每当我运行我的SetList方法时,在启动时创建应用程序崩溃(通过点击事件等方式调用该方法时工作正常) 我对android开发很新,所以我不完全确定程序启动的操作顺序。 第130行:lv.setAdapter(适配器);
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
if (savedInstanceState == null) {
getFragmentManager().beginTransaction()
.add(R.id.container, new PlaceholderFragment())
.commit();
}
LoadLogs();
}
ArrayList<String> Logs = new ArrayList<String>();
String path = Environment.getExternalStorageDirectory().getAbsolutePath();
String name = "Logs.txt";
boolean Returned = true;
public void LoadLogs()
{
File file = new File(path,name);
try
{
if(!file.exists())
{
file.createNewFile();
}
}
catch(Exception e)
{
e.printStackTrace();
}
try {
BufferedReader bufferedReader = new BufferedReader(new FileReader(file));
String l;
Returned = true;
while (( l = bufferedReader.readLine()) != null) {
Returned = l.contains("Returned");
Logs.add(l);
}
} catch (Exception e) {
e.printStackTrace();
}
SetList();
}
public void SetList()
{
ListView lv = (ListView) findViewById(R.id.listView1);
ArrayAdapter<String> adapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1,Logs);
lv.setAdapter(adapter);
}
布局:
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context=".MainActivity$PlaceholderFragment" >
<Button
android:id="@+id/button2"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_above="@+id/button1"
android:layout_centerHorizontal="true"
android:onClick="onClickLog"
android:text="Log" />
<Button
android:id="@+id/button1"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_alignLeft="@+id/button2"
android:layout_alignParentBottom="true"
android:onClick="onClickEmail"
android:text="Email" />
<ListView
android:id="@+id/listView1"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_above="@+id/button2"
android:layout_alignParentTop="true"
android:layout_centerHorizontal="true" >
</ListView>
logcat的
05-12 13:22:49.795: D/AndroidRuntime(2122): Shutting down VM
05-12 13:22:49.795: W/dalvikvm(2122): threadid=1: thread exiting with uncaught exception (group=0xb2ababa8)
05-12 13:22:49.825: E/AndroidRuntime(2122): FATAL EXCEPTION: main
05-12 13:22:49.825: E/AndroidRuntime(2122): Process: com.example.gs4depositalogging, PID: 2122
05-12 13:22:49.825: E/AndroidRuntime(2122): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.gs4depositalogging/com.example.gs4depositalogging.MainActivity}: java.lang.NullPointerException
05-12 13:22:49.825: E/AndroidRuntime(2122): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2195)
05-12 13:22:49.825: E/AndroidRuntime(2122): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
05-12 13:22:49.825: E/AndroidRuntime(2122): at android.app.ActivityThread.access$800(ActivityThread.java:135)
05-12 13:22:49.825: E/AndroidRuntime(2122): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
05-12 13:22:49.825: E/AndroidRuntime(2122): at android.os.Handler.dispatchMessage(Handler.java:102)
05-12 13:22:49.825: E/AndroidRuntime(2122): at android.os.Looper.loop(Looper.java:136)
05-12 13:22:49.825: E/AndroidRuntime(2122): at android.app.ActivityThread.main(ActivityThread.java:5017)
05-12 13:22:49.825: E/AndroidRuntime(2122): at java.lang.reflect.Method.invokeNative(Native Method)
05-12 13:22:49.825: E/AndroidRuntime(2122): at java.lang.reflect.Method.invoke(Method.java:515)
05-12 13:22:49.825: E/AndroidRuntime(2122): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
05-12 13:22:49.825: E/AndroidRuntime(2122): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
05-12 13:22:49.825: E/AndroidRuntime(2122): at dalvik.system.NativeStart.main(Native Method)
05-12 13:22:49.825: E/AndroidRuntime(2122): Caused by: java.lang.NullPointerException
05-12 13:22:49.825: E/AndroidRuntime(2122): at com.example.gs4depositalogging.MainActivity.SetList(MainActivity.java:130)
05-12 13:22:49.825: E/AndroidRuntime(2122): at com.example.gs4depositalogging.MainActivity.LoadLogs(MainActivity.java:124)
05-12 13:22:49.825: E/AndroidRuntime(2122): at com.example.gs4depositalogging.MainActivity.onCreate(MainActivity.java:41)
05-12 13:22:49.825: E/AndroidRuntime(2122): at android.app.Activity.performCreate(Activity.java:5231)
05-12 13:22:49.825: E/AndroidRuntime(2122): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
05-12 13:22:49.825: E/AndroidRuntime(2122): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2159)
05-12 13:22:49.825: E/AndroidRuntime(2122): ... 11 more
答案 0 :(得分:0)
您的ListView
位于PlaceholderFragment
布局中,而不在活动布局中。您无法使用findViewById()
从onCreate()
调用的方法检索它。尝试在空列表视图上调用setListAdapter()
是NPE的直接原因。
设置片段视图的最佳位置和时间是片段onCreateView()
。
还考虑在后台线程上进行文件I / O,例如使用AsyncTask
。