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我试图制作一个提醒笔记的 ListView。但是当我尝试保存它并将其显示在 ListView 中时，应用程序会因此错误/异常而崩溃。saveNote当你按下保存按钮时调用方法。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();
        }
    });

日志猫

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)
4

3 回答 3

1

我从日志中发现的主要原因是 ListView 为空。如果 listView 为空，请再检查一次？还有什么是notes[i] = note ？？我认为在每个 Save 按钮单击中，您每次都会找到 ListView 和设置 Adapter。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，下一次只需更新适配器数据并调用 notifyDataSetChanged();

于 2015-09-15T07:06:41.513 回答
0

调试并找出为什么在您的布局中找不到您的 ListView（为空）。

于 2015-09-15T06:57:33.810 回答
0

问题在于以下行：

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

请检查您的 xml 是否有 ID 为的 ListView 小部件'list'。如果 id 在 XML 中不同，它将导致 NULL 对象引用。你打电话时

listView.setAdapter(adapter)

它将给出一个 NULL 指针异常。

于 2015-09-15T07:03:18.420 回答