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在android studio中无法找到符号的错误[英] Cannot find symbol error in android studio

 

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问题描述

我正在尝试将片段添加到导航抽屉中.但是我有错误:找不到符号类片段.

i添加:导入android.support.v4.app.fragment

还添加片段对象(片段片段)

错误在哪里? 我该怎么办?

home.java 

package com.example.eatit;

import android.os.Bundle;

import com.google.android.material.floatingactionbutton.FloatingActionButton;
import com.google.android.material.snackbar.Snackbar;

import android.view.View;

import androidx.core.view.GravityCompat;
import androidx.appcompat.app.ActionBarDrawerToggle;

import android.view.MenuItem;

import com.google.android.material.navigation.NavigationView;

import androidx.drawerlayout.widget.DrawerLayout;

import androidx.appcompat.app.AppCompatActivity;
import androidx.appcompat.widget.Toolbar;

import android.view.Menu;
import android.support.v4.app.Fragment;

public class Home extends AppCompatActivity
        implements NavigationView.OnNavigationItemSelectedListener {
    Fragment fragment = null;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_home);
        Toolbar toolbar = findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);
        FloatingActionButton fab = findViewById(R.id.fab);
        fab.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
                        .setAction("Action", null).show();
            }
        });
        DrawerLayout drawer = findViewById(R.id.drawer_layout);
        NavigationView navigationView = findViewById(R.id.nav_view);
        ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(
                this, drawer, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close);
        drawer.addDrawerListener(toggle);
        toggle.syncState();
        navigationView.setNavigationItemSelectedListener(this);
    }

    @Override
    public void onBackPressed() {
        DrawerLayout drawer = findViewById(R.id.drawer_layout);
        if (drawer.isDrawerOpen(GravityCompat.START)) {
            drawer.closeDrawer(GravityCompat.START);
        } else {
            super.onBackPressed();
        }
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.home, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }

    @SuppressWarnings("StatementWithEmptyBody")
    @Override
    public boolean onNavigationItemSelected(MenuItem item) {
        /* Handle navigation view item clicks here. */
        int id = item.getItemId();

        if (id == R.id.nav_home) {
            // Handle the camera action
        } else if (id == R.id.nav_gallery) {

        } else if (id == R.id.nav_slideshow) {

        } else if (id == R.id.nav_tools) {

        } else if (id == R.id.nav_share) {

        } else if (id == R.id.nav_send) {

        }

        DrawerLayout drawer = findViewById(R.id.drawer_layout);
        drawer.closeDrawer(GravityCompat.START);
        return true;
    }
}

build.grandle 

apply plugin: 'com.android.application'

android {
    compileSdkVersion 29
    buildToolsVersion "29.0.0"
    defaultConfig {
        applicationId "com.example.eatit"
        minSdkVersion 16
        targetSdkVersion 29
        versionCode 1
        versionName "1.0"
        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
        vectorDrawables.useSupportLibrary = true
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
        }
    }
}

dependencies {
    implementation fileTree(dir: 'libs', include: ['*.jar'])
    implementation 'androidx.appcompat:appcompat:1.0.2'
    implementation 'androidx.constraintlayout:constraintlayout:1.1.3'
    implementation 'com.google.firebase:firebase-database:16.0.4'
    implementation 'androidx.legacy:legacy-support-v4:1.0.0'
    implementation 'com.google.android.material:material:1.0.0'
    testİmplementation 'junit:junit:4.12'
    androidTestİmplementation 'androidx.test:runner:1.2.0'
    androidTestİmplementation 'androidx.test.espresso:espresso-core:3.2.0'
    implementation 'com.google.firebase:firebase-core:17.0.0'
    implementation 'com.google.firebase:firebase-core:10.2.0'
    implementation 'com.google.firebase:firebase-database:17.0.0'
    implementation 'info.hoang8f:fbutton:1.0.5'
    implementation 'com.rengwuxian.materialedittext:library:2.1.4'

    implementation 'androidx.cardview:cardview:1.0.0'
    implementation 'androidx.recyclerview:recyclerview:1.0.0'
    implementation 'com.squareup.picasso:picasso:2.5.2'
    implementation 'com.firebaseui:firebase-ui-database:1.2.0'
    //noinspection GradleCompatible
    implementation 'com.android.support:design:26.+'

    def nav_version = "2.1.0-alpha06"

    // Java
    implementation "androidx.navigation:navigation-fragment:$nav_version"
    implementation "androidx.navigation:navigation-ui:$nav_version"
}
apply plugin: 'com.google.gms.google-services'
apply plugin: "androidx.navigation.safeargs"

我试图搜索网络和论坛，但到目前为止，我没有找到任何有用的东西.

非常感谢.

推荐答案

在配置项目以使用Androidx时，您正在从旧的Android支持库(android.support.v<x>)导入Fragment，因此请确保您正在导入并使用正确的库.

请访问此链接找到正确的导入Fragment.

用android.support.v4.app.Fragment androidx.fragment.app.Fragment android.support.v4.app.Fragment.

其他推荐答案

更改:

import androidx.core.app.Fragment;
import androidx.core.app.FragmentManager;
import androidx.core.app.FragmentPagerAdapter;

to:

import androidx.fragment.app.Fragment;
import androidx.fragment.app.FragmentManager;
import androidx.fragment.app.FragmentPagerAdapter;

来源: https://developer.android.com/reference/androidx/fragment/app/package-summary

更新:您必须通过重构自动更新到Androidx，此后，有些人不会自动更新，需要手动执行(复制，过去)，更多信息:

I added: import android.support.v4.app.Fragment

Also add the fragment object(Fragment fragment)

Where is the mistake? What should I do?

