使用按钮在片段之间切换

Kapparino 发表于 Dev

卡帕里诺

在我的应用程序中，我有一个活动和两个片段。我想做的是用按钮在这两个片段之间导航。每个导航按钮都在片段中定义。

第一个问题是，使用下面的代码，我在应用程序运行时遇到异常：

E/AndroidRuntime: FATAL EXCEPTION: main
        java.lang.RuntimeException: Unable to start activity ComponentInfo{...MainActivity}: 
            java.lang.IllegalArgumentException: No view found for id 0x7f0c0050 for fragment Fragment1{b41da690 #0 id=0x7f0c0050}
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2059)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2084)
        at android.app.ActivityThread.access$600(ActivityThread.java:130)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195)
        at android.os.Handler.dispatchMessage(Handler.java:99)
        at android.os.Looper.loop(Looper.java:137)
        at android.app.ActivityThread.main(ActivityThread.java:4745)
        at java.lang.reflect.Method.invokeNative(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:511)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
        at dalvik.system.NativeStart.main(Native Method)
        Caused by: java.lang.IllegalArgumentException: No view found for id 0x7f0c0050 for fragment Fragment1{b41da690 #0 id=0x7f0c0050}
        at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:823)
        at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:1035)
        at android.app.BackStackRecord.run(BackStackRecord.java:635)
        at android.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1397)
        at android.app.Activity.performStart(Activity.java:5017)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2032)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2084) 
        at android.app.ActivityThread.access$600(ActivityThread.java:130) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195) 
        at android.os.Handler.dispatchMessage(Handler.java:99) 
        at android.os.Looper.loop(Looper.java:137) 
        at android.app.ActivityThread.main(ActivityThread.java:4745) 
        at java.lang.reflect.Method.invokeNative(Native Method) 
        at java.lang.reflect.Method.invoke(Method.java:511) 
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553) 
        at dalvik.system.NativeStart.main(Native Method)

代码：

MainActivity.java

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        // set desired fragment for the first time
        setFragment(this, new Fragment1());
    }

    public void switch_fragment(View view, String fragmentID) {
        Fragment newFragment = null;
        switch (fragmentID) {
            case Fragment1.ID:
                newFragment = new Fragment1();
                break;
            case Fragment2.ID:
                newFragment = new Fragment2();
                break;
        }
        setFragment(this, newFragment);
    }

    public static void setFragment(Activity activity, Fragment fragment) {
        FragmentTransaction fragmentTransaction = activity.getFragmentManager().beginTransaction();
        fragmentTransaction.replace(R.id.fragment_placeHolder, fragment);
        fragmentTransaction.commit();
    }
}

main_activity.xml

<?xml version="1.0" encoding="utf-8"?>
<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=".MainActivity">

    <FrameLayout
        android:id="@+id/fragment_placeHolder"
        android:layout_width="match_parent"
        android:layout_height="match_parent">
    </FrameLayout>

    <fragment
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:id="@+id/fragment1"
        />
    <fragment
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:id="@+id/fragment2"
        />
</RelativeLayout>

Fragment1.java

public class Fragment1 extends Fragment {

    public static final String ID = "1";

    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        return inflater.inflate(R.layout.fragment1, container, false);
    }

}

fragment1.xml

<RelativeLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    android:paddingBottom="@dimen/activity_vertical_margin">

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="GO TO FRAGMENT 1"
        android:id="@+id/btn_1"
        android:onClick="switch_fragment"
        android:layout_alignParentBottom="true"
        android:layout_centerHorizontal="true"
        />
</RelativeLayout>

Fragment2.java

public class Fragment2 extends Fragment {

    public static final String ID = "2";

    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        return inflater.inflate(R.layout.fragment2, container, false);
    }

}

fragment2.xml

<RelativeLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    android:paddingBottom="@dimen/activity_vertical_margin">

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="GO TO FRAGMENT 2"
        android:id="@+id/btn_2"
        android:onClick="switch_fragment"
        android:layout_alignParentBottom="true"
        android:layout_centerHorizontal="true"
        />
</RelativeLayout>

如果此示例是错误的实现方式，请为新手链接一些类似的示例。

TD阮

您错过了一个非常重要的部分，setContentView并且在使用replace之前，您应该有一个现有的片段。所以在onCreate变化中：

// set desired fragment for the first time
        setFragment(this, new Fragment1());

应更改为：

   setContentView(R.layout.main_activity);//then
   // set desired fragment for the first time
   FragmentManager fm = getSupportFragmentManager();
   FragmentTransaction ft = fm.beginTransaction();

    // The id specified here identifies which ViewGroup to
    // append the Fragment to.
    ft.add(R.id.fragment_placeHolder, new Fragment1());
    ft.commit();

尝试更换：

... activity.getFragmentManager()

和：

... getSupportFragmentManager()

并删除：

<fragment
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:id="@+id/fragment1"
    />
<fragment
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:id="@+id/fragment2"
    />

最后，将更switch_fragment改为：

public void switch_fragment(View view) {
        Fragment newFragment = null;
        switch (view.getID()) {
            case R.id.btn_2:
                newFragment = new Fragment1();
                break;
            case R.id.btn_1:
                newFragment = new Fragment2();
                break;
        }
        setFragment(this, newFragment);
    }

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