做一个聊天框，添加了一个UITextField，打字的时候有不小的几率会crash，请求帮助
这是添加的代码
760
这是报错的提示
761
在线等大神指导。谢谢
详细的crash信息
0
CoreGraphics 0x31e09fcc CGFontStrikeRelease + 71
1
CoreGraphics 0x31e09f0b CGFontCacheUnlockStrike + 230
2
CoreGraphics 0x31e09a89 CGGlyphLockUnlock + 52
3
libRIP.A.dylib 0x34604acd ripc_DrawGlyphs + 1888
4
CoreGraphics 0x31e05361 CGContextDelegateDrawGlyphs + 44
5
CoreGraphics 0x31ee530d draw_glyphs + 396
6
CoreGraphics 0x31e05109 CGContextShowGlyphsWithAdvances + 380
7
WebCore 0x3664552b _ZN7WebCoreL22showGlyphsWithAdvancesERKNS_10FloatPointEPKNS_14SimpleFontDataEP9CGContextPKtPK6CGSizem + 1918
8
WebCore 0x36644c8f _ZNK7WebCore4Font10drawGlyphsEPNS_15GraphicsContextEPKNS_14SimpleFontDataERKNS_11GlyphBufferEiiRKNS_10FloatPointEb + 1078
9
WebCore 0x36644525 _ZNK7WebCore4Font14drawSimpleTextEPNS_15GraphicsContextERKNS_7TextRunERKNS_10FloatPointEii + 348
10
WebCore 0x366443a3 _ZNK7WebCore4Font8drawTextEPNS_15GraphicsContextERKNS_7TextRunERKNS_10FloatPointEii + 134
11
WebKit 0x34fd86ef _ZL11drawAtPointPKtiRKN7WebCore10FloatPointERKNS1_4FontEPNS1_15GraphicsContextEbPNS1_10BidiStatusEi + 210
12
WebKit 0x34fda56b - + 3690
13
WebKit 0x34f52187 - + 114