我想将一个片段添加到以编程方式实现其布局的Activity。我查看了Fragment文档，但没有很多示例描述我需要的内容。这是我尝试编写的代码类型：
public class DebugExampleTwo extends Activity {
private ExampleTwoFragment mFragment;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
FrameLayout frame = new FrameLayout(this);
if (savedInstanceState == null) {
mFragment = new ExampleTwoFragment();
FragmentTransaction ft = getFragmentManager().beginTransaction();
ft.add(frame.getId(), mFragment).commit();
}
setContentView(frame);
}
}
...
public class ExampleTwoFragment extends Fragment {
@Override
public View onCreateView(LayoutInflater inflater,
ViewGroup container,
Bundle savedInstanceState) {
Button button = new Button(getActivity());
button.setText("Hello There");
return button;
}
}
这段代码编译但在开始时崩溃，可能是因为我的FragmentTransaction.add()不正确。这样做的正确方法是什么？
事实证明，该代码存在多个问题。片段不能以与活动相同的java文件的方式声明，而不能作为公共内部类声明。框架期望片段的构造函数（没有参数）是公共的和可见的。将片段作为内部类移动到Activity中，或者为片段创建新的java文件修复它。
第二个问题是，当您以这种方式添加片段时，必须传递对片段包含视图的引用，并且该视图必须具有自定义ID。使用默认ID会使应用程序崩溃。这是更新的代码：
public class DebugExampleTwo extends Activity {
private static final int CONTENT_VIEW_ID = 10101010;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
FrameLayout frame = new FrameLayout(this);
frame.setId(CONTENT_VIEW_ID);
setContentView(frame, new LayoutParams(
LayoutParams.MATCH_PARENT, LayoutParams.MATCH_PARENT));
if (savedInstanceState == null) {
Fragment newFragment = new DebugExampleTwoFragment();
FragmentTransaction ft = getFragmentManager().beginTransaction();
ft.add(CONTENT_VIEW_ID, newFragment).commit();
}
}
public static class DebugExampleTwoFragment extends Fragment {
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
EditText v = new EditText(getActivity());
v.setText("Hello Fragment!");
return v;
}
}
}
以下是我在阅读Tony Wong's comment后想出的内容：
public class DebugExampleTwo extends BaseActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
addFragment(android.R.id.content,
new DebugExampleTwoFragment(),
DebugExampleTwoFragment.FRAGMENT_TAG);
}
}
...
public abstract class BaseActivity extends Activity {
protected void addFragment(@IdRes int containerViewId,
@NonNull Fragment fragment,
@NonNull String fragmentTag) {
getSupportFragmentManager()
.beginTransaction()
.add(containerViewId, fragment, fragmentTag)
.disallowAddToBackStack()
.commit();
}
protected void replaceFragment(@IdRes int containerViewId,
@NonNull Fragment fragment,
@NonNull String fragmentTag,
@Nullable String backStackStateName) {
getSupportFragmentManager()
.beginTransaction()
.replace(containerViewId, fragment, fragmentTag)
.addToBackStack(backStackStateName)
.commit();
}
}
...
public class DebugExampleTwoFragment extends Fragment {
public static final String FRAGMENT_TAG =
BuildConfig.APPLICATION_ID + ".DEBUG_EXAMPLE_TWO_FRAGMENT_TAG";
// ...
}
如果您正在使用Kotlin，请务必查看Google提供的Kotlin extensions或者自己编写的内容。
public class Example1 extends FragmentActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
DemoFragment fragmentDemo = (DemoFragment)
getSupportFragmentManager().findFragmentById(R.id.frame_container);
//above part is to determine which fragment is in your frame_container
setFragment(fragmentDemo);
(OR)
setFragment(new TestFragment1());
}
// This could be moved into an abstract BaseActivity
// class for being re-used by several instances
protected void setFragment(Fragment fragment) {
FragmentManager fragmentManager = getSupportFragmentManager();
FragmentTransaction fragmentTransaction =
fragmentManager.beginTransaction();
fragmentTransaction.replace(android.R.id.content, fragment);
fragmentTransaction.commit();
}
}
要将片段添加到Activity或FramentActivity中，它需要一个Container。该容器应该是“
Framelayout”，可以包含在xml中，否则您可以使用默认容器，如“android.R.id.content”来删除或替换Activity中的片段。
main.xml中
<RelativeLayout
android:layout_width="match_parent"
android:layout_height="match_parent" >
<!-- Framelayout to display Fragments -->
<FrameLayout
android:id="@+id/frame_container"
android:layout_width="match_parent"
android:layout_height="match_parent" />
<ImageView
android:id="@+id/imagenext"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentBottom="true"
android:layout_alignParentRight="true"
android:layout_margin="16dp"
android:src="@drawable/next" />
</RelativeLayout>
阅读完所有答案后，我想出了优雅的方式：
public class MyActivity extends ActionBarActivity {
Fragment fragment ;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
FragmentManager fm = getSupportFragmentManager();
fragment = fm.findFragmentByTag("myFragmentTag");
if (fragment == null) {
FragmentTransaction ft = fm.beginTransaction();
fragment =new MyFragment();
ft.add(android.R.id.content,fragment,"myFragmentTag");
ft.commit();
}
}
基本上你不需要添加frameLayout作为片段的容器，而是可以将片段直接添加到android root视图容器中
重要提示：不要使用替换片段作为此处显示的大部分方法，除非您不介意在重新创建过程中丢失片段变量实例状态。
public abstract class SingleFragmentActivity extends Activity {
public static final String FRAGMENT_TAG = "single";
private Fragment fragment;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
if (savedInstanceState == null) {
fragment = onCreateFragment();
getFragmentManager().beginTransaction()
.add(android.R.id.content, fragment, FRAGMENT_TAG)
.commit();
} else {
fragment = getFragmentManager().findFragmentByTag(FRAGMENT_TAG);
}
}
public abstract Fragment onCreateFragment();
public Fragment getFragment() {
return fragment;
}
}
使用
public class ViewCatalogItemActivity extends SingleFragmentActivity {
@Override
public Fragment onCreateFragment() {
return new FragmentWorkShops();
}
}
对于API级别17或更高级别，View.generateViewId()将解决此问题。该实用程序方法提供了在构建时不使用的唯一ID。