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问不能将androidx.appcompat.widget.AppCompatTextView转换为android.widget.CheckedTextView
EN

Stack Overflow用户

提问于 2020-04-06 21:07:00

回答 1查看 953关注 0票数 0

我是Java中的android应用程序的新手。示例应用程序应该让我选择我想要在ListView中使用的货币。每次我想从列表中选择一种货币时，应用程序崩溃，我得到错误：

E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.a5_listview, PID: 12333
    java.lang.ClassCastException: androidx.appcompat.widget.AppCompatTextView cannot be cast to android.widget.CheckedTextView
        at com.example.a5_listview.MainActivity$1.onItemClick(MainActivity.java:48)

MainActivity.java

package com.example.a5_listview;

import androidx.appcompat.app.AppCompatActivity;

import android.app.ProgressDialog;
import android.content.Context;
import android.content.SharedPreferences;
import android.os.AsyncTask;
import android.os.Bundle;
import android.preference.PreferenceManager;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.CheckedTextView;
import android.widget.ListView;
import android.widget.Toast;

import com.google.gson.Gson;

import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.HashSet;
import java.util.List;
import java.util.Set;

public class MainActivity extends AppCompatActivity {

    List<nbpCurrency> currencies = new ArrayList<>();
    ListView listView;
    Context context;
    ProgressDialog progressDialog;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        listView = findViewById(R.id.listView);
        context = this;

        listView.setChoiceMode(ListView.CHOICE_MODE_MULTIPLE);
        listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
                CheckedTextView v = (CheckedTextView) view;
                boolean isCurrentChoice = v.isChecked();
                nbpCurrency currency = (nbpCurrency) listView.getItemAtPosition(position);
                currency.setChosen(isCurrentChoice);
            }
        });
        
        getCurrencies();
    }

    private void getCurrencies() {
        progressDialog = ProgressDialog.show(context, "Getting currencies",
                "Please wait...", true);

        AsyncTask.execute(new Runnable() {
            @Override
            public void run() {
                try {
                    URL nbpEndpoint =
                            new URL("http://api.nbp.pl/api/exchangerates/tables/a/");
                    HttpURLConnection nbpConnection =
                            (HttpURLConnection) nbpEndpoint.openConnection();
                    nbpConnection.setRequestProperty("Accept", "application/json");

                    if(nbpConnection.getResponseCode() == 200) {
                        InputStreamReader is =
                                new InputStreamReader(nbpConnection.getInputStream());
                        Gson gson = new Gson();
                        final nbpCurrencies[] nbpCurrenciesArray = gson.fromJson(is, nbpCurrencies[].class);
                        nbpConnection.disconnect();

                        runOnUiThread(new Runnable() {
                            @Override
                            public void run() {
                                currencies.addAll(Arrays.asList(nbpCurrenciesArray[0].getCurrencies()));
                                Collections.sort(currencies);
                                ArrayAdapter<nbpCurrency> arrayAdapter =
                                        new ArrayAdapter<nbpCurrency>(context,
                                                android.R.layout.simple_list_item_1, currencies);
                                listView.setAdapter(arrayAdapter);
                                selectChosen();
                                progressDialog.dismiss();
                            }
                        });
                    } else {
                        runOnUiThread(new Runnable() {
                            @Override
                            public void run() {
                                progressDialog.dismiss();
                                Toast.makeText(context, "There was a problem getting the data",
                                        Toast.LENGTH_LONG).show();
                            }
                        });
                    }
                } catch(Exception e) {
                    e.printStackTrace();

                    runOnUiThread(new Runnable() {
                        @Override
                        public void run() {
                            progressDialog.dismiss();
                            Toast.makeText(context, "There was a problem getting the data",
                                    Toast.LENGTH_LONG).show();
                        }
                    });
                }
            }
        });
    }

    private void selectChosen() {
        SharedPreferences pref =
                PreferenceManager.getDefaultSharedPreferences(getApplicationContext());
        Set<String> chosenCurrenciesCodes = pref.getStringSet("currenciesCodes", new HashSet<String>());

        for(int i = 0; i < currencies.size(); i++) {
            nbpCurrency currency = currencies.get(i);
            if(chosenCurrenciesCodes.contains(currency.getCode())) {
                currency.setChosen(true);
                listView.setItemChecked(i, true);
            }
        }
    }

    public void saveChosen(View view) {
        SharedPreferences pref =
                PreferenceManager.getDefaultSharedPreferences(getApplicationContext());
        Set<String> chosenCurrenciesCodes = new HashSet<>();

        for(nbpCurrency currency : currencies) {
            if(currency.isChosen()) {
                chosenCurrenciesCodes.add(currency.getCode());
            }
        }

        pref.edit().putStringSet("currenciesCodes", chosenCurrenciesCodes).apply();
    }
}

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout 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=".MainActivity">

    <ListView
        android:id="@+id/listView"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_marginStart="16dp"
        android:layout_marginTop="8dp"
        android:layout_marginEnd="16dp"
        android:layout_marginBottom="8dp"
        app:layout_constraintBottom_toTopOf="@+id/button"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent">
    </ListView>

    <Button
        android:id="@+id/button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginBottom="16dp"
        android:onClick="saveChosen"
        android:text="Save"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent" />

</androidx.constraintlayout.widget.ConstraintLayout>

nbpCurrencies.java

package com.example.a5_listview;

import com.google.gson.annotations.SerializedName;

public class nbpCurrencies {
    private String table;
    private String no;
    private String effectiveDate;

    @SerializedName(value = "rates")
    private nbpCurrency[] currencies;

    public String getTable() {
        return table;
    }

    public void setTable(String table) {
        this.table = table;
    }

    public String getNo() {
        return no;
    }

    public void setNo(String no) {
        this.no = no;
    }

    public String getEffectiveDate() {
        return effectiveDate;
    }

    public void setEffectiveDate(String effectiveDate) {
        this.effectiveDate = effectiveDate;
    }

    public nbpCurrency[] getCurrencies() {
        return currencies;
    }

    public void setCurrencies(nbpCurrency[] currencies) {
        this.currencies = currencies;
    }
}

nbpCurrency.java

package com.example.a5_listview;

class nbpCurrency implements Comparable<nbpCurrency> {
    private String currency;
    private String code;
    private double mid;

    private transient boolean chosen = false;

    public nbpCurrency() {
    }

    public String getCurrency() {
        return currency;
    }

    public void setCurrency(String currency) {
        this.currency = currency;
    }

    public String getCode() {
        return code;
    }

    public void setCode(String code) {
        this.code = code;
    }

    public double getMid() {
        return mid;
    }

    public void setMid(double mid) {
        this.mid = mid;
    }

    public boolean isChosen() {
        return chosen;
    }

    public void setChosen(boolean chosen) {
        this.chosen = chosen;
    }

    @Override
    public String toString() {
        return String.format("%s [%s: %.3f]", code, currency, mid);
    }

    @Override
    public int compareTo(nbpCurrency nbpCurrency) {
        return code.compareTo(nbpCurrency.getCode());
    }
}

在日志中，我可以看到导致所有混乱的代码行：CheckedTextView v = (CheckedTextView) view;

该错误的原因是什么？我已经在StackOverflow上查看了其他答案，但我仍然找不到任何解决方案。也许我只是看不到一个明显的错误。谢谢你的帮助。

java

android

android-studio

回答 1

Stack Overflow用户

回答已采纳

发布于 2020-04-06 21:23:11

listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
                CheckedTextView v = (CheckedTextView) view;
                boolean isCurrentChoice = v.isChecked();
                nbpCurrency currency = (nbpCurrency) listView.getItemAtPosition(position);
                currency.setChosen(isCurrentChoice);
            }
        });

您可以在这里设置一个ClickListener。适配器返回的view字段为TextView。这就是你获得CastException的方式。在这个方法中，您还可以获得id和position字段，并且可以使用它们。

如果您希望启用多项选择，则需要使用如下所示的另一个布局构建ArrayAdapter：

ArrayAdapter<nbpCurrency> arrayAdapter =
    new ArrayAdapter<nbpCurrency>(context,
        android.R.layout.simple_list_item_multiple_choice, currencies);