如何在lazyadapter->getItem() 中设置onclicklistener 并在onClick 方法中启动活动

Question

我在列表视图中有两个“编辑”和“删除”按钮，当用户单击一个按钮时，我必须为编辑和删除按钮启动一个新活动“EditActivity 或 DeleteActivity”。

`public 类 DepartmentAdapter 扩展 ArrayAdapter 实现 OnClickListener {

int resource;
String response;
Context context;
//Initialize adapter
public DepartmentAdapter(Context _context, int resource, ArrayList<Department> items) {
    super(_context, resource, items);
    this.resource=resource;

    context = _context;
}


@Override
public View getView(int position, View convertView, ViewGroup parent)
{
        LinearLayout deptView;
    //Get the current Department  object
    Department dept = getItem(position);

    //Inflate the view
    if(convertView==null)
    {
        deptView = new LinearLayout(getContext());
        String inflater = Context.LAYOUT_INFLATER_SERVICE;
        LayoutInflater vi;
        vi = (LayoutInflater)getContext().getSystemService(inflater);
        vi.inflate(resource, deptView, true);
    }
    else
    {
        deptView = (LinearLayout) convertView;
    }
    //Get the text boxes from the listitem.xml file
    TextView id =(TextView)deptView.findViewById(R.id.Id);
    TextView sname =(TextView)deptView.findViewById(R.id.sname);
    TextView name =(TextView)deptView.findViewById(R.id.name); 
    //Assign the appropriate data from our Department object above
    id.setText(Integer.toString(dept.getID()));
    sname.setText(dept.getDepartmentShortName());
    name.setText(dept.getDepartmentName());

    Button edit = (Button)deptView.findViewById(R.id.edit);
    //del= (Button)deptListView.findViewById(R.id.del);
    ShowDepertment  d = new ShowDepertment();       

    edit.setOnClickListener(this);


}

public void onClick(View v) {

    Intent myIntent = new Intent(context , AddDepertment.class);
    myIntent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
    context.startActivity(myIntent);        
}

}`

在 onclick() 中，无法启动活动并出现错误：

10-21 13:15:11.116: E/AndroidRuntime(11718): FATAL EXCEPTION: main 10-21 13:15:11.116: E/AndroidRuntime(11718): java.lang.NullPointerException 10-21 13:15:11.116: E/AndroidRuntime(11718): at my.mewappattendance.myAdapters.DepartmentAdapter.getView(DepartmentAdapter.java:80) 10-21 13:15:11.116: E/AndroidRuntime(11718): at android.widget.AbsListView.obtainView(AbsListView.java:2033) 10-21 13:15:11.116: E/AndroidRuntime(11718): at android.widget.ListView.measureHeightOfChildren(ListView.java:1244) 10-21 13:15:11.116: E/AndroidRuntime(11718): at android.widget.ListView.onMeasure(ListView.java:1155) 10-21 13:15:11.116: E/AndroidRuntime(11718): at android.view.View.measure(View.java:12727) 10-21 13:15:11.116: E/AndroidRuntime(11718): at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4698) 10-21 13:15:11.116: E/AndroidRuntime(11718): at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1369) 10-21 13:15:11.116: E/AndroidRuntime(11718): at android.widget.LinearLayout.measureVertical(LinearLayout.java:660) 10-21 13:15:11.116: E/AndroidRuntime(11718): at android.widget.LinearLayout.onMeasure(LinearLayout.java:553) 10-21 13:15:11.116: E/AndroidRuntime(11718): at android.view.View.measure(View.java:12727) 10-21 13:15:11.116: E/AndroidRuntime(11718): at android.widget.LinearLayout.measureHorizontal(LinearLayout.java:1196) 10-21 13:15:11.116: E/AndroidRuntime(11718): at android.widget.LinearLayout.onMeasure(LinearLayout.java:555) 10-21 13:15:11.116: E/AndroidRuntime(11718): at android.view.View.measure(View.java:12727) 10-21 13:15:11.116: E/AndroidRuntime(11718): at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4698) 10-21 13:15:11.116: E/AndroidRuntime(11718): at android.widget.FrameLayout.onMeasure(FrameLayout.java:293) 10-21 13:15:11.116: E/AndroidRuntime(11718): at android.view.View.measure(View.java:12727) 10-21 13:15:11.116: E/AndroidRuntime(11718): at android.widget.LinearLayout.measureVertical(LinearLayout.java:812) 10-21 13:15:11.116: E/AndroidRuntime(11718): at android.widget.LinearLayout.onMeasure(LinearLayout.java:553) 10-21 13:15:11.116: E/AndroidRuntime(11718): at android.view.View.measure(View.java:12727) 10-21 13:15:11.116: E/AndroidRuntime(11718): at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4698) 10-21 13:15:11.116: E/AndroidRuntime(11718): at android.widget.FrameLayout.onMeasure(FrameLayout.java:293) 10-21 13:15:11.116: E/AndroidRuntime(11718): at com.android.internal.policy.impl.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2092) 10-21 13:15:11.116: E/AndroidRuntime(11718): at android.view.View.measure(View.java:12727) 10-21 13:15:11.116: E/AndroidRuntime(11718): at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1068) 10-21 13:15:11.116: E/AndroidRuntime(11718): at android.view.ViewRootImpl.handleMessage(ViewRootImpl.java:2446) 10-21 13:15:11.116: E/AndroidRuntime(11718): at android.os.Handler.dispatchMessage(Handler.java:99) 10-21 13:15:11.116: E/AndroidRuntime(11718): at android.os.Looper.loop(Looper.java:137) 10-21 13:15:11.116: E/AndroidRuntime(11718): at android.app.ActivityThread.main(ActivityThread.java:4424) 10-21 13:15:11.116: E/AndroidRuntime(11718): at java.lang.reflect.Method.invokeNative(Native Method) 10-21 13:15:11.116: E/AndroidRuntime(11718): at java.lang.reflect.Method.invoke(Method.java:511) 10-21 13:15:11.116: E/AndroidRuntime(11718): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784) 10-21 13:15:11.116: E/AndroidRuntime(11718): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551) 10-21 13:15:11.116: E/AndroidRuntime(11718): at dalvik.system.NativeStart.main(Native Method)

Answer 1

发生这种情况是因为当您单击按钮时，GC 会从内存中删除 Adapter 类，因此您必须通过以下方式向按钮添加侦听器：

button.setOnClickListener(new OnClickListener(){

@Override
public void onClick(View v) {
}
});