我有一個幾乎完全的香草應用程序。我所要做的只是改變textView的文本,但它給了我一個NullPointerException。我沒有XML配置,沒有添加方法,沒有什麼特別的。我檢查了我的類,它指向了正確的XML,並且XML中有一個textView元素,並帶有正確的ID。textView setText()NullPointerException
我也嘗試在類級別上創建onCreate()之外的textView實例,並且應用程序無論如何都無法啓動。我確信我忽略了簡單,但我找不到答案。謝謝您的幫助。 編輯: 我意識到我需要,使其訪問片段資源遷此代碼,但是當我做,它給了我一個錯誤:
不能使靜態參考非靜態方法findViewById(INT)從類型活動
如果我的所有視圖都在我的片段中,而不在我的活動XML中,我應該在哪裏放置代碼?或者我應該只是將活動加載到片段開頭? package com.example.testapp;
import android.support.v7.app.ActionBarActivity;
import android.support.v7.app.ActionBar;
import android.support.v4.app.Fragment;
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 ActionBarActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
TextView tv = (TextView) findViewById(R.id.textView1);
tv.setText("Teststring");
if (savedInstanceState == null) {
getSupportFragmentManager().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);
}
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;
}
}
}
錯誤日誌:
06-14 17:02:27.405: E/AndroidRuntime(1420): FATAL EXCEPTION: main
06-14 17:02:27.405: E/AndroidRuntime(1420): Process: com.example.testapp, PID: 1420
06-14 17:02:27.405: E/AndroidRuntime(1420): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.testapp/com.example.testapp.MainActivity}: java.lang.NullPointerException
06-14 17:02:27.405: E/AndroidRuntime(1420): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2195)
06-14 17:02:27.405: E/AndroidRuntime(1420): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
06-14 17:02:27.405: E/AndroidRuntime(1420): at android.app.ActivityThread.access$800(ActivityThread.java:135)
06-14 17:02:27.405: E/AndroidRuntime(1420): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
06-14 17:02:27.405: E/AndroidRuntime(1420): at android.os.Handler.dispatchMessage(Handler.java:102)
06-14 17:02:27.405: E/AndroidRuntime(1420): at android.os.Looper.loop(Looper.java:136)
06-14 17:02:27.405: E/AndroidRuntime(1420): at android.app.ActivityThread.main(ActivityThread.java:5017)
06-14 17:02:27.405: E/AndroidRuntime(1420): at java.lang.reflect.Method.invokeNative(Native Method)
06-14 17:02:27.405: E/AndroidRuntime(1420): at java.lang.reflect.Method.invoke(Method.java:515)
06-14 17:02:27.405: E/AndroidRuntime(1420): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
06-14 17:02:27.405: E/AndroidRuntime(1420): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
06-14 17:02:27.405: E/AndroidRuntime(1420): at dalvik.system.NativeStart.main(Native Method)
06-14 17:02:27.405: E/AndroidRuntime(1420): Caused by: java.lang.NullPointerException
06-14 17:02:27.405: E/AndroidRuntime(1420): at com.example.testapp.MainActivity.onCreate(MainActivity.java:23)
06-14 17:02:27.405: E/AndroidRuntime(1420): at android.app.Activity.performCreate(Activity.java:5231)
06-14 17:02:27.405: E/AndroidRuntime(1420): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
06-14 17:02:27.405: E/AndroidRuntime(1420): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2159)
06-14 17:02:27.405: E/AndroidRuntime(1420): ... 11 more
XML fragment_main
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context="com.example.testapp.MainActivity$PlaceholderFragment" >
<TextView
android:id="@+id/textView1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="@string/hello_world" />
</RelativeLayout>
確保(R.id.textView1在activity_main.xml中存在 –
可以嘗試重新格式化您的代碼?刪除空行和調整一切?大多數IDE像Eclipse擁有該如CTRL + SHIFT 的快捷方式 + F –
您可以檢查textView1(區分大小寫)是否確實存在於activity_main.xml文件中?如果是這樣,請嘗試清理該項目並重新構建它。有時,在對XML文件進行大量更改後,需要重新生成R.java文件以獲得準確的ID。 – rhoadster91