Android編程使用Fragment界面向下跳轉并一級級返回的實現方法

2020-04-11 11:20:04

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本文實例講述了Android編程使用Fragment界面向下跳轉并一級級返回的實現方法。分享給大家供大家參考，具體如下：

1.首先貼上項目結構圖：

2.先添加一個接口文件BackHandledInterface.java,定義一個setSelectedFragment方法用于設置當前加載的Fragment在棧頂，主界面MainActivity須實現此接口，代碼如下：

package com.example.testdemo;public interface BackHandledInterface {  public abstract void setSelectedFragment(BackHandledFragment selectedFragment);}

3.定義一個抽象類BackHandledFragment繼承自Fragment，后面跳轉的Fragment界面都要繼承自BackHandledFragment。抽象類BackHandledFragment中定義一個返回值為boolean類型的onBackPressed方法，用于處理點擊返回按鍵（物理Back鍵）時的邏輯，若該方法返回false，表示當前Fragment不消費返回事件，而由Fragment所屬的FragmentActivity來處理這個事件。代碼如下：

package com.example.testdemo;import android.os.Bundle;import android.support.v4.app.Fragment;public abstract class BackHandledFragment extends Fragment {  protected BackHandledInterface mBackHandledInterface;  /**   * 所有繼承BackHandledFragment的子類都將在這個方法中實現物理Back鍵按下后的邏輯   */  protected abstract boolean onBackPressed();  @Override  public void onCreate(Bundle savedInstanceState) {    super.onCreate(savedInstanceState);    if (!(getActivity() instanceof BackHandledInterface)) {      throw new ClassCastException(          "Hosting Activity must implement BackHandledInterface");    } else {      this.mBackHandledInterface = (BackHandledInterface) getActivity();    }  }  @Override  public void onStart() {    super.onStart();    // 告訴FragmentActivity，當前Fragment在棧頂    mBackHandledInterface.setSelectedFragment(this);  }}

4.主界面MainActivity要繼承FragmentActivity才能調用getSupportFragmentManager()方法來處理Fragment。MainActivity還需重寫onBackPressed方法用來捕捉返回鍵（Back Key）事件，代碼如下：

package com.example.testdemo;import android.os.Bundle;import android.support.v4.app.FragmentActivity;import android.support.v4.app.FragmentManager;import android.support.v4.app.FragmentTransaction;import android.view.View;import android.view.View.OnClickListener;import android.widget.Button;public class MainActivity extends FragmentActivity implements    BackHandledInterface {  private static MainActivity mInstance;  private BackHandledFragment mBackHandedFragment;  private Button btnSecond;  @Override  public void onCreate(Bundle savedInstanceState) {    super.onCreate(savedInstanceState);    setContentView(R.layout.activity_main);    btnSecond = (Button) findViewById(R.id.btnSecond);    btnSecond.setOnClickListener(new OnClickListener() {      @Override      public void onClick(View v) {        FirstFragment first = new FirstFragment();        loadFragment(first);        btnSecond.setVisibility(View.GONE);      }    });  }  public static MainActivity getInstance() {    if (mInstance == null) {      mInstance = new MainActivity();    }    return mInstance;  }  public void loadFragment(BackHandledFragment fragment) {    BackHandledFragment second = fragment;    FragmentManager fm = getSupportFragmentManager();    FragmentTransaction ft = fm.beginTransaction();    ft.replace(R.id.firstFragment, second, "other");    ft.addToBackStack("tag");    ft.commit();  }  @Override  public void setSelectedFragment(BackHandledFragment selectedFragment) {    this.mBackHandedFragment = selectedFragment;  }  @Override  public void onBackPressed() {    if (mBackHandedFragment == null || !mBackHandedFragment.onBackPressed()) {      if (getSupportFragmentManager().getBackStackEntryCount() == 0) {        super.onBackPressed();      } else {        if (getSupportFragmentManager().getBackStackEntryCount() == 1) {          btnSecond.setVisibility(View.VISIBLE);        }        getSupportFragmentManager().popBackStack();      }    }  }}

5.分別添加兩個子級Fragment，FirstFragment.java和SecondFragment.java,代碼分別如下：

FirstFragment.java：

package com.example.testdemo;import android.os.Bundle;import android.support.annotation.Nullable;import android.support.v4.app.FragmentManager;import android.support.v4.app.FragmentTransaction;import android.view.LayoutInflater;import android.view.View;import android.view.View.OnClickListener;import android.view.ViewGroup;import android.widget.Button;public class FirstFragment extends BackHandledFragment {  private View myView;  private Button btnSecond;  @Override  public View onCreateView(LayoutInflater inflater,      @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {    myView = inflater.inflate(R.layout.fragment_first, null);    initView();    return myView;  }  private void initView() {    btnSecond = (Button) myView.findViewById(R.id.btnSecond);    btnSecond.setOnClickListener(new OnClickListener() {      @Override      public void onClick(View v) {        SecondFragment second = new SecondFragment();        FragmentManager fm = getFragmentManager();        FragmentTransaction ft = fm.beginTransaction();        ft.replace(R.id.firstFragment, second);        ft.addToBackStack("tag");        ft.commit();      }    });  }  @Override  protected boolean onBackPressed() {    return false;  }}

SecondFragment.java：

package com.example.testdemo;import android.os.Bundle;import android.support.annotation.Nullable;import android.view.LayoutInflater;import android.view.View;import android.view.ViewGroup;public class SecondFragment extends BackHandledFragment {  private View mView;  @Override  public View onCreateView(LayoutInflater inflater,      @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {    mView = inflater.inflate(R.layout.fragment_second, null);    return mView;  }  @Override  protected boolean onBackPressed() {    return false;  }}

6.三個布局文件代碼如下：

activity_main.xml：

<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:orientation="vertical" >  <TextView    android:layout_width="wrap_content"    android:layout_height="wrap_content"    android:layout_centerInParent="true"    android:text="FragmentActivity 父界面"    android:textSize="26sp" />  <Button    android:id="@+id/btnSecond"    android:layout_width="wrap_content"    android:layout_height="wrap_content"    android:layout_alignParentBottom="true"    android:text="跳轉到FirstFragment" />  <FrameLayout    android:id="@+id/firstFragment"    android:layout_width="match_parent"    android:layout_height="match_parent" >  </FrameLayout></RelativeLayout>

fragment_first.xml：

<?xml version="1.0" encoding="utf-8"?><RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"  android:layout_width="match_parent"  android:layout_height="match_parent"  android:background="#e5e5e5"  android:orientation="vertical" >  <TextView    android:layout_width="wrap_content"    android:layout_height="wrap_content"    android:layout_centerInParent="true"    android:text="FirstFragment"    android:textColor="#000000"    android:textSize="26sp" />  <Button    android:id="@+id/btnSecond"    android:layout_width="wrap_content"    android:layout_height="wrap_content"    android:layout_alignParentBottom="true"    android:text="打開SecondFragment" /></RelativeLayout>

fragment_second.xml：

<?xml version="1.0" encoding="utf-8"?><RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"  android:layout_width="match_parent"  android:layout_height="match_parent"  android:background="#e5e5e5"  android:orientation="vertical" >  <TextView    android:layout_width="wrap_content"    android:layout_height="wrap_content"    android:layout_centerInParent="true"    android:text="SecondFragment"    android:textColor="#000000"    android:textSize="26sp" /></RelativeLayout>

7.最后奉上實例鏈接：

完整實例代碼代碼點擊此處本站下載。

希望本文所述對大家Android程序設計有所幫助。

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