Home.java

package com.example.eatit;

import android.os.Bundle;

import com.google.android.material.floatingactionbutton.FloatingActionButton;
import com.google.android.material.snackbar.Snackbar;

import android.view.View;

import androidx.core.view.GravityCompat;
import androidx.appcompat.app.ActionBarDrawerToggle;

import android.view.MenuItem;

import com.google.android.material.navigation.NavigationView;

import androidx.drawerlayout.widget.DrawerLayout;

import androidx.appcompat.app.AppCompatActivity;
import androidx.appcompat.widget.Toolbar;

import android.view.Menu;
import android.support.v4.app.Fragment;

public class Home extends AppCompatActivity
        implements NavigationView.OnNavigationItemSelectedListener {
    Fragment fragment = null;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_home);
        Toolbar toolbar = findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);
        FloatingActionButton fab = findViewById(R.id.fab);
        fab.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
                        .setAction("Action", null).show();
            }
        });
        DrawerLayout drawer = findViewById(R.id.drawer_layout);
        NavigationView navigationView = findViewById(R.id.nav_view);
        ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(
                this, drawer, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close);
        drawer.addDrawerListener(toggle);
        toggle.syncState();
        navigationView.setNavigationItemSelectedListener(this);
    }

    @Override
    public void onBackPressed() {
        DrawerLayout drawer = findViewById(R.id.drawer_layout);
        if (drawer.isDrawerOpen(GravityCompat.START)) {
            drawer.closeDrawer(GravityCompat.START);
        } else {
            super.onBackPressed();
        }
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.home, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }

    @SuppressWarnings("StatementWithEmptyBody")
    @Override
    public boolean onNavigationItemSelected(MenuItem item) {
        /* Handle navigation view item clicks here. */
        int id = item.getItemId();

        if (id == R.id.nav_home) {
            // Handle the camera action
        } else if (id == R.id.nav_gallery) {

        } else if (id == R.id.nav_slideshow) {

        } else if (id == R.id.nav_tools) {

        } else if (id == R.id.nav_share) {

        } else if (id == R.id.nav_send) {

        }

        DrawerLayout drawer = findViewById(R.id.drawer_layout);
        drawer.closeDrawer(GravityCompat.START);
        return true;
    }
}

build.grandle

apply plugin: 'com.android.application'

android {
    compileSdkVersion 29
    buildToolsVersion "29.0.0"
    defaultConfig {
        applicationId "com.example.eatit"
        minSdkVersion 16
        targetSdkVersion 29
        versionCode 1
        versionName "1.0"
        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
        vectorDrawables.useSupportLibrary = true
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
        }
    }
}

dependencies {
    implementation fileTree(dir: 'libs', include: ['*.jar'])
    implementation 'androidx.appcompat:appcompat:1.0.2'
    implementation 'androidx.constraintlayout:constraintlayout:1.1.3'
    implementation 'com.google.firebase:firebase-database:16.0.4'
    implementation 'androidx.legacy:legacy-support-v4:1.0.0'
    implementation 'com.google.android.material:material:1.0.0'
    testİmplementation 'junit:junit:4.12'
    androidTestİmplementation 'androidx.test:runner:1.2.0'
    androidTestİmplementation 'androidx.test.espresso:espresso-core:3.2.0'
    implementation 'com.google.firebase:firebase-core:17.0.0'
    implementation 'com.google.firebase:firebase-core:10.2.0'
    implementation 'com.google.firebase:firebase-database:17.0.0'
    implementation 'info.hoang8f:fbutton:1.0.5'
    implementation 'com.rengwuxian.materialedittext:library:2.1.4'

    implementation 'androidx.cardview:cardview:1.0.0'
    implementation 'androidx.recyclerview:recyclerview:1.0.0'
    implementation 'com.squareup.picasso:picasso:2.5.2'
    implementation 'com.firebaseui:firebase-ui-database:1.2.0'
    //noinspection GradleCompatible
    implementation 'com.android.support:design:26.+'

    def nav_version = "2.1.0-alpha06"

    // Java
    implementation "androidx.navigation:navigation-fragment:$nav_version"
    implementation "androidx.navigation:navigation-ui:$nav_version"
}
apply plugin: 'com.google.gms.google-services'
apply plugin: "androidx.navigation.safeargs"

I've tried to search the web and forums but so far I didn't find anything helpful.

Thank You so much.

推荐答案

You are importing Fragment from the old Android Support library (android.support.v<x>) while you’ve configured your project to use AndroidX, so make sure you are importing and using the correct library.

Please visit this link to find the correct import for Fragment.

Replace android.support.v4.app.Fragment with androidx.fragment.app.Fragment.

其他推荐答案

change:

import androidx.core.app.Fragment;
import androidx.core.app.FragmentManager;
import androidx.core.app.FragmentPagerAdapter;

to:

import androidx.fragment.app.Fragment;
import androidx.fragment.app.FragmentManager;
import androidx.fragment.app.FragmentPagerAdapter;

source: https://developer.android.com/reference/androidx/fragment/app/package-summary

update: you must update to androidx automatically by refactor and after that some will don't update automatically, need to do it manually(copy,past), more information: https://developer.android.com/jetpack/androidx/migrate

其他推荐答案

Add this line to your Build.gradle file:

implementation "com.android.support:support-v4:{latest_version}"

Example: 

implementation "com.android.support:support-v4:26.+"
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