我最近在我的 Android 应用程序中添加了一个启动屏幕来屏蔽 JSON 文件的加载，但是我的应用程序在完成解析后崩溃了。在找到有问题的部分之前，我已经注释掉并取消注释掉了代码，但我不确定它为什么不起作用。
如果我从此代码段中注释掉 for 循环，则该代码有效。
来自 MagazinePagesActivity.java：
public void loadItems() {
for (Item item : SplashActivity.downloadedItems) {
Post post = (Post) item;
for (String tag : post.tags) {
if (tag.equals(this.tag)) {
// loader.loadImage(magazine.imageURL, new
// SimpleImageLoadingListener());
Bundle bundle = new Bundle();
bundle.putString("title", post.title);
bundle.putString("article", post.article);
bundle.putString("imageURL", post.imageURL);
MagazineFragment cover = new MagazineFragment();
cover.setArguments(bundle);
coverAdapter.addNewItem(cover);
}
}
}
setContentView(vp);
}
起初，我以为是因为 SplashActivity.downloadedItems 没有正确定义，但对我来说看起来不错：
来自 SplashActivity.java：
public static ArrayList<Item> downloadedItems = new ArrayList<Item>();
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_splash);
new RetreiveJSONTask() {
protected void onPostExecute(String JSON)
{
Log.d("SplashActivity", "Beginning parsingJSON" );
downloadedItems = parseJSON ( JSON );
Log.d("SplashActivity", "Finished parsingJSON" );
Log.d("SplashActivity", "" + SplashActivity.downloadedItems.isEmpty());
Intent i = new Intent(SplashActivity.this, MagazinePagesActivity.class);
startActivity(i);
// Closes the splash screen
finish();
}
}.execute(sourceURL());
}
来自 LogCat：
10-16 19:23:12.602: D/AndroidRuntime(828): Shutting down VM
10-16 19:23:12.602: W/dalvikvm(828): threadid=1: thread exiting with uncaught exception (group=0x41465700)
10-16 19:23:12.632: E/AndroidRuntime(828): FATAL EXCEPTION: main
10-16 19:23:12.632: E/AndroidRuntime(828): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.bruinfootball/com.dailybruin.bruinframework.channels.StoryListActivity}: java.lang.NullPointerException
10-16 19:23:12.632: E/AndroidRuntime(828): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2211)
10-16 19:23:12.632: E/AndroidRuntime(828): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2261)
10-16 19:23:12.632: E/AndroidRuntime(828): at android.app.ActivityThread.access$600(ActivityThread.java:141)
10-16 19:23:12.632: E/AndroidRuntime(828): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1256)
10-16 19:23:12.632: E/AndroidRuntime(828): at android.os.Handler.dispatchMessage(Handler.java:99)
10-16 19:23:12.632: E/AndroidRuntime(828): at android.os.Looper.loop(Looper.java:137)
10-16 19:23:12.632: E/AndroidRuntime(828): at android.app.ActivityThread.main(ActivityThread.java:5103)
10-16 19:23:12.632: E/AndroidRuntime(828): at java.lang.reflect.Method.invokeNative(Native Method)
10-16 19:23:12.632: E/AndroidRuntime(828): at java.lang.reflect.Method.invoke(Method.java:525)
10-16 19:23:12.632: E/AndroidRuntime(828): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
10-16 19:23:12.632: E/AndroidRuntime(828): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
10-16 19:23:12.632: E/AndroidRuntime(828): at dalvik.system.NativeStart.main(Native Method)
10-16 19:23:12.632: E/AndroidRuntime(828): Caused by: java.lang.NullPointerException
10-16 19:23:12.632: E/AndroidRuntime(828): at com.dailybruin.bruinframework.channels.StoryListActivity.loadItems(StoryListActivity.java:27)
10-16 19:23:12.632: E/AndroidRuntime(828): at com.dailybruin.bruinframework.channels.JSONItemsActivity.onCreate(JSONItemsActivity.java:20)
10-16 19:23:12.632: E/AndroidRuntime(828): at com.dailybruin.bruinframework.channels.StoryItemsActivity.onCreate(StoryItemsActivity.java:18)
10-16 19:23:12.632: E/AndroidRuntime(828): at com.dailybruin.bruinframework.channels.StoryListActivity.onCreate(StoryListActivity.java:18)
10-16 19:23:12.632: E/AndroidRuntime(828): at android.app.Activity.performCreate(Activity.java:5133)
10-16 19:23:12.632: E/AndroidRuntime(828): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
10-16 19:23:12.632: E/AndroidRuntime(828): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2175)
10-16 19:23:12.632: E/AndroidRuntime(828): ... 11 more
不确定它是否有帮助，但 SplashActivity 和 MagazinePagesActivity 都分别扩展了 JSONItemsActivity。
提前感谢您的帮助！我对Android相当陌生，所以请多多包涵。
编辑：这很奇怪，我用来检查 ArrayList 是否为空的调试语句返回 true，但是 parseJSON 中的另一个调试语句显示正在添加东西。我的 parseJSON 方法：
public ArrayList<Item> parseJSON(String jsonString) {
ArrayList<Item> magazines = new ArrayList<Item>();
JSONArray jArray;
try {
jArray = new JSONArray(jsonString);
JSONObject jObject;
JSONObject image;
String img;
String title;
String subtitle;
int commentCount;
String content;
String date;
String ID;
String slug;
JSONArray array;
String[] tags;
for (int i = 0; i < jArray.length(); i++) {
jObject = jArray.getJSONObject(i);
img = jObject.getString("tall_image_url");
if (img.equals(""))
img = jObject.getString("image_url");
if (img.equals("") && !jObject.isNull("poster_image")) {
image = jObject.getJSONObject("poster_image");
img = image.getString("name");
}
title = jObject.getString("title");
subtitle = jObject.getString("subtitle");
commentCount = jObject.getInt("comment_count");
content = jObject.getString("content_html");
date = jObject.getString("creation_date");
ID = jObject.getString("id");
slug = jObject.getString("slug");
array = jObject.getJSONArray("tags_list");
tags = new String[array.length()];
for (int j = 0; j < array.length(); j++) {
tags[j] = array.getString(j);
}
for (String tag : tags) {
if (tag.equals(this.tag))
{
Post additive = new Post(img, title, subtitle,
commentCount, content, date, ID, slug, tags);
magazines.add(additive);
Log.d("SplashActivity", additive.toString());
}
}
}
} catch (JSONException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return magazines;
}
StoryListActivity 第 27 行：
public void loadItems() {
(findViewById(R.id.progress_bar)).setVisibility(View.GONE);
getSupportFragmentManager().beginTransaction()
.replace(R.id.loading, new StoryListFragment()).commit();
}
StoryItemsActivity（MagazinePagesActivity 和 StoryListActivity 扩展此类；此类扩展 JSONItemsActivity，SplashActivity 也扩展）：
package com.dailybruin.bruinframework.channels;
import java.util.ArrayList;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import com.dailybruin.bruinframework.R;
import com.dailybruin.bruinframework.base.BaseActivity;
import com.dailybruin.bruinframework.base.URLBuilder;
import android.os.Bundle;
public abstract class StoryItemsActivity extends JSONItemsActivity {
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
}
public String sourceURL()
{
return URLBuilder.getPostsURL(getString(R.string.slug));
}
public ArrayList<Item> parseJSON(String jsonString) {
// Using pre-downloaded and parsed JSON
return SplashActivity.downloadedItems;
}
}