我是开发 android 的新手。 在编写代码并运行调试器后,我得到了:“不幸的是,应用程序已停止”
我的 MainActivity.java
package instaroggie.nl.content;
import android.app.Activity;
import android.app.ActionBar;
import android.app.Fragment;
import android.os.Bundle;
import android.view.KeyEvent;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.os.Build;
import android.widget.ArrayAdapter;
import android.widget.EditText;
import android.widget.ListView;
import java.util.ArrayList;
import java.util.List;
public class MainActivity extends Activity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
ListView myListView = (ListView) findViewById(R.id.myListView);
final EditText myEditText = (EditText) findViewById(R.id.myEditText);
//create the Array List of to do items
final ArrayList<String> todoItems = new ArrayList<String>();
//create the Array Adapter to bind the array to the List View
final ArrayAdapter<String> aa;
aa = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, todoItems);
myListView.setAdapter(aa);
myEditText.setOnKeyListener(new View.OnKeyListener() {
public boolean onKey(View v, int keyCode, KeyEvent event) {
if (event.getAction() == KeyEvent.ACTION_DOWN)
if ((keyCode == KeyEvent.KEYCODE_DPAD_CENTER) ||
(keyCode == KeyEvent.KEYCODE_ENTER)) {
todoItems.add(0, myEditText.getText().toString());
aa.notifyDataSetChanged();
myEditText.setText("");
return true;
}
return false;
}
});
if (savedInstanceState == null) {
getFragmentManager().beginTransaction()
.add(R.id.container, new PlaceholderFragment())
.commit();
}
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
/**
* A placeholder fragment containing a simple view.
*/
public static class PlaceholderFragment extends Fragment {
public PlaceholderFragment() {
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_main, container, false);
return rootView;
}
}
我的 activity_main.xml:
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/container"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity"
tools:ignore="MergeRootFrame" />
和我的 fragment_main.xml:
<?xml version="1.0" encoding="utf-8" ?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent">
<EditText
android:id="@+id/myEditText"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:hint="@string/addItemHint"
android:contentDescription="@string/addItemContentDescription"/>
<ListView
android:id="@+id/myListView"
android:layout_width="match_parent"
android:layout_height="wrap_content" />
</LinearLayout>
有人知道我的问题出在哪里吗?
最佳答案
setContentView(R.layout.activity_main);
ListView myListView = (ListView) findViewById(R.id.myListView);
activity_main.xml
没有 id 为 myListView
的 ListView 。 findviewById
查找具有当前膨胀布局中提到的 id 的 View 。如果您的 activity_main.xml
没有 id 为 myListView
的 ListView ,并且您尝试在 Activity 中初始化 ListView,则会出现 NPE。
<ListView
android:id="@+id/myListView" // is in fragment_main.xml
尝试
FragmentTransaction fragTran = getSupportFragmentManager().beginTransaction();
fragTran.replace(R.id.containere, new PlaceholderFragment());
fragTran.commit();
膨胀 fragment_main.xml
并在 fragment 的 onCreateView
中初始化您的 View 。
ListView myListView;
EditText myEditText;
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_main, container, false);
myListView = (ListView) rootView.findViewById(R.id.myListView);
myEditText = (EditText) rootView.findViewById(R.id.myEditText);
...// rest of the code
return rootView;
}
关于android - 不幸的是 "App"已经停止了 Android Studio,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/20403927/