为什么我收到错误？：参数 t 具有不兼容的上限：首选项和首选项

Question

我无法解决错误的问题：

incompatible types: no unique maximal instance exists for type variable T with upper bounds com.velocat.cmap.Preference,androidx.preference.Preference

        Preference preference = findPreference("button");

                                              ^

  where T is a type-variable:

    T extends androidx.preference.Preference declared in method <T>findPreference(CharSequence)

SettingsFragment.java

import android.os.Bundle;

import android.preference.Preference;

import android.view.LayoutInflater;

import android.view.View;

import android.view.ViewGroup;

import androidx.preference.PreferenceFragmentCompat;

public class SettingsFragmentActivity extends PreferenceFragmentCompat {

    Preference preference;

    @Override

    public void onCreatePreferences(Bundle savedInstanceState, String rootKey) {

        addPreferencesFromResource(R.xml.setting);

        Preference preference = findPreference("preference1");

    }

    @Override

    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {

        View view = super.onCreateView(inflater, container, savedInstanceState);

        return view;

    }

}

buld.gradle的一部分

dependencies {

    implementation fileTree(dir: 'libs', include: ['*.jar'])

    implementation 'androidx.appcompat:appcompat:1.1.0'

    implementation 'androidx.legacy:legacy-support-v4:1.0.0'

    implementation 'com.google.android.material:material:1.0.0'

    implementation 'androidx.constraintlayout:constraintlayout:1.1.3'

    implementation 'androidx.navigation:navigation-fragment:2.1.0'

    implementation 'androidx.navigation:navigation-ui:2.1.0'

    implementation 'com.google.android.gms:play-services-location:17.0.0'

    testImplementation 'junit:junit:4.12'

    androidTestImplementation 'androidx.test.ext:junit:1.1.1'

    androidTestImplementation 'androidx.test.espresso:espresso-core:3.2.0'

    implementation 'androidx.preference:preference:1.1.0'

}

我重新阅读了搜索中所有可能的内容，但没有找到问题的解决方案。有谁知道如何消除这个错误？

如果您对这个主题有任何澄清，我将不胜感激。

Answer 1

我猜你输入了错误的Preference&nbsp;应该是import&nbsp;androidx.preference.Preference当您扩展androidx.preference.PreferenceFragmentCompat&nbsp;并根据文档返回时androidx.preference.Preference

Answer 2

只需导入这些库即可导入 androidx.preference.Preference；导入 androidx.preference.PreferenceFragmentCompat;