java.lang.String中android.os.Bundle.getString（java.lang.String中）

Question

我MainActivity.class經由setOnClickListener調用putExtra朝向SecondActivity.class

Intent intent = new Intent(MainActivity.this, SecondActivity.class); 
intent.putExtra("sentString", stringName); 
startActivity(intent); 

SecondActivity.class setOnClickListener

// Recieve the extra sent from MainActivity.class 
Intent SecondActivityIntent = getIntent(); 
String mString = SecondActivityIntent .getExtras().getString("sentString"); 

// Send extra to another activity ThirdActivity.class 
SecondActivityIntent.putExtra("sentString", mString); 
startActivity(SecondActivityIntent); 

ThirdActivity.class setOnClickListener

// Recieve extra from SecondActivity.class 
Intent thirdActivityintent = getIntent(); 
String mString = thirdActivityintent.getExtra().getString("sentString"); 
// This time I am calling SecondActivity.class but I will not send extra 
thirdActivityintent = new Intent(ThirdActivity.this, SecondActivity.class); 
startActivity(thirdActivityintent); 

ThirdActivity.class導致一個

'java.lang.String中android.os.Bundle.getString（java.lang.String中）' 對空對象引用

這個錯誤是什麼意思？是否因爲SecondActivity.class期望從任何調用活動中獲得額外的功能？我不打算將ExtraExtra放在ThirdActivity上，或者我會強迫。這怎麼解決？

Answer 1

是因爲SecondActivity.class期望從任何調用活動中獲取額外的內容嗎？

是的。

這怎麼解決？

將一個默認值和一個空檢查

// Receive the extra sent from MainActivity.class 
Bundle extras = getIntent().getExtras(); 
String mString = "default"; 

if (extras != null) { 
    mString = extras.getString("sentString"); 
} 

Answer 2

變化

.getExtras().getString("sentString"); 

到

.getExtras().getString("sentString", "defaultValue"); 

Answer 3

把它變成像這樣 FirstActivity

Intent intent = new Intent(MainActivity.this, SecondActivity.class); 
intent.putExtra("sentString", stringName); 
startActivity(intent); 

在SecondActivity

// Recieve the extra sent from MainActivity.class 
Intent SecondActivityIntent = getIntent(); 
String mString = SecondActivityIntent .getStringExtra("sentString"); 
// Send extra to another activity ThirdActivity.class 
Intent thirdIntent = new Intent(SecondActivity.this, ThirdActivity.class); 
thirdIntent.putExtra("sentString", mString); 
startActivity(thirdIntent); 

的ThirdActivity

// Recieve extra from SecondActivity.class 
Intent thirdActivityintent = getIntent(); 
String mString = thirdActivityintent.getStringExtra("sentString"); 
// Just finish Activity 
finish();