通过代码在FragmentAcivity内变换Fragment遇到的一些问题
先上一段代码。
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TestFragmentActivity.java
package com.xc.fragment; import com.xc.activity.R; import android.os.Bundle; import android.support.v4.app.FragmentActivity; import android.support.v4.app.FragmentManager; import android.support.v4.app.FragmentTransaction; public class TestFragmentActivity extends FragmentActivity { @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.fragment_activity); FragmentManager fragmentManager = getSupportFragmentManager(); FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction(); fragmentTransaction.add(R.id.fragment, new TestFragment()); fragmentTransaction.commit(); } }
fragment_activity.xml
TestFragment.java
package com.xc.fragment; import android.os.Bundle; import android.support.v4.app.Fragment; import android.view.LayoutInflater; import android.view.View; import android.view.ViewGroup; import android.widget.TextView; import com.xc.activity.R; public class TestFragment extends Fragment { @Override public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { TextView view = (TextView) inflater.inflate(R.layout.fragment, null); view.setText("oooooooooo"); return view; } }
fragment.xml
1。上述代码可以正常运行。出现“oooooooooo”
2。若将TestFragment.java中的代码替换为:
View view = inflater.inflate(R.layout.fragment, null);
出现“lalall”
3。若将TestFragment.java中的代码替换为:
View view = inflater.inflate(R.layout.fragment, container);
出错:The specified child already has a parent. You must call removeView() on the child's parent first.
那么根据提示移除父组件里的子布局:
View view = inflater.inflate(R.layout.fragment, container); ((ViewGroup)view.getParent()).removeView(view);
不出错,但什么也不出现,因为view已经被移除了。
4。若将TestFragment.java中的代码替换为:
View view = inflater.inflate(R.layout.fragment, container, false);
出现“lalall”
若改为:
View view = inflater.inflate(R.layout.fragment, container, false); ((TextView)view).setText("!!!!");
出现“!!!!”
5。若将TestFragment.java中的代码替换为:
View view = inflater.inflate(R.layout.fragment, container, true);
出现和3一样的错误。true和false起到决定性作用。
6。若将TestFragment.java中的代码替换为:
View view = inflater.inflate(R.layout.fragment, container, true); ((TextView)view).setText("!!!!");
出错:android.widget.LinearLayout cannot be cast to android.widget.TextView。
若保持上述代码不动,改变fragment_acivity.xml中的代码:
出错:android.widget.RelativeLayout cannot be cast to android.widget.TextView。
这说明view已经被add到TestFragmentActivity中,并且随着父组件container变化。
7。若将fragment.xml中代码改变为:
TestFragment.java中代码改变为:
View view = inflater.inflate(R.layout.fragment, null, true);
或:
View view = inflater.inflate(R.layout.fragment, container, false);
或:
View view = inflater.inflate(R.layout.fragment, null);
都会出错:
于是改成:
View view = inflater.inflate(R.layout.fragment, container, true);
出错:The specified child already has a parent. You must call removeView() on the child's parent first。
结论:
1。看上去inflater.inflate(R.layout.fragment, null)类似于inflater.inflate(R.layout.fragment, container, false);
但是inflate方法中的viewGroup若为null,则inflate出来的view会丢失其属性,所以通常会放入viewgroup,但是attachToRoot属性设为false。
(项目中直接在xml中写ListView,用inflate(id,null)会出现卡UI的现象,但是用inflate(id,container,fale)不会加载到父类中出错,但也不会卡UI)。
2。inflater.inflate(R.layout.fragment, container, true)类似于inflater.inflate(R.layout.fragment, container)
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若activity.xml代码为:
在TestFragmentActivity.java中:
FragmentManager manager = getSupportFragmentManager(); FragmentTransaction transaction = manager.beginTransaction(); transaction.replace(R.id.fragment, new TestFragment1()); transaction.commit();
R.id.fragment指代的是xml文件中com.test.TestFragment。
加入一句代码:
FragmentManager manager = getSupportFragmentManager(); FragmentTransaction transaction = manager.beginTransaction(); transaction.replace(R.id.fragment, new TestFragment1()); transaction.addToBackStack(null); transaction.commit();
则fragment栈中保存了TestFragment和TestFragment1的关系。按返回键,会从TestFragment1回退到TestFragment。
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