[英]TextView is null after setContentView
我在這里查看了幾個類似的問題,但沒有一個問題解釋了我的問題。 我只是試圖通過id引用TextView,但是無論何時嘗試對其進行操作,我都會不斷收到Null Pointer Exceptions。 我確保在兩個setContentView()都被調用並且片段被誇大之后放置我的作業。 為了確保沒有其他原因導致問題,我刪除了代碼的其他部分,並在分配后立即測試了null。 無論如何,它仍然顯示為null。
這是我的代碼:
public class MainActivity extends Activity
{
//MEMBER VARIABLES
TextView mQuestionText;
@Override
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();
}
mQuestionText = (TextView) findViewById(R.id.questionTextView);
if (mQuestionText == null)
System.out.println("debug:: " + "null");
}
@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;
}
@Override
public boolean onOptionsItemSelected(MenuItem item)
{
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
if (id == R.id.action_settings)
{
return true;
}
return super.onOptionsItemSelected(item);
}
/**
* A placeholder fragment containing a simple view.
*/
public static class PlaceholderFragment extends Fragment
{
public PlaceholderFragment()
{
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState)
{
View rootView = inflater.inflate(R.layout.fragment_main, container,
false);
return rootView;
}
}
}
這是fragment_main.xml:
<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="edu.wichita.eecs.cs697ac.w387u669.assignment3.MainActivity$PlaceholderFragment" >
<TextView
android:id="@+id/questionTextView"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentTop="true"
android:layout_centerHorizontal="true"
android:layout_marginTop="41dp"
android:text="Question"
android:textAppearance="?android:attr/textAppearanceLarge" />
<Button
android:id="@+id/button2"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignBottom="@+id/button1"
android:layout_toRightOf="@+id/questionTextView"
android:text="False" />
<Button
android:id="@+id/button1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_below="@+id/questionTextView"
android:layout_marginTop="35dp"
android:layout_toLeftOf="@+id/questionTextView"
android:text="True" />
</RelativeLayout>
謝謝你的幫助!
編輯:在進行了一些其他研究之后,我了解到可以覆蓋onStart()方法並將代碼移到那里,因為我可以訪問視圖(甚至是片段中的視圖)。 但是,這只是一個旁路,實際上並沒有真正使用片段,而是要使用片段。
protected void onStart()
{
super.onStart();
TextView test = (TextView) findViewById(R.id.questionTextView);
test.setText("hello");
}
希望可以幫助某人
questionTextView
TextView在PlaceholderFragment
fragment_main.xml
布局中,因此使用Fragment的onCreateView
將TextView初始化為:
View rootView = inflater.inflate(R.layout.fragment_main, container,
false);
TextView mQuestionText = (TextView)rootView.findViewById(R.id.questionTextView);
如果您使用的是片段,則應從片段的OnCreateView方法中引用它
公共類MainActivity擴展了Activity {
@Override 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(); } } @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; } @Override public boolean onOptionsItemSelected(MenuItem item) { // Handle action bar item clicks here. The action bar will // automatically handle clicks on the Home/Up button, so long // as you specify a parent activity in AndroidManifest.xml. int id = item.getItemId(); if (id == R.id.action_settings) { return true; } return super.onOptionsItemSelected(item); } /** * A placeholder fragment containing a simple view. */ public static class PlaceholderFragment extends Fragment { public PlaceholderFragment() { } @Override public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { View rootView = inflater.inflate(R.layout.fragment_main, container, false); TextView QuestionText = (TextView) rootView.findViewById(R.id.questionTextView); if (mQuestionText == null) System.out.println("debug:: " + "null"); return rootView; } } }
您已經設置了setContentView(R.layout.activity_main)
但是您的xml名稱是fragment_main.xml。在setContentView中使用此XML,即setContentView(R.layout.fragment_main)
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