Question

我正在构建一个简单的应用程序，我想从手机中检索所有联系人并将其显示在textView中。使用加载器CallBack方法，但按下加载按钮后我得到一个空白屏幕。还提供了相同的读写权限。在下面发布我的代码，请帮忙。提前致谢

MainActivity.java

package com.example.sumeet.contentproviderdemoyoutube;

import android.app.LoaderManager;
import android.content.CursorLoader;
import android.content.Loader;
import android.database.Cursor;
import android.os.Bundle;
import android.provider.ContactsContract;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity implements View.OnClickListener, LoaderManager.LoaderCallbacks<Cursor> {
    TextView textView;
    Button button;
    String TAG = "Show";

    private String mColumnProjection[] = new String[]{
            ContactsContract.Contacts.DISPLAY_NAME_PRIMARY,
            ContactsContract.Contacts.CONTACT_STATUS,
            ContactsContract.Contacts.HAS_PHONE_NUMBER};

    private String mSelectionClause = ContactsContract.Contacts.DISPLAY_NAME_PRIMARY + "='Simpi'";
    private String[] mSelectionArguments = new String[]{"Simpi"};
    private String mOrderBy = ContactsContract.Contacts.DISPLAY_NAME_PRIMARY;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        textView = (TextView) findViewById(R.id.tv_show);
        button = (Button) findViewById(R.id.load);
        //   ContentResolver contentResolver = getContentResolver();
//        Cursor cursor = contentResolver.query(ContactsContract.Contacts.CONTENT_URI,
//                mColumnProjection,
//                mSelectionClause,
//                null,
//                null);


    }

    public void onClick(View view) {
        switch (view.getId()) {
            case R.id.load:
                getLoaderManager().initLoader(1, null, this);
                Toast.makeText(this, "Button Clicked", Toast.LENGTH_SHORT).show();
                break;
            default:
                break;
        }

    }


    @Override
    public Loader<Cursor> onCreateLoader(int i, Bundle bundle) {
        if (i == 1) {
            Toast.makeText(this, "Inside onloader", Toast.LENGTH_SHORT).show();
            return new CursorLoader(this, ContactsContract.Contacts.CONTENT_URI, null, null, null, null);
        }

        return null;
    }

    @Override
    public void onLoadFinished(Loader<Cursor> loader, Cursor cursor) {
        Toast.makeText(this, "OnFinish", Toast.LENGTH_SHORT).show();
        if (cursor != null && cursor.getCount() > 0) {
            StringBuilder stringBuilder = new StringBuilder("");
            while (cursor.moveToNext()) {
                stringBuilder.append(cursor.getString(0) + "," + cursor.getString(1) + "," + cursor.getString(2) + "\n");
            }
            textView.setText(stringBuilder.toString());
        } else {
            textView.setText("No Contacts to display");
        }

    }

    @Override
    public void onLoaderReset(Loader<Cursor> loader) {
        Toast.makeText(this, "onLoader", Toast.LENGTH_SHORT).show();
    }
}

activity_main.xml中

<?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"
    android:orientation="vertical"
    tools:context="com.example.sumeet.contentproviderdemoyoutube.MainActivity">

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

    <TextView
        android:id="@+id/tv_show"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Hello World!"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

</LinearLayout>

的AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.sumeet.contentproviderdemoyoutube">

    <uses-permission android:name="android.permission.READ_CONTACTS"></uses-permission>
    <uses-permission android:name="android.permission.WRITE_CONTACTS"></uses-permission>

    <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">
        <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>

Answer 1

将onClick()中的init loader调用更改为

getLoaderManager().initLoader(1, null, this).forceLoad();

同样documentation说明

Blockquote必须使用CursorLoader(Context, Uri, String[], String, String[], String)或使用CursorLoader(Context)创建一个空实例并使用setUri(Uri)填充所需的参数，使用要执行的查询的完整信息构建CursorLoader。，setSelection(String)，setSelectionArgs(String[])，setSortOrder(String)和setProjection(String[])。

尝试将此信息提供给CursorLoader构造函数

无法使用Loader回调联系人回调方法

1 个答案: