我使用 fragment 更改了三个选项卡中的 activity_main.xml 布局。我想像以前一样访问 MainActivity 中的所有选项卡组件，但出现 NullPointersException。我在这里做错了什么。谢谢!
我的 fragment 代码:
import android.app.Fragment;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.EditText;
public class FragMent3 extends Fragment {
EditText textBox;
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.logbook_view, null);
return view;
}
}
第三个布局标签的代码:
<LinearLayout 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" >
<Button android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Send request"
android:onClick="onSendButtonClicked" />
<EditText
android:id="@+id/editText1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:hint="Write request.."
android:ems="10" />
</LinearLayout>
MainActivity 部分代码:
@SuppressLint("NewApi")
public class MainActivity extends Activity implements TabListener {
RelativeLayout rl;
EditText textBox;
static int x;
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
textBox = (EditText)findViewById(R.id.editText1);
try {
rl = (RelativeLayout) findViewById(R.id.mainLayout);
fragMentTra = getFragmentManager().beginTransaction();
ActionBar bar = getActionBar();
bar.addTab(bar.newTab().setText("Info").setTabListener(this));
bar.addTab(bar.newTab().setText("Pilot").setTabListener(this));
bar.addTab(bar.newTab().setText("Logbook").setTabListener(this));
bar.setDisplayOptions(ActionBar.DISPLAY_SHOW_CUSTOM
| ActionBar.DISPLAY_USE_LOGO);
bar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);
bar.setDisplayShowHomeEnabled(true);
bar.setDisplayShowTitleEnabled(false);
bar.show();
} catch (Exception e) {
e.getMessage();
}
/**
* Hiding Action Bar
*/
}
FragMent1 fram1;
FragmentTransaction fragMentTra = null;
FragMent2 fram2;
FragMent3 fram3;
/*
@Override
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.activity_main, menu);
return true;
}*/
@Override
public void onTabReselected(Tab tab, FragmentTransaction ft) {
}
@Override
public void onTabSelected(Tab tab, FragmentTransaction ft) {
if (tab.getText().equals("Info")) {
try {
rl.removeAllViews();
} catch (Exception e) {
}
fram1 = new FragMent1();
fragMentTra.addToBackStack(null);
fragMentTra = getFragmentManager().beginTransaction();
fragMentTra.add(rl.getId(), fram1);
fragMentTra.commit();
} else if (tab.getText().equals("Pilot")) {
try {
rl.removeAllViews();
} catch (Exception e) {
}
fram2 = new FragMent2();
fragMentTra.addToBackStack(null);
fragMentTra = getFragmentManager().beginTransaction();
fragMentTra.add(rl.getId(), fram2);
fragMentTra.commit();
} else if (tab.getText().equals("Logbook")) {
try {
rl.removeAllViews();
} catch (Exception e) {
}
fram3 = new FragMent3();
fragMentTra.addToBackStack(null);
fragMentTra = getFragmentManager().beginTransaction();
fragMentTra.add(rl.getId(), fram3);
fragMentTra.commit();
}
}
@Override
public void onTabUnselected(Tab tab, FragmentTransaction ft) {
}
public void onSendButtonClicked(View view) {
textBox.setText("some text on third tab EditText");
}
日志:
05-06 12:42:19.993: E/AndroidRuntime(29991): FATAL EXCEPTION: main
05-06 12:42:19.993: E/AndroidRuntime(29991): java.lang.IllegalStateException: Could not execute method of the activity
05-06 12:42:19.993: E/AndroidRuntime(29991): at android.view.View$1.onClick(View.java:3103)
05-06 12:42:19.993: E/AndroidRuntime(29991): at android.view.View.performClick(View.java:3574)
05-06 12:42:19.993: E/AndroidRuntime(29991): at android.view.View$PerformClick.run(View.java:14293)
05-06 12:42:19.993: E/AndroidRuntime(29991): at android.os.Handler.handleCallback(Handler.java:605)
05-06 12:42:19.993: E/AndroidRuntime(29991): at android.os.Handler.dispatchMessage(Handler.java:92)
05-06 12:42:19.993: E/AndroidRuntime(29991): at android.os.Looper.loop(Looper.java:137)
05-06 12:42:19.993: E/AndroidRuntime(29991): at android.app.ActivityThread.main(ActivityThread.java:4441)
05-06 12:42:19.993: E/AndroidRuntime(29991): at java.lang.reflect.Method.invokeNative(Native Method)
05-06 12:42:19.993: E/AndroidRuntime(29991): at java.lang.reflect.Method.invoke(Method.java:511)
05-06 12:42:19.993: E/AndroidRuntime(29991): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:823)
05-06 12:42:19.993: E/AndroidRuntime(29991): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:590)
05-06 12:42:19.993: E/AndroidRuntime(29991): at dalvik.system.NativeStart.main(Native Method)
05-06 12:42:19.993: E/AndroidRuntime(29991): Caused by: java.lang.reflect.InvocationTargetException
05-06 12:42:19.993: E/AndroidRuntime(29991): at java.lang.reflect.Method.invokeNative(Native Method)
05-06 12:42:19.993: E/AndroidRuntime(29991): at java.lang.reflect.Method.invoke(Method.java:511)
05-06 12:42:19.993: E/AndroidRuntime(29991): at android.view.View$1.onClick(View.java:3098)
05-06 12:42:19.993: E/AndroidRuntime(29991): ... 11 more
05-06 12:42:19.993: E/AndroidRuntime(29991): Caused by: java.lang.NullPointerException
05-06 12:42:19.993: E/AndroidRuntime(29991): at com.example.colibri2bbui.MainActivity.onSendButtonClicked(MainActivity.java:201)
05-06 12:42:19.993: E/AndroidRuntime(29991): ... 14 more
最佳答案
您执行“TAB”实现的方式完全错误。首先，你应该使用 FrameLayout作为父 View 添加/替换您的 Fragments .第二件事是 onTabSelected 中的逻辑应该改变。下面是一个示例，它是在 ActionBar 中使用 Tab Navigation 的正确方法。
首先创建您的 main.xml，您的 fragment 将添加/附加到其中:
<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/fragment_container"
android:layout_width="match_parent"
android:layout_height="match_parent" />
其次，您可以创建选项卡并添加 TabListener对他们:
mMyActionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);
ActionBar.Tab mFirstTab = mMyActionBar.newTab();
mFirstTab.setText("First Tab");
mFirstTab.setTabListener(this);
mMyActionBar.addTab(mFirstTab);
ActionBar.Tab mSecondTab = mMyActionBar.newTab();
mSecondTab.setText("Second Tab");
mSecondTab.setTabListener(this);
mMyActionBar.addTab(mSecondTab);
ActionBar.Tab mThirdTab = mMyActionBar.newTab();
mThirdTab.setText("Third Tab");
mThirdTab.setTabListener(this);
mMyActionBar.addTab(mThirdTab);
并像这样创建你的 TabListener :
public void onTabSelected(Tab tab, FragmentTransaction ft) {
// Check if the fragment is already initialized
if (mFirstTab == null) {
// If not, instantiate and add it to the activity
mFirstTab = Fragment.instantiate(mActivity, mClass.getName());
ft.add(android.R.id.content, mFirstTab, mTag);
} else {
// If it exists, simply attach it in order to show it
ft.attach(mFirstTab);
}
}
public void onTabUnselected(Tab tab, FragmentTransaction ft) {
if (mFirstTab != null) {
// Detach the fragment, because another one is being attached
ft.detach(mFirstTab);
}
}
public void onTabReselected(Tab tab, FragmentTransaction ft) {
// User selected the already selected tab. Usually do nothing.
}
关于NullPointerException在你的代码中，我可以看到你的 EditText : textBox = (EditText)findViewById(R.id.editText1);你正试图在你的 MainActivity 中使用它在您的第三个选项卡布局中声明。这EditText应在您的 FragMent3 中声明和使用, 不在 MainActivity .
希望这个回答对你有帮助!
关于java - 访问 Activity fragment 上的布局组件？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/16396755/