从Firebase存储中检索图像

Question

我必须使用android studio将上传到Firebase存储的图像检索到应用中以制作该应用。这基本上就像是应用程序的实时公告板，上传到Firebase存储中的图像应自动刷新到应用程序中。我是Firebase的新手，这已分配给我。谁能指导我？

我已经尝试创建Model类和ViewHolder类，并尝试了回收站视图，但是它没有响应。该应用程序始终会强制关闭。列出了存储图像的格式。

编辑（使用Recycler View的代码） activity_notices.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"
    tools:context=".Notices"
    android:orientation="vertical">

<androidx.recyclerview.widget.RecyclerView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:id="@+id/recyclerview">
</androidx.recyclerview.widget.RecyclerView>

</LinearLayout>

Model.java

package com.example.finalapkx;

public class Model {

    String title,image,description;
    public Model() {}

    public String getTitle() {
        return title;
    }

    public void setTitle(String title) {
        this.title = title;
    }

    public String getImage() {
        return image;
    }

    public void setImage(String image) {
        this.image = image;
    }

    public String getDescription() {
        return description;
    }

    public void setDescription(String description) {
        this.description = description;
    }
}

row.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.cardview.widget.CardView xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    app:cardBackgroundColor="#fff"
    app:cardCornerRadius="3dp"
    app:cardElevation="3dp"
    app:contentPadding="5dp"
    app:cardUseCompatPadding="true">


    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="vertical">

        <TextView
            android:id="@+id/rTitleTv"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:text="Title"
            android:textColor="#000"
            android:textSize="22sp"
            android:textStyle="bold" />

        <ImageView
            android:id="@+id/rImageView"
            android:layout_width="match_parent"
            android:layout_height="200dp"
            android:adjustViewBounds="true"
            android:background="@drawable/loading"
            android:scaleType="centerCrop" />
        <TextView
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:id="@+id/rDescriptionTv"
            android:text="This will be description of the Notice"
            android:textSize="20sp"
            />
    </LinearLayout>

</androidx.cardview.widget.CardView>

ViewHolder.java

package com.example.finalapkx;

import android.content.Context;
import android.view.View;
import android.widget.ImageView;
import android.widget.TextView;

import androidx.recyclerview.widget.RecyclerView;

import com.squareup.picasso.Picasso;

public class ViewHolder extends RecyclerView.ViewHolder {
    View mView;

    public ViewHolder(View itemView){
        super(itemView);


        mView = itemView;
    }
    public void setDetails(Context ctx,String title,String description, String image){
        TextView mTitleTv = mView.findViewById(R.id.rTitleTv);
        TextView mDetailTv = mView.findViewById(R.id.rDescriptionTv);
        ImageView mImageIv = mView.findViewById(R.id.rImageView);
        mTitleTv.setText(title);
        mDetailTv.setText(description);
        Picasso.get().load(image).into(mImageIv);
    }
}

Notices.java

package com.example.finalapkx;

import androidx.appcompat.app.ActionBar;
import androidx.appcompat.app.AppCompatActivity;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;

import android.os.Bundle;
import android.widget.ImageView;

import com.bumptech.glide.Glide;
import com.firebase.client.DataSnapshot;
import com.firebase.client.FirebaseError;
import com.firebase.client.ValueEventListener;
import com.firebase.client.core.Context;
import com.firebase.ui.database.FirebaseRecyclerAdapter;
import com.google.firebase.database.DatabaseReference;
import com.google.firebase.database.FirebaseDatabase;


public class Notices extends AppCompatActivity {

RecyclerView mrecyclerView;
FirebaseDatabase mfirebaseDatabase;
DatabaseReference mRef;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_notices);
        ActionBar actionBar = getSupportActionBar();
        actionBar.setTitle("Notices List");
        mrecyclerView = findViewById(R.id.recyclerview);
        mrecyclerView.setHasFixedSize(true);
        mrecyclerView.setLayoutManager(new LinearLayoutManager(this));
        mfirebaseDatabase = FirebaseDatabase.getInstance();
        mRef = mfirebaseDatabase.getReference("images");


