Question

我有使ListAdapters正常工作的经验，并且已经在线查看有关自定义适配器的教程以与GridView接口，但我似乎无法让我的工作正常工作。我在我的行上收到了NullPointerException：

image.setBackgroundColor(Color.GREEN);

我的活动和适配器如下： FixtureActivity：

package net.blakely.paul.Hyperion;

import android.os.Bundle;
import android.widget.GridView;
import com.actionbarsherlock.app.SherlockActivity;

public class FixtureActivity extends SherlockActivity {


    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.fixtures);
        FixtureItemAdapter fia = new FixtureItemAdapter(this, 6);
        GridView grids = (GridView) findViewById(R.id.grids);
        grids.setAdapter(fia);

        }

}

FixtureItemAdapter：

package net.blakely.paul.Hyperion;

import android.app.Activity;
import android.graphics.Color;
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.LinearLayout;
import android.widget.TextView;

public class FixtureItemAdapter extends BaseAdapter {

    private Activity context;
    public int size;
    private ImageView image;
    private TextView label;

    public FixtureItemAdapter(Activity context, int size) {
        super();
        this.context = context;
        this.size = size;
    }

    public int getCount() {
        // TODO Auto-generated method stub
        return size;
    }

    public Object getItem(int arg0) {
        // TODO Auto-generated method stub
        return null;
    }

    public long getItemId(int position) {
        // TODO Auto-generated method stub
        return 0;
    }



    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        // TODO Auto-generated method stub


        Log.v("Hyperion","convertView is Null?="+Boolean.toString(convertView==null));
        if (convertView == null) {
            LayoutInflater inflater = context.getLayoutInflater();
            convertView = (LinearLayout) inflater.inflate(net.blakely.paul.Hyperion.R.layout.outputitem, null, true);

            image = (ImageView) convertView.findViewById(net.blakely.paul.Hyperion.R.id.imageView1);
            Log.v("Hyperion","image is Null?="+Boolean.toString(image==null));
            label = (TextView) convertView.findViewById(net.blakely.paul.Hyperion.R.id.textView2);


        } 

        // Decide which channel this is and set information accordingly

        image.setBackgroundColor(Color.GREEN);
        label.setText("LABEL");

        return convertView;
    }

}

非常感谢您对此问题的任何帮助。物有所值。我发现当第一次运行适配器时我得到了NPE，当convertView为null时，图像也会变为空。

Answer 1

你打电话

image.setBackgroundColor(Color.GREEN);
label.setText("LABEL");

如果我们没有输入if语句图像并且没有实例化标签对象，那么当你调用setBackroundColr和setText时你会得到一个空指针异常：

@Override
    public View getView(int position, View convertView, ViewGroup parent) {
        // TODO Auto-generated method stub


        Log.v("Hyperion","convertView is Null?="+Boolean.toString(convertView==null));
        if (convertView == null) {
            LayoutInflater inflater = context.getLayoutInflater();
            convertView = (LinearLayout) inflater.inflate(net.blakely.paul.Hyperion.R.layout.outputitem, null, true);

        } 
          image = (ImageView)convertView.findViewById(net.blakely.paul.Hyperion.R.id.imageView1);
          label = (TextView) convertView.findViewById(net.blakely.paul.Hyperion.R.id.textView2);
        // Decide which channel this is and set information accordingly

        image.setBackgroundColor(Color.GREEN);
        label.setText("LABEL");

Answer 2

对不起，但我发现了我的问题。事实证明，我正在调用错误的xml文件，即outputitem而不是fixtureitem，因为我从程序中的另一个ListAdapter复制了该行。谢谢你的回答。

适用于Android的GridView自定义适配器

2 个答案: