Android学习笔记（一）：AndroidStudio无法从静态上下文中引入非静态方法setGravity()和show()无法从静态上下文中引入非静态方法

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我是靠谱客的博主土豪鸡，最近开发中收集的这篇文章主要介绍Android学习笔记（一）：AndroidStudio无法从静态上下文中引入非静态方法setGravity()和show()无法从静态上下文中引入非静态方法，觉得挺不错的，现在分享给大家，希望可以做个参考。

概述

无法从静态上下文中引入非静态方法

笔者在学习《Android编程权威指南第三版》的过程中，在第一章挑战练习“定制toast消息”遇到了问题，笔者由于缺乏java基础，迟迟不能解决。

原代码

package com.bignerdranch.android.geoquiz;

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

public class QuizActivity extends AppCompatActivity {

    private Button mTrueButton;
    private Button mFalseButton;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_quiz);

        mTrueButton = (Button) findViewById(R.id.true_button);
        mTrueButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Toast.makeText(QuizActivity.this,
                        R.string.correct_toast,
                        Toast.LENGTH_SHORT).show();
            }
        });

        mFalseButton = (Button) findViewById(R.id.false_button);
        mFalseButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Toast.makeText(QuizActivity.this,
                        R.string.incorrect_toast,
                        Toast.LENGTH_SHORT).show();
            }
        });
    }
}

这是第一章已经给出的关于toast部分的代码，现在要求更改代码使toast消息从屏幕顶部弹出而不是底部弹出，这需要用到setGravity.TOP命令。我尝试写出了如下代码：

报错的代码

package com.bignerdranch.android.geoquiz;

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


public class QuizActivity extends AppCompatActivity {

    private Button mTrueButton;
    private Button mFalseButton;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_quiz);

        mTrueButton = findViewById(R.id.true_button);
        mTrueButton.setOnClickListener(new View.OnClickListener(){
            @Override
            public void onClick(View v){
                Toast.makeText(QuizActivity.this,
                        R.string.correct_toast,
                        Toast.LENGTH_SHORT);
                Toast.setGravity(Gravity.TOP,0,0);//该句报错
                Toast.show();//该句报错

            }
        });

        mFalseButton = findViewById(R.id.false_button);
        mFalseButton.setOnClickListener(new View.OnClickListener(){
            @Override
            public void onClick(View v){
                Toast.makeText(QuizActivity.this,
                        R.string.incorrect_toast,
                        Toast.LENGTH_SHORT);
                Toast.setGravity(Gravity.TOP,0,0);//该句报错
                Toast.show();//该句报错

            }
        });
    }
}

编译问题截图

问题分析

在AppCompaActivity下onCreate的静态类环境中错误的引用了非静态方法。正确的做法，应该通过Toast toast =Toast.***的方法来实现。

解决问题后的代码

public class QuizActivity extends AppCompatActivity {

    private Button mTrueButton;
    private Button mFalseButton;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_quiz);

        mTrueButton = findViewById(R.id.true_button);
        mTrueButton.setOnClickListener(new View.OnClickListener(){
            @Override
            public void onClick(View v){
                Toast toast1 =Toast.makeText(QuizActivity.this,
                        R.string.correct_toast,
                        Toast.LENGTH_SHORT);
                toast1.setGravity(Gravity.TOP,0,0);
                toast1.show();


            }
        });

        mFalseButton = findViewById(R.id.false_button);
        mFalseButton.setOnClickListener(new View.OnClickListener(){
            @Override
            public void onClick(View v){
                Toast toast2 =Toast.makeText(QuizActivity.this,
                        R.string.incorrect_toast,
                        Toast.LENGTH_SHORT);
                toast2.setGravity(Gravity.TOP,0,0);
                toast2.show();

            }
        });
    }
}