    }

    @Override
    protected void onStart() {
        super.onStart();
        FirebaseRecyclerAdapter<Model, ViewHolder> firebaseRecyclerAdapter =
                new FirebaseRecyclerAdapter<Model, ViewHolder>(Model.class,R.layout.row,ViewHolder.class,mRef) {
                    @Override
                    protected void populateViewHolder(ViewHolder viewHolder, Model model, int i) {
                        viewHolder.setDetails(getApplicationContext(),model.getTitle(),model.getDescription(),model.getImage());

                    }
                };
           mrecyclerView.setAdapter(firebaseRecyclerAdapter);
    }
}

Logcat错误

2019-08-02 10:56:21.013 7174-7174/com.example.finalapkx E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.finalapkx, PID: 7174
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.finalapkx/com.example.finalapkx.Notices}: java.lang.NullPointerException: Attempt to invoke virtual method 'void androidx.appcompat.app.ActionBar.setTitle(java.lang.CharSequence)' on a null object reference
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2913)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3048)
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78)
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108)
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1808)
        at android.os.Handler.dispatchMessage(Handler.java:106)
        at android.os.Looper.loop(Looper.java:193)
        at android.app.ActivityThread.main(ActivityThread.java:6669)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)
     Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void androidx.appcompat.app.ActionBar.setTitle(java.lang.CharSequence)' on a null object reference
        at com.example.finalapkx.Notices.onCreate(Notices.java:32)
        at android.app.Activity.performCreate(Activity.java:7136)
        at android.app.Activity.performCreate(Activity.java:7127)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1271)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2893)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3048) 
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78) 
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108) 
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1808) 
        at android.os.Handler.dispatchMessage(Handler.java:106) 
        at android.os.Looper.loop(Looper.java:193) 
        at android.app.ActivityThread.main(ActivityThread.java:6669) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858) 
2019-08-02 10:56:21.030 7174-7174/com.example.finalapkx I/Process: Sending signal. PID: 7174 SIG: 9

Androidmanifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.finalapkx">
    <!--
         The ACCESS_COARSE/FINE_LOCATION permissions are not required to use
         Google Maps Android API v2, but you must specify either coarse or fine
         location permissions for the 'MyLocation' functionality.
    -->
    <uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />
    <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
    <uses-permission android:name="com.google.android.providers.gsf.permission.READ_GSERVICES" />
    <uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION" />
    <uses-permission android:name="android.permission.INTERNET" />

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/AppTheme"
        android:usesCleartextTraffic="true">
        <activity android:name=".AC4"></activity>
        <activity android:name=".AC3" />
        <activity android:name=".AC2" />
        <activity android:name=".AC1" />
        <activity android:name=".pdfyearone" />

        <activity android:name=".Visit" />
        <activity android:name=".Administration" />
        <activity android:name=".Leadership" />
        <activity android:name=".VisMis" />
        <activity android:name=".ACCA" />
        <activity android:name=".Genesis" />
        <activity android:name=".Results" />
        <activity android:name=".PHARMA3" />
        <activity android:name=".MECH3" />
        <activity android:name=".IT3" />
        <activity android:name=".EEE3" />
        <activity android:name=".ECE3" />
        <activity android:name=".CSE3" />
        <activity android:name=".CIVIL3" />
        <activity android:name=".CHEMICAL3" />
        <activity android:name=".Year3" />
        <activity android:name=".CHEMICAL2" />
        <activity android:name=".CIVIL2" />
        <activity android:name=".MECH2" />
        <activity android:name=".PHARMA2" />
        <activity android:name=".IT2" />
        <activity android:name=".EEE2" />
        <activity android:name=".ECE2" />
        <activity android:name=".CSE2" />
        <activity android:name=".CHEMICAL" />
        <activity android:name=".CIVIL" />
        <activity android:name=".MECH" />
        <activity android:name=".PHARMA" />
        <activity android:name=".IT" />
        <activity android:name=".EEE" />
        <activity android:name=".ECE" />
        <activity android:name=".CSE" />
        <activity android:name=".Year4" />
        <activity android:name=".Year2" />
        <activity android:name=".Year1" />
        <activity android:name=".ExamPrep" />
        <activity android:name=".About" />
        <activity android:name=".Notices" />
        <activity android:name=".Events" />
        <activity android:name=".Calendar" />
        <activity android:name=".Attendance" />
        <activity android:name=".Launch" />
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>