Question

我一直得到null而不是预期的字符串。我已经通过getSharedPreferences应用程序的上下文和正确的密钥。我将上传XML文件。我不知道这是怎么回事。

import React, {Component} from "react"; class RGBGuesser extends Component { constructor(){ super(); this.state = { correctCount: 0, displayCorrect: 0, colors: "", chosenResult: "", chosenCorrect: 0, } } componentDidMount = () => { this.startGame(); } initialGameState = () => { this.setState({ colors: this.displayRandom(6) }) } restart = () => { this.initialGameState(); this.setState({ chosenResult: "", chosenCorrect: 0, displayCorrect: 0 }) } pickSquare = () => { let colorRan = Math.floor(Math.random() * this.state.colors.length); return this.state.colors[colorRan] } displayRandom = amountSquares => { const colorArr = []; for(let i = 0; i < amountSquares; i++){ colorArr.push(this.chooseRandom()); } return colorArr; } chooseRandom = () => { let rColor = Math.floor(Math.random() * 256); let gColor = Math.floor(Math.random() * 256); let bColor = Math.floor(Math.random() * 256); return `rgb(${rColor}, ${gColor}, ${bColor})`; } chooseSquare = () => { //where i would want to do the logic of clicking the square and comparing it with the rgb color displayed on screen } startGame = () => { this.initialGameState(); this.restart(); } render(){ let correctColor = this.pickSquare(); return( <div> <h1 id="header">RGB Color Guesser</h1> <h3 id="mainColor">{correctColor}</h3> <h3 id="result"></h3> <h3 id="showCorrect">Number Correct: <span id="correctCount">0</span></h3> <button id="startOver" onClick={this.restart}>Start Over</button> <div id="colorGrid"> <div className="coloredSquare" onClick={this.chooseSquare} style={{backgroundColor: this.state.colors[0]}}></div> <div className="coloredSquare" onClick={this.chooseSquare} style={{backgroundColor: this.state.colors[1]}}></div> <div className="coloredSquare" onClick={this.chooseSquare} style={{backgroundColor: this.state.colors[2]}}></div> <div className="coloredSquare" onClick={this.chooseSquare} style={{backgroundColor: this.state.colors[3]}}></div> <div className="coloredSquare" onClick={this.chooseSquare} style={{backgroundColor: this.state.colors[4]}}></div> <div className="coloredSquare" onClick={this.chooseSquare} style={{backgroundColor: this.state.colors[5]}}></div> </div> </div> ) } } export default RGBGuesser;在线 java.lang.NullPointerException: println needs a message 首选项文件中没有显示任何内容，但是键是正确的，momentData是有效的SharedPreferences对象。至少根据调试器。

这是XML，下面是代码。

Log.d("MomentPrefTimeStamp", momentData.getString("caption", null));

为什么我不能使用正确的密钥和上下文来获取数据？

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<?xml version='1.0' encoding='utf-8' standalone='yes' ?>
<map>
<string name="time_stamp">1529509324</string>
<string name="img_uri">content://com.example.android.fileprovider/my_images/JPEG_20180620_114201_1480896410651074556.jpg</string>
<string name="caption">Captionas</string>
</map>

Answer 1

如果要通过字符串技巧和文件目录获取SharedPreferences，请确保从文件名中删除扩展名。我不知道为什么它仍然给我一个SharedPreference对象而不是一个空指针异常，但这就是问题所在。

1234242_JPEG.xml必须为1234242_JPEG才能获取正确的SharedPreference文件。下面是修复程序。

                    String name = title.substring(0, title.lastIndexOf('.'));
                    Log.d("MomentName", name);
                    SharedPreferences momentData = this.getSharedPreferences(name, this.MODE_PRIVATE);

SharedPreferences getString返回null

1 个答案: