Question

我正在尝试制作提醒备注的ListView。但是，当我尝试保存并在ListView中显示它时，应用程序崩溃时出现此错误/异常。按保存按钮时会调用saveNote方法。任何帮助表示赞赏。

    public boolean onOptionsItemSelected(MenuItem item) {

    int id = item.getItemId();
    switch(id) {
      case R.id.add_reminder : {
          et = (EditText)findViewById(R.id.new_note);
          et.setVisibility(View.VISIBLE);
          note = et.getText().toString();
          i++;
          Button save_button = (Button) findViewById(R.id.button_save);
          save_button.setVisibility(View.VISIBLE);
      }
      default : return super.onOptionsItemSelected(item);
  }

}
public void saveNote(View view) {

    String[] notes = new String[20];
    notes[i] = note;
    listView = (ListView) findViewById(R.id.list);
    ArrayAdapter<String> adapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, android.R.id.text1,notes);
    listView.setAdapter(adapter);
    listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {

        @Override
        public void onItemClick(AdapterView<?> parent, View view, int position, long id) {

            //Clicked item index
            int itemPosition = position;
            //Clicked item value
            String itemNote = (String) listView.getItemAtPosition(position);
            //Alert
            Toast.makeText(getApplicationContext(), "Position :" + itemPosition + "  ListItem : " + itemNote, Toast.LENGTH_LONG).show();
        }
    });

logcat的

java.lang.IllegalStateException: Could not execute method of the activity
            at android.view.View$1.onClick(View.java:4020)
            at android.view.View.performClick(View.java:4780)
            at android.view.View$PerformClick.run(View.java:19866)
            at android.os.Handler.handleCallback(Handler.java:739)
            at android.os.Handler.dispatchMessage(Handler.java:95)
            at android.os.Looper.loop(Looper.java:135)
            at android.app.ActivityThread.main(ActivityThread.java:5257)
            at java.lang.reflect.Method.invoke(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:372)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)
     Caused by: java.lang.reflect.InvocationTargetException
            at java.lang.reflect.Method.invoke(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:372)
            at android.view.View$1.onClick(View.java:4015)
            at android.view.View.performClick(View.java:4780)
            at android.view.View$PerformClick.run(View.java:19866)
            at android.os.Handler.handleCallback(Handler.java:739)
            at android.os.Handler.dispatchMessage(Handler.java:95)
            at android.os.Looper.loop(Looper.java:135)
            at android.app.ActivityThread.main(ActivityThread.java:5257)
            at java.lang.reflect.Method.invoke(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:372)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)
     Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ListView.setAdapter(android.widget.ListAdapter)' on a null object reference
            at com.cokosofts.pramith.reminder.MainActivity.saveNote(MainActivity.java:69)
            at java.lang.reflect.Method.invoke(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:372)
            at android.view.View$1.onClick(View.java:4015)
            at android.view.View.performClick(View.java:4780)
            at android.view.View$PerformClick.run(View.java:19866)
            at android.os.Handler.handleCallback(Handler.java:739)
            at android.os.Handler.dispatchMessage(Handler.java:95)
            at android.os.Looper.loop(Looper.java:135)
            at android.app.ActivityThread.main(ActivityThread.java:5257)
            at java.lang.reflect.Method.invoke(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:372)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)

Answer 1

我在Logs中找到的主要原因是ListView为null。如果listView为空，请再次检查？还有什么是notes[i] = note ?? 我想在每个保存按钮单击您每次都找到ListView和设置适配器。从我的角度来看，这不是一个好方法。您应该第一次设置适配器，下次只需更新适配器数据并调用notifyDataSetChanged（）;

Answer 2

调试并找出在布局中找不到ListView的原因（为空）。

Answer 3

问题在于以下几行：

listView = (ListView) findViewById(R.id.list);

请检查您的xml是否包含ID为'list'的ListView小部件。如果XML在XML中不同，则会导致NULL对象引用。当你打电话

listView.setAdapter(adapter)

它将给出一个NULL指针异常。

显示ListView时获取NullPointerException

3 个答案: