为什么要在Fragment中使用setArgument？

分类：Android, Java 阅读 (2,429) Add comments

10月 272016

转载请注明原文地址：http://bcoder.com/java/why-use-setargument-in-fragment

　　我们知道，当app的屏幕进行旋转或者其他的配置变化的时候，Fragment会执行它的周期变化，重新创建Fragment并加载（除非设置了setRetainInstance(true))，那么在重建的时候Fragment中的变量就会被重新初始化，运行中的状态将无法保留。

　　setArgument中的Bundle可以用来存放各种需要保持的数据，即使Fragment由于配置改变而重建，这些保存的数据也不会被清除。

　　下面我们将通过一个实例来测试一下，在实例的Fragment中共有3个TextView和一个Button，为了使测试的内容更清晰，下面把三个TextView对应的字符串列表如下：

textview1->banana, 　　textview2->apple, 　　textview3->pear

　　对应的三个字符串：

mParam1: 在Fragment.newInstance中传入，并保存在setArgument中，但是在点击按钮时未更新到Argument中
mParam2: Fragment中的私有变量，和Argument无任何交互
mParam3: 在Fragment.newInstance中传入，并保存在setArgument中，并且在点击按钮时更新到了Argument中

　　测试程序的布局代码和java代码如下：

　　Fragment部局文件的代码

<LinearLayout 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"
              tools:context="com.bcoder.myapplication.TestFragment"
              android:orientation="vertical">

    <!-- TODO: Update blank fragment layout -->


    <TextView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="textview1"
        android:id="@+id/textview1"/>

    <TextView
        android:text="TextView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/textview2"/>

    <TextView
        android:text="TextView"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:id="@+id/textview3"/>

    <Button
        android:text="Button"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:id="@+id/button1"/>

</LinearLayout>

<LinearLayout 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"

tools:context="com.bcoder.myapplication.TestFragment"

android:orientation="vertical">

<TextView

android:layout_width="match_parent"

android:layout_height="wrap_content"

android:text="textview1"

android:id="@+id/textview1"/>

<TextView

android:text="TextView"

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:id="@+id/textview2"/>

<TextView

android:text="TextView"

android:layout_width="match_parent"

android:layout_height="wrap_content"

android:id="@+id/textview3"/>

<Button

android:text="Button"

android:layout_width="match_parent"

android:layout_height="wrap_content"

android:id="@+id/button1"/>

</LinearLayout>

　　Fragment的Java代码

package com.bcoder.myapplication;

import android.content.Context;
import android.net.Uri;
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.Button;
import android.widget.TextView;


public class TestFragment extends Fragment {
    private static final String ARG_PARAM1 = "param1";
    private static final String ARG_PARAM3 = "param3";

    private String mParam1;
    private String mParam2;
    private String mParam3;

    TextView mTextView1;
    TextView mTextView2;
    TextView mTextView3;
    Button button1;

    View fragmentView;

    public TestFragment() {
        // Required empty public constructor
    }


    public static TestFragment newInstance(String param1, String param3) {
        TestFragment fragment = new TestFragment();
        Bundle args = new Bundle();
        args.putString(ARG_PARAM1, param1);
        args.putString(ARG_PARAM3, param3);
        fragment.setArguments(args);

        return fragment;
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        if (getArguments() != null) {
            mParam1 = getArguments().getString(ARG_PARAM1);
            mParam3 = getArguments().getString(ARG_PARAM3);
        }
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        fragmentView = inflater.inflate(R.layout.fragment_test, container, false);

        initViews();

        mTextView1.setText(mParam1);
        mTextView2.setText(mParam2);
        mTextView3.setText(mParam3);

        return fragmentView;
    }

    private void initViews() {
        mTextView1 = (TextView) fragmentView.findViewById(R.id.textview1);
        mTextView2 = (TextView) fragmentView.findViewById(R.id.textview2);
        mTextView3 = (TextView) fragmentView.findViewById(R.id.textview3);

        button1 = (Button) fragmentView.findViewById(R.id.button1);
        button1.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                mParam1 = "banana2";
                mTextView1.setText(mParam1);

                mParam2 = "apple";
                mTextView2.setText(mParam2);

                mParam3 = "pear click";
                getArguments().putString(ARG_PARAM3, mParam3);
                mTextView3.setText(mParam3);
            }
        });
    }

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

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

}

package com.bcoder.myapplication;

import android.content.Context;

import android.net.Uri;

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.Button;

import android.widget.TextView;

public class TestFragment extends Fragment {

private static final String ARG_PARAM1 = "param1";

private static final String ARG_PARAM3 = "param3";

private String mParam1;

private String mParam2;

private String mParam3;

TextView mTextView1;

TextView mTextView2;

TextView mTextView3;

Button button1;

View fragmentView;

public TestFragment() {

// Required empty public constructor

}

public static TestFragment newInstance(String param1, String param3) {

TestFragment fragment = new TestFragment();

Bundle args = new Bundle();

args.putString(ARG_PARAM1, param1);

args.putString(ARG_PARAM3, param3);

fragment.setArguments(args);

return fragment;

}

@Override

public void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

if (getArguments() != null) {

mParam1 = getArguments().getString(ARG_PARAM1);

mParam3 = getArguments().getString(ARG_PARAM3);

}

@Override

public View onCreateView(LayoutInflater inflater, ViewGroup container,

Bundle savedInstanceState) {

fragmentView = inflater.inflate(R.layout.fragment_test, container, false);

initViews();

mTextView1.setText(mParam1);

mTextView2.setText(mParam2);

mTextView3.setText(mParam3);

return fragmentView;

}

private void initViews() {

mTextView1 = (TextView) fragmentView.findViewById(R.id.textview1);

mTextView2 = (TextView) fragmentView.findViewById(R.id.textview2);

mTextView3 = (TextView) fragmentView.findViewById(R.id.textview3);

button1 = (Button) fragmentView.findViewById(R.id.button1);

button1.setOnClickListener(new View.OnClickListener() {

@Override

public void onClick(View view) {

mParam1 = "banana2";

mTextView1.setText(mParam1);

mParam2 = "apple";

mTextView2.setText(mParam2);

mParam3 = "pear click";

getArguments().putString(ARG_PARAM3, mParam3);

mTextView3.setText(mParam3);

}

});

}

@Override

public void onAttach(Context context) {

super.onAttach(context);

}

@Override

public void onDetach() {

super.onDetach();

}

　　主Activity的代码

package com.bcoder.myapplication;

import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentTransaction;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.LinearLayout;

public class MainActivity extends AppCompatActivity {
    LinearLayout layoutContainer;

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

        initViews();

        TestFragment fragment = TestFragment.newInstance("banana", "pear");

        FragmentManager manager = getSupportFragmentManager();
        FragmentTransaction transaction = manager.beginTransaction();
        transaction.add(R.id.layoutFragmentContainer, fragment);
        transaction.commit();
    }

    private void initViews() {
        layoutContainer = (LinearLayout) findViewById(R.id.layoutFragmentContainer);
    }
}

package com.bcoder.myapplication;

import android.support.v4.app.FragmentManager;

import android.support.v4.app.FragmentTransaction;

import android.support.v7.app.AppCompatActivity;

import android.os.Bundle;

import android.widget.LinearLayout;

public class MainActivity extends AppCompatActivity {

LinearLayout layoutContainer;

@Override

protected void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.activity_main);

initViews();

TestFragment fragment = TestFragment.newInstance("banana", "pear");

FragmentManager manager = getSupportFragmentManager();

FragmentTransaction transaction = manager.beginTransaction();

transaction.add(R.id.layoutFragmentContainer, fragment);

transaction.commit();

}

private void initViews() {

layoutContainer = (LinearLayout) findViewById(R.id.layoutFragmentContainer);

}

　　主Activity的布局文件代码

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/activity_main"
    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="com.bcoder.myapplication.MainActivity"
    android:orientation="vertical">

    <LinearLayout
        android:orientation="vertical"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:id="@+id/layoutFragmentContainer">
    </LinearLayout>
</LinearLayout>

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

<LinearLayout

xmlns:android="http://schemas.android.com/apk/res/android"

xmlns:tools="http://schemas.android.com/tools"

android:id="@+id/activity_main"

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="com.bcoder.myapplication.MainActivity"

android:orientation="vertical">

<LinearLayout

android:orientation="vertical"

android:layout_width="match_parent"

android:layout_height="match_parent"

android:id="@+id/layoutFragmentContainer">

</LinearLayout>

　　程序启动时显示默认如下内容：

　　textview1和textview3的值取自getArgument并显示在了屏幕上，当点击按钮时会重新给三个String变量赋值，并显示到textview中，如下图：

　　这时三个字符串变量都有了新的值，那么当我们把屏幕进行一下旋转操作后，看结果如何呢？

　　由图可知，字符串1回到了最初的状态（创建Fragment时传入的值），而字符串2被清除了。

　　字符串3因为在点击按钮的时候重新被保存在getArgument中，而没有任何的变化的被保留下来了。

　　因此大家在给Fragment传入参数的时候最好通过setArgument进行保存，而不是简单的通过一个变量进行保存。

注意：

setArgument只能在Fragment中创建后(MyFragment fragment = new MyFragment())立即调用，如果在Fragment被附加到Activity中后再调用就会报错，可以在按钮的点击事件中添加一下setArgument的调用进行一下试验，应用将被异常终止。

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