Android 中 Fragment 的基本使用

1. 基础了解

Fragment 有自己的生命周期

Fragment 依赖于 Activity

Fragment 通过 getActivity() 可以获取所在的 Activity; Activity 通过 FragmentManager 的 findFragmentById()
或 findFragmentByTag() 获取 Fragment

Fragment 和 Activity 是多对多的关系

2. 了解使用

Activity 嵌一个 Fragment, 点击按钮切换另一个.

在这里插入图片描述

ContainerActivity 文件

package com.example.hello.fragment;

import androidx.appcompat.app.AppCompatActivity;
import androidx.fragment.app.Fragment;

import android.os.Bundle;
import android.widget.Button;

import com.example.hello.R;

public class ContainerActivity extends AppCompatActivity {
    
    

    private AFragment aFragment;
    private BFragment bFragment;
    private Button btnChange;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
    
    
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_container);

        btnChange = findViewById(R.id.btn_change_fragment);
        btnChange.setOnClickListener(v -> {
    
    
            // 切换
            if (bFragment == null) {
    
    
                bFragment = new BFragment();
            }
            // 防止实例
            Fragment fragment = getSupportFragmentManager().findFragmentByTag("a");
            if (fragment != null) {
    
    
                getSupportFragmentManager().beginTransaction().hide(fragment).add(R.id.content_fragment, bFragment).addToBackStack(null).commitAllowingStateLoss();
            } else {
    
    
                getSupportFragmentManager().beginTransaction().replace(R.id.content_fragment, bFragment).addToBackStack(null).commitAllowingStateLoss();
            }
        });

        // 实例化
        aFragment = new AFragment("参数");
        // 将 aFragment 放入到 Activity 中
        getSupportFragmentManager().beginTransaction().add(R.id.content_fragment, aFragment, "a").commitAllowingStateLoss();
    }
}

activity_container.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:padding="15dp"
    tools:context=".fragment.ContainerActivity">

    <Button
        android:id="@+id/btn_change_fragment"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="@string/changeFragment" />

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

</LinearLayout>

AFragment

package com.example.hello.fragment;

import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;

import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.fragment.app.Fragment;

import com.example.hello.R;

public class AFragment extends Fragment {
    
    

    private TextView tvA;

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

    @Override
    public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
    
    
        super.onViewCreated(view, savedInstanceState);
        tvA = view.findViewById(R.id.fragment_tv);
    }
}

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:padding="15dp">

    <TextView
        android:id="@+id/fragment_tv"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:gravity="center"
        android:text="@string/fragmentA"
        android:textColor="@color/black"
        android:textSize="20sp" />

</LinearLayout>

BFragment

package com.example.hello.fragment;

import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;

import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.fragment.app.Fragment;

import com.example.hello.R;

public class BFragment extends Fragment {
    
    

    private TextView tvB;

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

    @Override
    public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
    
    
        super.onViewCreated(view, savedInstanceState);
        tvB = view.findViewById(R.id.fragment_tv);
        
    }
}

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:padding="15dp">

    <TextView
        android:id="@+id/fragment_tv"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:gravity="center"
        android:text="@string/fragmentB"
        android:textColor="@color/black"
        android:textSize="20sp" />

</LinearLayout>

在这里插入图片描述

3. 传递参数

向 Fragment 传递参数.
新版本的可以用构造函数.

在这里插入图片描述

        // 实例化
        aFragment = new AFragment("参数");

AFragment

package com.example.hello.fragment;

import android.content.Context;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;

import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.fragment.app.Fragment;

import com.example.hello.R;

public class AFragment extends Fragment {
    
    

    private TextView tvA;
    private String title;

    public AFragment(String title) {
    
    
        this.title = title;
    }

    public AFragment() {
    
    
    }

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

    @Override
    public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
    
    
        super.onViewCreated(view, savedInstanceState);
        tvA = view.findViewById(R.id.fragment_tv);
        if (title != null) {
    
    
            tvA.setText(title);
        }
    }

    @Override
    public void onAttach(@NonNull Context context) {
    
    
        super.onAttach(context);
    }

    @Override
    public void onDetach() {
    
    
        super.onDetach();
    }
}

在这里插入图片描述

4. Fragment 和 Activity 的通信

AFragment 文件

package com.example.hello.fragment;

import android.content.Context;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.TextView;

import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.fragment.app.Fragment;

import com.example.hello.R;

public class AFragment extends Fragment {
    
    

    private TextView tvA;
    private Button btnChangeContent;
    private String title;
    private ChangeContent changeContent;

    public AFragment(String title) {
    
    
        this.title = title;
    }

    public AFragment() {
    
    
    }

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

    @Override
    public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
    
    
        super.onViewCreated(view, savedInstanceState);
        tvA = view.findViewById(R.id.fragment_tv);
        if (title != null) {
    
    
            tvA.setText(title);
        }
        btnChangeContent = view.findViewById(R.id.btn_change_content);
        btnChangeContent.setOnClickListener(v -> {
    
    
            changeContent.setContent("改变的内容");
        });
    }

    @Override
    public void onAttach(@NonNull Context context) {
    
    
        super.onAttach(context);
        try {
    
    
            // 没有实现该接口会报错
            changeContent = (ChangeContent) context;
        } catch (Exception e) {
    
    
            e.printStackTrace();
        }
    }

    @Override
    public void onDetach() {
    
    
        super.onDetach();
    }

    /**
     * 通信
     */
    public interface ChangeContent {
    
    
        void setContent(String title);
    }
}

fragment_a.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:padding="15dp">

    <Button
        android:id="@+id/btn_change_content"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="@string/changeContent" />

    <TextView
        android:id="@+id/fragment_tv"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:gravity="center"
        android:text="@string/fragmentA"
        android:textColor="@color/black"
        android:textSize="20sp" />

</LinearLayout>

ContainerActivity 文件实现 AFragment 中接口进行通信.

package com.example.hello.fragment;

import androidx.appcompat.app.AppCompatActivity;
import androidx.fragment.app.Fragment;

import android.os.Bundle;
import android.widget.Button;

import com.example.hello.R;

public class ContainerActivity extends AppCompatActivity implements AFragment.ChangeContent {
    
    

    private AFragment aFragment;
    private BFragment bFragment;
    private Button btnChange;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
    
    
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_container);

        btnChange = findViewById(R.id.btn_change_fragment);
        btnChange.setOnClickListener(v -> {
    
    
            // 切换
            if (bFragment == null) {
    
    
                bFragment = new BFragment();
            }
            // 防止实例
            Fragment fragment = getSupportFragmentManager().findFragmentByTag("a");
            if (fragment != null) {
    
    
                getSupportFragmentManager().beginTransaction().hide(fragment).add(R.id.content_fragment, bFragment).addToBackStack(null).commitAllowingStateLoss();
            } else {
    
    
                getSupportFragmentManager().beginTransaction().replace(R.id.content_fragment, bFragment).addToBackStack(null).commitAllowingStateLoss();
            }
        });

        // 实例化
        aFragment = new AFragment("参数");
        // 将 aFragment 放入到 Activity 中
        getSupportFragmentManager().beginTransaction().add(R.id.content_fragment, aFragment, "a").commitAllowingStateLoss();
    }

    /**
     * 改变内容
     *
     * @param title 内容
     */
    @Override
    public void setContent(String title) {
    
    
        btnChange.setText(title);
    }
}

在这里插入图片描述

Android 中 Fragment 的基本使用

Android 中 Fragment 的基本使用

1. 基础了解

2. 了解使用

3. 传递参数

4. Fragment 和 Activity 的通信

猜你喜欢