Question

我是android studio的新手，并不知道我在做什么。我正在尝试将项目添加到列表视图中，但当我尝试转到第二页时，应用程序崩溃了。（该应用有两页，当第二页“空”时没有发生崩溃。）

以下是我的XML。

<ListView
    android:id="@+id/list1"
    android:layout_width="368dp"
    android:layout_height="373dp"
    android:layout_marginBottom="8dp"
    android:layout_marginEnd="8dp"
    android:layout_marginLeft="8dp"
    android:layout_marginRight="8dp"
    android:layout_marginStart="8dp"
    android:layout_marginTop="8dp"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintHorizontal_bias="0.0"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toTopOf="parent"
    app:layout_constraintVertical_bias="1.0" />

<EditText
    android:id="@+id/laggtill"
    android:layout_width="340dp"
    android:layout_height="54dp"
    android:layout_marginBottom="8dp"
    android:layout_marginEnd="8dp"
    android:layout_marginLeft="8dp"
    android:layout_marginRight="8dp"
    android:layout_marginStart="8dp"
    android:layout_marginTop="8dp"
    android:hint="@string/Sida2Hint"
    app:layout_constraintBottom_toTopOf="@+id/list1"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toTopOf="parent"
    app:layout_constraintVertical_bias="0.133" />

<Button
    android:id="@+id/addButton"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_marginBottom="8dp"
    android:layout_marginEnd="8dp"
    android:layout_marginLeft="8dp"
    android:layout_marginRight="8dp"
    android:layout_marginStart="8dp"
    android:layout_marginTop="8dp"
    android:text="@string/Sida2Add"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintHorizontal_bias="0.942"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toTopOf="parent"
    app:layout_constraintVertical_bias="0.143" />

以下是我的java课程。

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ListView;

import java.util.ArrayList;

public class sida2 extends AppCompatActivity {

    private Button btnAdd;
    private EditText et;
    private ListView lv;

    ArrayList<String> Uppgifter = new ArrayList<String>();
    ArrayAdapter<String> adapter;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_sida2);

        btnAdd = (Button) findViewById(R.id.addButton);
        btnAdd.setOnClickListener((View.OnClickListener) this);
        et = (EditText) findViewById(R.id.laggtill);
        adapter = new ArrayAdapter<String>(this, android.R.layout.simple_expandable_list_item_1, R.id.list1);

        lv = (ListView) findViewById(R.id.list1);
        lv.setAdapter(adapter);
    }

    public void onClick(View v) {
        String input = et.getText().toString();
        if (input.length() > 0) {
            // add string to the adapter, not the listview
            adapter.add(input);
            // no need to call adapter.notifyDataSetChanged(); as it is done by the adapter.add() method
        }
    }
}

当我尝试进入“第二页”时，应用程序崩溃了。我在工作室没有错误，我真的不知道该怎么做。感谢任何帮助！

Answer 1

public class sida2 extends AppCompatActivity实现了View.OnClickListener {

    private Button btnAdd;
    private EditText et;
    private ListView lv;

    ArrayList<String> Uppgifter = new ArrayList<String>();
    ArrayAdapter<String> adapter;

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

        btnAdd = (Button) findViewById(R.id.addButton);
        btnAdd.setOnClickListener(this);
        et = (EditText) findViewById(R.id.laggtill);
        adapter = new ArrayAdapter<String>(this, android.R.layout.simple_expandable_list_item_1, Uppgifter);

        lv = (ListView) findViewById(R.id.list1);
        lv.setAdapter(adapter);
    }

    @Override
    public void onClick(View view) {
        String input = et.getText().toString();
        if (input.length() > 0) {
            // add string to the adapter, not the listview
            Uppgifter.add(input);
            adapter.notifyDataSetChanged();

            // no need to call adapter.notifyDataSetChanged(); as it is done by the adapter.add() method
        }

    }
}

// XML

[![<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    >

    <ListView
        android:id="@+id/list1"
        android:layout_width="368dp"
        android:layout_height="373dp"
        android:layout_marginBottom="8dp"
        android:layout_marginEnd="8dp"
        android:layout_marginLeft="8dp"
        android:layout_marginRight="8dp"
        android:layout_marginStart="8dp"
        android:layout_marginTop="8dp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.0"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="1.0" />

    <EditText
        android:id="@+id/laggtill"
        android:layout_width="340dp"
        android:layout_height="54dp"
        android:layout_marginBottom="8dp"
        android:layout_marginEnd="8dp"
        android:layout_marginLeft="8dp"
        android:layout_marginRight="8dp"
        android:layout_marginStart="8dp"
        android:layout_marginTop="8dp"
        android:hint="aaaa"
        app:layout_constraintBottom_toTopOf="@+id/list1"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.133" />

    <Button
        android:id="@+id/addButton"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginBottom="8dp"
        android:layout_marginEnd="8dp"
        android:layout_marginLeft="8dp"
        android:layout_marginRight="8dp"
        android:layout_marginStart="8dp"
        android:layout_marginTop="8dp"
        android:text="aaa"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.942"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.143" />

</LinearLayout>][1]][1]

PS：尝试调试你的应用程序..你会学到很多东西。：）

在buttonclick上添加用户输入

1 个答案: