我正在尝试编写一个简单的Android应用程序来熟悉sdk，我无法弄清楚为什么setText方法没有改变TextView。基本上我想要发生的是用户输入一个字符串，让用户选择在字符串上运行哪个方法并将输出设置为Textview但我似乎无法设置TextView。我试过在onCreate中调用方法，在case之后的switch中，在每种情况下都没有将文本设置为输出值。有谁知道我做错了什么？
package com.example.firstapp;
import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
public class TextChange extends Activity implements OnClickListener{
Button findUpperCase, everyOther, vowelReplace, vowelCount;
EditText input;
TextView output;
String inputText, outputText;
@Override
protected void onCreate(Bundle savedInstanceState) {
// TODO Auto-generated method stub
super.onCreate(savedInstanceState);
setContentView(R.layout.textchanger);
initializeVar();
output.setText(outputText);
}
public void initializeVar(){
findUpperCase = (Button) findViewById(R.id.finduppercase);
everyOther = (Button) findViewById(R.id.everyother);
vowelReplace = (Button) findViewById(R.id.vreplace);
vowelCount = (Button) findViewById(R.id.vcount);
input = (EditText) findViewById(R.id.stringinput);
output = (TextView) findViewById(R.id.output);
}
public static String findUpperCase(String x){
//Initialize output value
String output = "";
//For loop to loop through each character of the string
for (int i = 0; i <= x.length()-1; i++)
{
//Convert letter to char value and compare it to the ASCII values for capital letters
if (Character.isUpperCase(x.charAt(i)))
{
//Add each capital letter to the output string
output += x.substring(i, i+1) + " ";
}
}
//If not uppercase letters tell user
if (output.equals("")){
output = "No upper case characters";
}
//Return the capital letters or message to user and exit method
return output;
}
//Method used to get every other letter
public static String everyOther(String x){
//Set initial value of output
String output = "";
//Use for loop to get every other character by incrementing i by 2 each time
for(int i=0; i<=x.length() - 1; i+=2){
//Set letter equal to a temperary holder
char temp = x.charAt(i);
//If it is the first letter add to output without a space preceeding it
if (i == 0){
//New output is set as the old output plus the temp value without a space
output = output + temp;
}
//If it is not the first letter do this
else{
//New output is set as the old output plus the temp value with a space
output = output + " " + temp;
}
}
//Return the output
return output;
}
//Method to replace the vowel with "_"
public static String vowelReplace(String x){
//Search each string for vowels and ignore the case, when found replace with a "_"
String output = x.replaceAll("(?i)[aeiou]","_");
//Return the output
return output;
}
//Method to count the vowels
public static int vowelCount(String x){
//Set a counter
int count = 0;
//Set an array of char characters containing all the letters
char vowels[] = {'a','e','i','o','u','A','E','I','O','U'};
//For loop to check each letter for vowels
for (int i = 0; i <= x.length() - 1; i++){
//For loop to check each character against values in vowels array
for(int z = 0; z <= 9; z++){
//If a vowel is found increment the count
if (x.charAt(i) == vowels[z]){
//Increment the count
count++;
}
}
}
//Return the number of vowels
return count;
}
//Method to identify the vowel positions
public static String vowelPositions(String x){
//Initialize an output variable
String output = "";
//Set a temp string variable
String values = "";
//Set an array of char characters containing all the letters
char vowels[] = {'a','e','i','o','u','A','E','I','O','U'};
//For loop to check each letter for vowels
for(int z = 0; z < x.length(); z++){
//For loop to check each character against values in vowels array
for (int i = 0; i <= 9; i++){
//Check if each character is equal to any value in the array value
if (x.charAt(z) == vowels[i]){
//If it is the first vowel found do not add a space before adding to output
if(output.equals("")){
//Set first value of output
output = "[" + z + "]";
}
else{
//Add each position of the vowels to the output string
values = " [" + z + "]";
//Set new value of outputs to old value plus the value of values
output = output + values;
}
}
}
}
//Return the location of the vowels
return "Vowels are located at the following indexes:" + output;
}
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
inputText = input.getText().toString();
switch(v.getId()){
case R.id.finduppercase:
outputText = findUpperCase(inputText);
break;
case R.id.everyother:
outputText = everyOther(inputText);
break;
case R.id.vcount:
outputText=Integer.toString(vowelCount(inputText));
break;
case R.id.vpos:
outputText = vowelPositions(inputText);
break;
case R.id.vreplace:
outputText = vowelReplace(inputText);
break;
}
}
}
答案 0 :(得分：1)
有谁知道我做错了什么？
在onCreate()，您在setText()上呼叫TextView，但您传递的参数为null，因为您尚未初始化output。
您的代码中没有其他地方您正在调用setText()。
答案 1 :(得分：1)
首先，你在setText方法中没有调用Onclick，其次你没有将监听器设置为按钮
1）将onClickListners设置为按钮
public void initializeVar(){
findUpperCase = (Button) findViewById(R.id.finduppercase);
everyOther = (Button) findViewById(R.id.everyother);
vowelReplace = (Button) findViewById(R.id.vreplace);
vowelCount = (Button) findViewById(R.id.vcount);
findUpperCase.setOnClickListener(this);
everyOther.setOnClickListener(this);
vowelReplace.setOnClickListener(this);
vowelCount.setOnClickListener(this);
}
2）onClick方法中的setText：
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
inputText = input.getText().toString();
switch(v.getId()){
case R.id.finduppercase:
outputText = findUpperCase(inputText);
output.setText(outputText);
break;
case R.id.everyother:
outputText = everyOther(inputText);
output.setText(outputText);
break;
case R.id.vcount:
outputText=Integer.toString(vowelCount(inputText));
output.setText(outputText);
break;
case R.id.vpos:
outputText = vowelPositions(inputText);
output.setText(outputText);
break;
case R.id.vreplace:
outputText = vowelReplace(inputText);
output.setText(outputText);
break;
}
}