Question

我有一个userinfo列表，其中包含每个列表行中的名称，地址和按钮。单击一行中的按钮，它应导航到另一个活动。没有错误。但是app崩溃了。在onclick中打印值（名称和地址）没有问题。问题仅在于开始活动。

public View getView(final int position, View convertView, ViewGroup parent) {

    ViewHolder holder = null;
    LayoutInflater inflater = (LayoutInflater) activity
            .getSystemService(Activity.LAYOUT_INFLATER_SERVICE);

    if (convertView == null) {

        convertView = inflater.inflate(R.layout.list_friends, parent, false);
        holder = new ViewHolder(convertView);
        convertView.setTag(holder);
    } else {

        holder = (ViewHolder) convertView.getTag(); 
    }
    final Userinfo userinf = userinf.get(position);
    holder.button = (Button) convertView.findViewById(R.id.button);
    holder.button.setTag(position);
    holder.button.setOnClickListener(new View.OnClickListener() {
    public void onClick(View v) {

            System.out.println(position);
            System.out.println(userinf.getName());
            System.out.println(userinf.getAddress());

            Intent i=new Intent(mContext,Details.class);
            mContext.startActivity(i);
        }
    });

    return convertView;
}

错误日志：

    E/AndroidRuntime: FATAL EXCEPTION: main
              Process: com.example.user, PID: 13057
              java.lang.NullPointerException: Attempt to invoke virtual      method 'java.lang.String android.content.Context.getPackageName()' on a null object reference
                  at android.content.ComponentName.<init>(ComponentName.java:128)
                  at android.content.Intent.<init>(Intent.java:5328)
                  at com.example.appko.user.Listviewadapter$1.onClick(Listviewadapter.java:84)
                  at android.view.View.performClick(View.java:5721)
                  at android.widget.TextView.performClick(TextView.java:10931)
                  at android.view.View$PerformClick.run(View.java:22620)
                  at android.os.Handler.handleCallback(Handler.java:739)
                  at android.os.Handler.dispatchMessage(Handler.java:95)
                  at android.os.Looper.loop(Looper.java:148)
                  at android.app.ActivityThread.main(ActivityThread.java:7409)
                  at java.lang.reflect.Method.invoke(Native Method)
                  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230)
                  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120)

Listview适配器第84行是

     Intent i=new Intent(mContext,Details.class);

Details.class只是一个在Textview中打印Hi的测试类

Answer 1

试试这个

 Intent i=new Intent(activity,Details.class);
        activity.startActivity(i);

Answer 2

您可能必须包含

intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);

如果您可以附加日志，则更容易识别

使用Viewholder在listview中使用onclick按钮启动活动

2 个答案: