應用程序無法啓動

Question

我寫了一個簡單的應用程序來顯示ListView中的數據。該應用程序沒有錯誤，但在運行時停止並且不運行。

以下是main.java文件：

public class MainActivity extends Activity { 

ArrayList<TimeRecord> times = new ArrayList<MainActivity.TimeRecord>(); 
ListView listView = (ListView) findViewById(R.id.times_list); 
TimeTrackerAdapter timeTrackerAdapter = new TimeTrackerAdapter(); 

@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_main); 
    listView.setAdapter(timeTrackerAdapter); 
} 

@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; 
} 


public class TimeRecord{ 
    private String time; 
    private String notes; 
    public TimeRecord(String time, String notes){ 
     this.time = time; 
     this.notes = notes; 
    } 
    public String getTime() {return this.time;} 
    public void setTime(String time){this.time = time;} 
    public String getNotes(){return this.notes;} 
    public void setNotes(String notes){this.notes = notes;} 
} 

public class TimeTrackerAdapter extends BaseAdapter{ 

    TimeTrackerAdapter(){ 
     times.add(new TimeRecord("38:23", "Feeling good!")); 
     times.add(new TimeRecord("49:01", "Tired. Needed more caffeine")); 
     times.add(new TimeRecord("26:21", "I’m rocking it!")); 
     times.add(new TimeRecord("29:42", "Lost some time on the hills, but pretty good.")); 
    } 

    @Override 
    public int getCount() { 
     return times.size(); 
    } 

    @Override 
    public Object getItem(int index) { 
     return times.get(index); 
    } 

    @Override 
    public long getItemId(int index){ 
     return index; 
    } 

    @Override 
    public View getView(int index, View view, ViewGroup parent) { 
     if (view == null) { 
      LayoutInflater inflater = LayoutInflater.from(parent.getContext()); 
      view = inflater.inflate(R.layout.time_list_item, parent, false); 
     } 

     TimeRecord time = times.get(index); 
     TextView timeTextView = (TextView) findViewById(R.id.time_view); 
     timeTextView.setText(time.getTime()); 
     TextView noteTextView = (TextView) findViewById(R.id.notes_view); 
     noteTextView.setText(time.getNotes()); 
     return view; 
    } 
} 

}

，這是清單的內容：

<?xml version="1.0" encoding="utf-8"?> 
    <manifest xmlns:android="http://schemas.android.com/apk/res/android" 
    package="com.example.timelistrecords" 
    android:versionCode="1" 
    android:versionName="1.0" > 

    <uses-sdk 
    android:minSdkVersion="2" 
    android:targetSdkVersion="18" /> 

    <application 
    android:icon="@drawable/ic_launcher" 
    android:label="@string/app_name" 
    android:theme="@style/AppTheme" > 
    <activity 
     android:name="com.example.timelistrecords.MainActivity" 
     android:label="@string/app_name" > 
     <intent-filter> 
      <action android:name="android.intent.action.MAIN" /> 

      <category android:name="android.intent.category.LAUNCHER" /> 
     </intent-filter> 
    </activity> 
    </application> 

    </manifest> 

我嘗試添加任何代碼之前運行的項目，它正在運行，所以我不認爲這是android版本問題。我沒有使用任何硬件，所以不應該有權限問題。 有什麼想法？

Answer 1

setContentView之後在onCreate中初始化。你可能有NullPointerException。如果您的應用在發佈堆棧跟蹤時仍存在問題。 findViewById尋找一個視圖，在當前的版圖中使用id。因此，您需要首先將佈局的內容設置爲該活動，然後初始化您的視圖。

ListView listView; 
@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_main); // fisrt 
    listView = (ListView) findViewById(R.id.times_list); // initialize listview 
    listView.setAdapter(timeTrackerAdapter); 
} 

其在getView同樣使用視圖對象初始化你的意見。

TextView timeTextView = (TextView) view.findViewById(R.id.time_view); 
TextView noteTextView = (TextView) view.findViewById(R.id.notes_view); 

你也應該考慮使用onCreate方法內ViewHolder模式

http://developer.android.com/training/improving-layouts/smooth-scrolling.html

Answer 2

ListView listView; 
@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_main); // fisrt 
    listView = (ListView) findViewById(R.id.times_list); // initialize listview 
    listView.setAdapter(timeTrackerAdapter); 
} 


public View getView(int index, View view, ViewGroup parent) { 
     if (view == null) { 
      LayoutInflater inflater = LayoutInflater.from(parent.getContext()); 
      view = inflater.inflate(R.layout.time_list_item, parent, false); 
     } 

     TimeRecord time = times.get(index); 
     TextView timeTextView = (TextView)view. findViewById(R.id.time_view);//view. here 
     timeTextView.setText(time.getTime()); 
     TextView noteTextView = (TextView)view.findViewById(R.id.notes_view);//view. here 
     noteTextView.setText(time.getNotes()); 
     return view; 
    }