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尝试将输入文本保存到ArrayList并在可点击的ListView上显示ArrayList,应用程序不断崩溃

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所以我试图将输入(数字)保存到 ArrayList ,然后在可点击的 ListView 上显示 ArrayList .

当我试图启动应用程序时,它一直在崩溃,我哪里出错了?

public class MainActivity extends AppCompatActivity {
    EditText numberIn;
    ListView numberList;
    Button saveBtn;
    String numberToSave;
    ArrayList<String> allNumbers = new ArrayList<String>();

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        numberIn = (EditText) findViewById(R.id.editText);
        numberList = (ListView) findViewById(R.id.listView1);
        saveBtn = (Button) findViewById(R.id.button);

        myNumbers();

        final ArrayAdapter<String> arrayAdapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, allNumbers);

        numberList.setAdapter(arrayAdapter);
        numberList.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> parent, View view, int position, long id) {

                String selectedNumber = arrayAdapter.getItem(position);
            }
        });

        saveBtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                numberToSave = numberIn.getText().toString();
                myNumbers();
            }
        });
    }
    public void myNumbers(){
        allNumbers.add(numberToSave);
    }
}

logcat的: -

05-20 13:07:54.416 8449-8449/com.example.tsury.listex E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.tsury.listex, PID: 8449
java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String java.lang.Object.toString()' on a null object reference
    at android.widget.ArrayAdapter.createViewFromResource(ArrayAdapter.java:409)
    at android.widget.ArrayAdapter.getView(ArrayAdapter.java:371)
    at android.widget.AbsListView.obtainView(AbsListView.java:2363)
    at android.widget.ListView.makeAndAddView(ListView.java:1970)
    at android.widget.ListView.fillDown(ListView.java:704)
    at android.widget.ListView.fillFromTop(ListView.java:765)
    at android.widget.ListView.layoutChildren(ListView.java:1744)
    at android.widget.AbsListView.onLayout(AbsListView.java:2162)
    at android.view.View.layout(View.java:17637)
    at android.view.ViewGroup.layout(ViewGroup.java:5575)
    at android.support.constraint.ConstraintLayout.onLayout(ConstraintLayout.java:1197)
    at android.view.View.layout(View.java:17637)
    at android.view.ViewGroup.layout(ViewGroup.java:5575)
    at android.widget.FrameLayout.layoutChildren(FrameLayout.java:323)
    at android.widget.FrameLayout.onLayout(FrameLayout.java:261)
    at android.view.View.layout(View.java:17637)
    at android.view.ViewGroup.layout(ViewGroup.java:5575)
    at android.support.v7.widget.ActionBarOverlayLayout.onLayout(ActionBarOverlayLayout.java:437)
    at android.view.View.layout(View.java:17637)
    at android.view.ViewGroup.layout(ViewGroup.java:5575)
    at android.widget.FrameLayout.layoutChildren(FrameLayout.java:323)
    at android.widget.FrameLayout.onLayout(FrameLayout.java:261)
    at android.view.View.layout(View.java:17637)
    at android.view.ViewGroup.layout(ViewGroup.java:5575)
    at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1741)
    at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1585)
    at android.widget.LinearLayout.onLayout(LinearLayout.java:1494)
    at android.view.View.layout(View.java:17637)
    at android.view.ViewGroup.layout(ViewGroup.java:5575)
    at android.widget.FrameLayout.layoutChildren(FrameLayout.java:323)
    at android.widget.FrameLayout.onLayout(FrameLayout.java:261)
    at com.android.internal.policy.DecorView.onLayout(DecorView.java:726)
    at android.view.View.layout(View.java:17637)
    at android.view.ViewGroup.layout(ViewGroup.java:5575)
    at android.view.ViewRootImpl.performLayout(ViewRootImpl.java:2346)
    at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:2068)
    at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1254)
    at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:6337)
    at android.view.Choreographer$CallbackRecord.run(Choreographer.java:874)
    at android.view.Choreographer.doCallbacks(Choreographer.java:686)
    at android.view.Choreographer.doFrame(Choreographer.java:621)
    at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:860)
    at android.os.Handler.handleCallback(Handler.java:751)
    at android.os.Handler.dispatchMessage(Handler.java:95)
    at android.os.Looper.loop(Looper.java:154)
    at android.app.ActivityThread.main(ActivityThread.java:6119)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)

3 回答

  • 0

    您希望在扩充布局之前获取TextView,因此它是一个简单的NullPointerExecption . 更改您的代码:

    公共类ListViewDemo扩展ListActivity {

    ArrayList<String> listItems=new ArrayList<String>();
    ArrayAdapter<String> adapter;
    
    TextView theFact;
    String shareFact;
    
    
    @Override
    public void onCreate(Bundle icicle) {
        super.onCreate(icicle);
        setContentView(R.layout.main);
    
        theFact = (TextView) findViewById(R.id.tvContent)
        shareFact = theFact.getText().toString();
    
        adapter=new ArrayAdapter<String>(this,
        android.R.layout.simple_list_item_1,
        listItems);
        setListAdapter(adapter);
    
        listItems.add(shareFact);
        adapter.notifyDataSetChanged();
    }
    

    如果按下按钮,它将调用addItems()函数(如您设置的那样),但它尚未实现,因此它将生成其他错误 .

    public void addItems(View v) {
        listItems.add(shareFact);
        adapter.notifyDataSetChanged();
    }
    

    onCreate() 方法下添加此函数,并将 listItems.add()adapter.notifyDataSetChanged() 行移动到此新方法 .

  • 0

    尝试

    saveBtn.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            if(numberIn.getText() != null){
                numberToSave = numberIn.getText().toString();
                myNumbers();
            }
        }
    });
    
  • 0

    您尝试在此处对空对象调用 .toString()

    numberToSave = numberIn.getText().toString();

    您可能希望先添加一个空检查:

    saveBtn.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            if (numberIn.getText() != null {
                numberToSave = numberIn.getText().toString();
                myNumbers();
            }
        }
    });
    

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