[英]Android findViewById is returning Null in Eclipse generated project
我在Eclipse中使用一個Blank Activity創建了一個新的Android項目。 在該片段中,我添加了一個名為textHello的TextView。 我為此測試要做的只是修改textHello的文本值。 但是我是我的findViewById給我null。
這是片段代碼:
<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="com.example.gcuitest.MainActivity$PlaceholderFragment" >
<TextView
android:id="@+id/textHello"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="@string/hello_world" />
</RelativeLayout>
這是MainActivity.java
package com.example.gcuitest;
import android.app.Activity;
import android.app.ActionBar;
import android.app.Fragment;
import android.app.FragmentManager;
import android.app.FragmentTransaction;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;
import android.os.Build;
public class MainActivity extends Activity {
private TextView helloText;
@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();
FragmentManager fragmentManager = getFragmentManager();
FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
fragmentTransaction.add(R.id.container, new PlaceholderFragment());
fragmentTransaction.commit();
}
helloText = (TextView) findViewById(R.id.textHello);
helloText.setText("Gerard");
}
@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;
}
}
}
為什么findViewById給我null? 在正確的地方嗎? 我看過其他代碼示例,並將它們放置在setContentView之后的onCreate中的findViewById上,這是這樣做的。 我錯過了什么? 謝謝。
為什么findViewById給我null?
因為textHello
TextView在PlaceholderFragment
布局內部,而不是Activity,即activity_main
。
如果要從Fragment布局訪問TextView,請使用onCreateView
作為:
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.fragment_layout, container, false);
helloText = (TextView)view. findViewById(R.id.textHello);
helloText.setText("Gerard");
return view;
}
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