尝试使用支持库在Action Bar中使用自定义微调器

Question

我正在尝试制作一个带有自定义微调器的Android应用程序，其中包含列表中每个项目的图像图标。此微调器将显示在应用程序的操作栏中。我正在使用android-support-v7-appcompat库来确保操作栏显示在Android 2.2及更高版本中。

当我在android 3.0及更高版本中运行应用程序时，每件事都运行良好。但是当我点击android 2.2和2.3中的微调器时，应用程序崩溃了。好像旋转器没有正确充气。

这是我的android 2.3错误日志：

02-09 13:55:12.289: E/AndroidRuntime(8624): FATAL EXCEPTION: main
02-09 13:55:12.289: E/AndroidRuntime(8624): java.lang.NullPointerException
02-09 13:55:12.289: E/AndroidRuntime(8624):     at android.support.v7.internal.widget.ListPopupWindow$DropDownListView.measureHeightOfChildrenCompat(ListPopupWindow.java:1317)
02-09 13:55:12.289: E/AndroidRuntime(8624):     at android.support.v7.internal.widget.ListPopupWindow.buildDropDown(ListPopupWindow.java:1062)
02-09 13:55:12.289: E/AndroidRuntime(8624):     at android.support.v7.internal.widget.ListPopupWindow.show(ListPopupWindow.java:514)
02-09 13:55:12.289: E/AndroidRuntime(8624):     at android.support.v7.internal.widget.SpinnerICS$DropdownPopup.show(SpinnerICS.java:758)
02-09 13:55:12.289: E/AndroidRuntime(8624):     at android.support.v7.internal.widget.SpinnerICS.performClick(SpinnerICS.java:443)
02-09 13:55:12.289: E/AndroidRuntime(8624):     at android.view.View$PerformClick.run(View.java:9080)
02-09 13:55:12.289: E/AndroidRuntime(8624):     at android.os.Handler.handleCallback(Handler.java:587)
02-09 13:55:12.289: E/AndroidRuntime(8624):     at android.os.Handler.dispatchMessage(Handler.java:92)
02-09 13:55:12.289: E/AndroidRuntime(8624):     at android.os.Looper.loop(Looper.java:130)
02-09 13:55:12.289: E/AndroidRuntime(8624):     at android.app.ActivityThread.main(ActivityThread.java:3687)
02-09 13:55:12.289: E/AndroidRuntime(8624):     at java.lang.reflect.Method.invokeNative(Native Method)
02-09 13:55:12.289: E/AndroidRuntime(8624):     at java.lang.reflect.Method.invoke(Method.java:507)
02-09 13:55:12.289: E/AndroidRuntime(8624):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:867)
02-09 13:55:12.289: E/AndroidRuntime(8624):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:625)
02-09 13:55:12.289: E/AndroidRuntime(8624):     at dalvik.system.NativeStart.main(Native Method)

我用过这两个类来制作自定义微调器： 1）SpinnerNavItem.java：

package com.hpubts50.hpubustracker.model;

public class SpinnerNavItem {

    private String title;
    private int icon;

    public SpinnerNavItem(String title, int icon){
        this.title = title;
        this.icon = icon;
    }

    public String getTitle(){
        return this.title;
    }

    public int getIcon(){
        return this.icon;
    }

}

2）BusNavigation.java - 它是一个适配器类：

package com.hpubts50.hpubustracker.adapter;

import java.util.ArrayList;

import android.content.Context;
import android.support.v7.app.ActionBarActivity;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.ImageView;
import android.widget.TextView;

import com.hpubts50.hpubustracker.R;
import com.hpubts50.hpubustracker.model.SpinnerNavItem;

public class BusNavigation extends BaseAdapter {
    private ImageView busIcon;
    private TextView busTitle;
    private ArrayList<SpinnerNavItem> spinnerNavItem;
    private Context context;

    public BusNavigation(Context context, ArrayList<SpinnerNavItem> spinnerNavItem) {
        this.spinnerNavItem = spinnerNavItem;
        this.context = context;
    }

    @Override
    public int getCount() {
        return spinnerNavItem.size();
    }

    @Override
    public Object getItem(int index) {
        return spinnerNavItem.get(index);
    }

    @Override
    public long getItemId(int position) {
        return position;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        if (convertView == null) {
            LayoutInflater mInflater = (LayoutInflater) context.getSystemService(ActionBarActivity.LAYOUT_INFLATER_SERVICE);
            convertView = mInflater.inflate(R.layout.bus_names, null);
        }

        busIcon = (ImageView) convertView.findViewById(R.id.busIcon);
        busTitle = (TextView) convertView.findViewById(R.id.busTitle);

        busIcon.setImageResource(spinnerNavItem.get(position).getIcon());
        busIcon.setVisibility(View.GONE);
        busTitle.setText(spinnerNavItem.get(position).getTitle());
        return convertView;
    }

    @Override
    public View getDropDownView(int position, View convertView, ViewGroup parent) {
        if (convertView == null) {
            LayoutInflater mInflater = (LayoutInflater) context.getSystemService(ActionBarActivity.LAYOUT_INFLATER_SERVICE);
            convertView = mInflater.inflate(R.layout.bus_names, null);
        }

        busIcon = (ImageView) convertView.findViewById(R.id.busIcon);
        busTitle = (TextView) convertView.findViewById(R.id.busTitle);

        busIcon.setImageResource(spinnerNavItem.get(position).getIcon());
        busTitle.setText(spinnerNavItem.get(position).getTitle());
        return convertView;
    }

}

这是我的MainActivity.java：

package com.hpubts50.hpubustracker;

import java.util.ArrayList;

import android.annotation.SuppressLint;
import android.os.Bundle;
import android.support.v7.app.ActionBar;
import android.support.v7.app.ActionBar.OnNavigationListener;
import android.support.v7.app.ActionBarActivity;
import android.view.Menu;
import android.widget.Toast;

import com.google.android.gms.maps.GoogleMap;
import com.google.android.gms.maps.SupportMapFragment;
import com.hpubts50.hpubustracker.adapter.BusNavigation;
import com.hpubts50.hpubustracker.model.SpinnerNavItem;

public class MainActivity extends ActionBarActivity implements OnNavigationListener {
    GoogleMap BusMap;
    private ActionBar actionBar;
    private ArrayList<SpinnerNavItem> navSpinner;
    private BusNavigation busAdapter;

    @SuppressLint("NewApi")
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        // Configuring Action Bar to support list adapter
        showListView();

        // Converting values to pixels from density pixels
        final int paddingUP_dp = 60;
        final int paddingDOWN_dp = 70;
        final float scale = getResources().getDisplayMetrics().density;
        int paddingUP_px = (int) (paddingUP_dp * scale + 0.5f);
        int paddingDOWN_px = (int) (paddingDOWN_dp * scale + 0.5f);

        // Changing positions for the map zoom controls and compass
        BusMap = ((SupportMapFragment) getSupportFragmentManager().findFragmentById(R.id.bus_map)).getMap();
        BusMap.setPadding(0, paddingUP_px, 0, paddingDOWN_px);

    }

    private void showListView() {
        actionBar = getSupportActionBar();
        actionBar.setDisplayShowTitleEnabled(false);
        actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_LIST);

        navSpinner = new ArrayList<SpinnerNavItem>();
        navSpinner.add(new SpinnerNavItem("All", R.drawable.ic_action_about));
        navSpinner.add(new SpinnerNavItem("Nandi", R.drawable.ic_action_about));
        navSpinner.add(new SpinnerNavItem("Alaknanda", R.drawable.ic_action_about));
        navSpinner.add(new SpinnerNavItem("Other Buses", R.drawable.ic_action_about));

        busAdapter = new BusNavigation(getApplicationContext(), navSpinner);

        actionBar.setListNavigationCallbacks(busAdapter, this);
    }

    @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);
        return true;
    }

    @Override
    public boolean onNavigationItemSelected(int itemPosition, long itemId) {
        switch (itemPosition) {
        case 1:
            Toast.makeText(getApplicationContext(), "Its Working ...", Toast.LENGTH_SHORT).show();
            break;
        }
        return false;
    }

}

我已按照本教程制作此自定义微调器：tutorial link

Answer 1

最后经过大约6个小时的努力，我终于找到了解决问题的方法：

这一行：

convertView = mInflater.inflate(R.layout.bus_names, null);

将替换为此行：

convertView = mInflater.inflate(R.layout.bus_names, parent, false);