未应用 Android setContentView

Question

您好，我是对上一个问题的重新提问，只是因为我之前不清楚。我有一个 json 提要，我在其中找到了数组的长度。它应该产生一个。但我想要做的是，如果要添加第二个项目，则需要使用另一个布局。

所以我目前有一个字符串，其中包含 YES 的字符串值，然后将其发送到另一个 Activity 的 Intent 中，该 Activity 被放置在一个 if 语句中，如果 x = Yes，则使用 layout1，如果 x = no，则使用 layout2。

我遇到的问题是，当我在 if 语句中放入一个字符串并记录它时，它可以正常工作，但是当我放入 setContentView 时，它会强制关闭应用程序，为什么？

这是我的代码

在第一个 Activity 中

HttpResponse response = client.execute(post);
BufferedReader reader = new BufferedReader(new InputStreamReader(response.getEntity().getContent(), "UTF-8"));
String json = reader.readLine();

JSONObject obj = new JSONObject(json);


JSONObject objData = obj.getJSONObject("data");

JSONArray jArray = objData.getJSONArray("structure");

leagueCount = jArray.length();


if (leagueCount == 1){                   
   teamFeedStructure = "YES" ; 
}        
if (leagueCount == 2){
   teamFeedStructure = "NO" ; 
}                        

现在发送 Intent

Intent mainIntent = new Intent(firstActivity.this,secondActivity.class);

mainIntent.putExtra("leagueCount", teamFeedStructure);

firstActivity.this.startActivity(mainIntent);

firstActivity.this.finish();

现在在第二个 Activity 中

@Override
protected void onCreate(Bundle savedInstanceState) {
    // TODO Auto-generated method stub
    super.onCreate(savedInstanceState);
    //setContentView(R.layout.introact);

    String leagueCount = getIntent().getExtras().getString("leagueCount");

    //String leaguecount = String.valueOf(leagueCount);

    Log.v("lc", leagueCount);

    if (leagueCount == "YES"){

        String one = "one";
        setContentView(R.layout.introact);

        Log.v("lc", one);       
    }

    //if (leaguecount == "2"){

       //setContentView(R.layout.introact);
    //}

错误

04-23 21:53:34.455: W/dalvikvm(954): threadid=1: thread exiting with uncaught exception (group=0x40015560)
04-23 21:53:34.465: E/AndroidRuntime(954): FATAL EXCEPTION: main
04-23 21:53:34.465: E/AndroidRuntime(954): java.lang.RuntimeException: Unable to start activity ComponentInfo{co.uk.fantasticmedia.TheEvoStikLeague/co.uk.fantasticmedia.TheEvoStikLeague.IntroActivity}: java.lang.NullPointerException
04-23 21:53:34.465: E/AndroidRuntime(954):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1647)
04-23 21:53:34.465: E/AndroidRuntime(954):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1663)
04-23 21:53:34.465: E/AndroidRuntime(954):  at android.app.ActivityThread.access$1500(ActivityThread.java:117)
04-23 21:53:34.465: E/AndroidRuntime(954):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:931)
04-23 21:53:34.465: E/AndroidRuntime(954):  at android.os.Handler.dispatchMessage(Handler.java:99)
04-23 21:53:34.465: E/AndroidRuntime(954):  at android.os.Looper.loop(Looper.java:130)
04-23 21:53:34.465: E/AndroidRuntime(954):  at android.app.ActivityThread.main(ActivityThread.java:3683)
04-23 21:53:34.465: E/AndroidRuntime(954):  at java.lang.reflect.Method.invokeNative(Native Method)
04-23 21:53:34.465: E/AndroidRuntime(954):  at java.lang.reflect.Method.invoke(Method.java:507)
04-23 21:53:34.465: E/AndroidRuntime(954):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
04-23 21:53:34.465: E/AndroidRuntime(954):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
04-23 21:53:34.465: E/AndroidRuntime(954):  at dalvik.system.NativeStart.main(Native Method)
04-23 21:53:34.465: E/AndroidRuntime(954): Caused by: java.lang.NullPointerException
04-23 21:53:34.465: E/AndroidRuntime(954):  at co.uk.fantasticmedia.TheEvoStikLeague.IntroActivity.onCreate(IntroActivity.java:45)
04-23 21:53:34.465: E/AndroidRuntime(954):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
04-23 21:53:34.465: E/AndroidRuntime(954):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1611)
04-23 21:53:34.465: E/AndroidRuntime(954):  ... 11 more

Answer 1

你不能使用==来比较字符串==会比较你需要做的内存位置:

 if("1".equals(leaguecount))

Top Ten Errors Java Programmers Make (见第 7 条)

将您的硬编码字符串 "1" 与 equals 方法(而不是 something.equals("1") 进行比较还可以节省您进行空检查的麻烦\

---

我认为您的问题是您发送了 null 而不是实际初始化您的字符串。在你解析你的 JSON 之后，我会这样做:

这里是一个重写:

teamFeedStructure = "NO";
if (leagueCount >= 2){
   teamFeedStructure = "YES" ; 
}

然后是你的其他 Activity

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    String leagueCount = getIntent().getStringExtra("leagueCount");
    Log.d("lc", "Received league count of:"+ leagueCount);

    if ("YES".equals(leagueCount){
        setContentView(R.layout.introact);
        Log.d("lc", "Using league count of 2 or more layout");
    }else{
        setContentView(R.layout.introact_something_else);
        Log.d("lc", "Using default layout");
    }
 }