法onCreateView这code：

The menu itself created in main FragmentActivity. I want to change this item's icon programmatically depending on the open Fragment and, obviously, have different actions when the user hits this button. I tried several things to do that, but nothing worked. The last thing I tried was this code in my Fragment's onCreateView method:

MenuItem mi = (MenuItem) view.findViewById(R.id.opt_mnu_action);
mi.setIcon(R.drawable.ico_1);

但我的应用程序崩溃。那么，有没有办法做到这一点？

But my app crashed. So is there a way to do that?

的**更新**

**UPDATE**

下面就是我想现在要做的，都在我的主要主FragmentActivity：
首先我有一个菜单项action_button; 在我的层次视图。然后在我的 onCreateOptionsMenu 方法我将它实例：

Here's what I'm trying to do now, all in my main main FragmentActivity: First of all I have a MenuItem action_button; in my hierarchy view. Then in my onCreateOptionsMenu method I instantiate it:

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    MenuInflater inflater = getMenuInflater();
    inflater.inflate(R.menu.options_menu, menu);
    action_button = menu.findItem(R.id.opt_mnu_action);
    return super.onCreateOptionsMenu(menu);
}

然后我创造了这个功能根据打开的标签更改图标：

Then I created this function to change the icon according to the open tab:

public void change_action_button_icon(int tab_position)
{
    switch(tab_position)
    {
    case 0:
        action_button.setIcon(R.drawable.ico_1);
        break;
    case 1:
        action_button.setIcon(R.drawable.ico_2);
        break;
    case 2:
        action_button.setIcon(R.drawable.ico_3);
        break;
    }
    invalidateOptionsMenu();
}

和我把它在我的 onTabSelected 方法：

public void onTabSelected(ActionBar.Tab tab,
        FragmentTransaction fragmentTransaction) {
    mViewPager.setCurrentItem(tab.getPosition());
    setTab_position(tab.getPosition());
    change_action_button_icon(tab.getPosition());
}

但是，一旦我开始我的应用程序 - 它崩溃。我得到 NullPointerException异常错误在这行：

action_button.setIcon(R.drawable.ico_1);

我的猜测 - 这是因为图标变化前的要求action_button 被实例化。但我不知道怎么去克服它...

My guess - it happens because the icon change was requested before the action_button was instantiated. But I don't know how to overcome it...

推荐答案

使用此去的菜单项的引用：

Use this to get a reference to the menu item:

    menu.findItem(resourceId).setIcon(drawableId);

您必须把code改变onCreateOptionsMenu（）图标。

You have to put the code to change the icon in onCreateOptionsMenu().

请参考下面我举的例子：

Please refer to my example below:

    public boolean onCreateOptionsMenu(Menu menu) {
    super.onCreateOptionsMenu(menu);

    getMenuInflater().inflate(R.menu.option_menu, menu);

    if (needToChangeMenuItem){

        menu.findItem(resourceId).setIcon(drawableId);
    }

    manageMenuIcon(menu);

    needToChangeMenuItem = false;


    return true;
}


    public void manageMenuIcon(Menu menu){
    if (bluetoothIconOn){
        menu.findItem(R.id.secure_connect_scan).setIcon(R.drawable.bluetoothon);
    } else
        menu.findItem(R.id.secure_connect_scan).setIcon(R.drawable.bluetoothoff);

    if (gpsIconOn)
        menu.findItem(R.id.gps).setIcon(R.drawable.gps);
    else
        menu.findItem(R.id.gps).setVisible(false);

    if (slipAndDropIconOn)
        menu.findItem(R.id.fall).setIcon(R.drawable.fall);
    else
        menu.findItem(R.id.fall).setVisible(false);

    if (fesConnectIconOn)
        menu.findItem(R.id.fesConnection).setIcon(R.drawable.fesconnect);
    else
        menu.findItem(R.id.fesConnection).setVisible(false);


}


    public void changeMenuItem(int resId, int draId){


    needToChangeMenuItem = true;
    resourceId = resId;
    drawableId = draId;

    invalidateOptionsMenu();        


}

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