[英]Android Developing App crashes on startup
我目前正在开发一个包含自定义ListView
的应用程序。 我开发了一个自定义阵列适配器。 我认为我的应用程序在此处崩溃:
ListView DirectoryView = (ListView) findViewById(R.id.fileListView);
所以我认为错误是在activity_main.xml中:
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="fill_parent"
android:layout_height="fill_parent" >
<ListView
android:id="@+id/fileListView"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:layout_weight="1" >
</ListView>
这是我的LogCat:
09-09 11:19:21.254: E/Trace(1152): error opening trace file: No such file or directory (2)
09-09 11:19:21.484: D/AndroidRuntime(1152): Shutting down VM
09-09 11:19:21.484: W/dalvikvm(1152): threadid=1: thread exiting with uncaught exception (group=0x40a13300)
09-09 11:19:21.504: E/AndroidRuntime(1152): FATAL EXCEPTION: main
09-09 11:19:21.504: E/AndroidRuntime(1152): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.teamdroid.explorer/com.teamdroid.explorer.MainActivity}: java.lang.NullPointerException
09-09 11:19:21.504: E/AndroidRuntime(1152): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2059)
09-09 11:19:21.504: E/AndroidRuntime(1152): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2084)
09-09 11:19:21.504: E/AndroidRuntime(1152): at android.app.ActivityThread.access$600(ActivityThread.java:130)
09-09 11:19:21.504: E/AndroidRuntime(1152): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195)
09-09 11:19:21.504: E/AndroidRuntime(1152): at android.os.Handler.dispatchMessage(Handler.java:99)
09-09 11:19:21.504: E/AndroidRuntime(1152): at android.os.Looper.loop(Looper.java:137)
09-09 11:19:21.504: E/AndroidRuntime(1152): at android.app.ActivityThread.main(ActivityThread.java:4745)
09-09 11:19:21.504: E/AndroidRuntime(1152): at java.lang.reflect.Method.invokeNative(Native Method)
09-09 11:19:21.504: E/AndroidRuntime(1152): at java.lang.reflect.Method.invoke(Method.java:511)
09-09 11:19:21.504: E/AndroidRuntime(1152): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
09-09 11:19:21.504: E/AndroidRuntime(1152): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
09-09 11:19:21.504: E/AndroidRuntime(1152): at dalvik.system.NativeStart.main(Native Method)
09-09 11:19:21.504: E/AndroidRuntime(1152): Caused by: java.lang.NullPointerException
09-09 11:19:21.504: E/AndroidRuntime(1152): at android.app.Activity.findViewById(Activity.java:1825)
09-09 11:19:21.504: E/AndroidRuntime(1152): at com.teamdroid.explorer.listDirectory.getDirectory(listDirectory.java:20)
09-09 11:19:21.504: E/AndroidRuntime(1152): at com.teamdroid.explorer.MainActivity.onCreate(MainActivity.java:33)
09-09 11:19:21.504: E/AndroidRuntime(1152): at android.app.Activity.performCreate(Activity.java:5008)
09-09 11:19:21.504: E/AndroidRuntime(1152): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1079)
09-09 11:19:21.504: E/AndroidRuntime(1152): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2023)
09-09 11:19:21.504: E/AndroidRuntime(1152): ... 11 more
请你帮我一下。 我正在搜索此错误2天。 谢谢!
编辑:我有第三个文件,它在此listview
列出目录:
public class listDirectory extends ListActivity {
String[] DirList;
public void onCreate(Bundle icicle) {
setContentView(R.layout.activity_main);
super.onCreate(icicle);
}
public void getDirectory (){
MainActivity main = new MainActivity();
String path = main.getPath();
ListView DirectoryView = (ListView) findViewById(R.id.fileListView);
CustomArrayAdapter adapter = new CustomArrayAdapter(getApplicationContext(), DirList);
File file = new File(path);
File[] FileList = file.listFiles();
java.util.Arrays.sort(FileList);
for(int i = 0; i < FileList.length; i++){
if(FileList[i].isDirectory()){
DirList[i] = (FileList[i].getName() + " [folder]");
} else{
DirList[i] = (FileList[i].getName() + " [file]");
}
}
DirectoryView.setAdapter(adapter);
}
}
我认为在此文件中是错误。
我认为您没有在onCreate()方法中设置内容视图,因此findViewById无法找到视图对象,因此返回null。
假设您的XML布局文件是my_layout.xml。 在onCreate(...)内部添加以下行:
setContentView(R.layout.my_layout);
非常混乱的代码...
我认为在您的MainActivity
您新建了listDirectory
的实例,但不会调用listDirectory.onCreate()
,因此内容视图为null。 因此listDirectory.getDirectory()
findViewById()
内的findViewById()
在listDirectory的内容视图中查找的视图不是MainActivity的,而这是null并导致NPE
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