《Android编程权威指南》第二版 第二章 挑战练习

2.9 挑战练习：添加后退按钮

1.首先在布局文件里新建一个线性布局，在线性布局里新建一个priv_button,再将之前的next_button添加进去

2.在QuizActivity.java中添加逻辑方法

package com.example.fkxx.geoquiz;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
import android.widget.Toast;

public class QuizActivity extends AppCompatActivity {

    private Button mTrueButton;
    private Button mFalseButton;
    private Button mNextButton;
    private Button mPrivButton;
    private TextView mQuestionTextView;

    private Question[] mQuestionBank = new Question[]{
            new Question(R.string.question_oceans,true),
            new Question(R.string.question_mideast,false),
            new Question(R.string.question_asia,false),
            new Question(R.string.question_americas,true),
            new Question(R.string.question_africa,true),
    };

    private void updateQuestion(){
        int question = mQuestionBank[mCurrentIndex].getTextResId();
        mQuestionTextView.setText(question);
    }

    private void checkAnswer(boolean userPressedTrue){
        boolean answerIsTrue = mQuestionBank[mCurrentIndex].isAnswerTrue();
        int messageResId = 0;
        if (userPressedTrue == answerIsTrue){
            messageResId = R.string.correct_toast;
        }else {
            messageResId = R.string.incorrect_toast;
        }
        Toast.makeText(this,messageResId,Toast.LENGTH_SHORT).show();
    }

    private int mCurrentIndex = 0;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_quiz);

        mTrueButton = (Button)findViewById(R.id.true_button);
        mFalseButton = (Button)findViewById(R.id.false_button);
        mNextButton = (Button)findViewById(R.id.next_button);
        mPrivButton = (Button)findViewById(R.id.priv_button);
        mQuestionTextView = (TextView)findViewById(R.id.question_text_view);

        mTrueButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
//                Toast.makeText(QuizActivity.this,R.string.correct_toast,Toast.LENGTH_SHORT).show();
                checkAnswer(true);
            }
        });
        mFalseButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
//            Toast.makeText(QuizActivity.this,R.string.incorrect_toast,Toast.LENGTH_SHORT).show();
                checkAnswer(false);
            }
        });
        mNextButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {

                mCurrentIndex = (mCurrentIndex + 1)%mQuestionBank.length;
//                int question = mQuestionBank[mCurrentIndex].getTextResId();
//                mQuestionTextView.setText(question);
                updateQuestion();
            }
        });
        mPrivButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                if (mCurrentIndex<1){
                    mCurrentIndex+=mQuestionBank.length;
                }
                mCurrentIndex = (mCurrentIndex - 1)%mQuestionBank.length;
                updateQuestion();
            }
        });
        updateQuestion();
    }
}

监听器部分的代码如下：

mPrivButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                if (mCurrentIndex<1){
                    mCurrentIndex+=mQuestionBank.length;
                }
                mCurrentIndex = (mCurrentIndex - 1)%mQuestionBank.length;
                updateQuestion();
            }
        });

如果不加入该if判断,当在首个问题时点击PRIV按钮会报错.

2.10 挑战练习：从按钮到图标按钮

将布局文件修改成如下

之后报了如下错误，但是不影响程序运行

java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.fkxx.geoquiz/com.example.fkxx.geoquiz.QuizActivity}: java.lang.ClassCastException: android.support.v7.widget.AppCompatImageButton cannot be cast to android.widget.Button

于是build-cleanproject了一下，解决问题

看书上有添加android:contentDescription属性

遂将布局文件修改如下：